[PATCH v5 00/13] drm/trace: Mirror DRM debug logs to tracefs

[PATCH v5 00/13] drm/trace: Mirror DRM debug logs to tracefs

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

This series is the latest in my journey to create a lightweight,
always-on "flight recorder" (name credit Weston) of drm logs. This
incarnation uses a trace_array to keep logs in memory exposed through
tracefs. Users and distros can enable drm logs by using the drm.trace
module parameter to choose the debug categories they are interested in.

The set has ballooned a little bit since the last version. Reason being
is that I decided to return true from drm_debug_enabled if trace was
enabled. This should make it easier and more seamless for driver
developers to use the correct interface, but meant I needed to audit all
uses of drm_debug_enabled and drm_debug_printer.

Out of all those calls, there are 3 situations which arose:
1- The logs should only go to syslog:
	I've converted these to use the drm_debug_syslog variant of
	enable check/printer.

2- The logs should go to both syslog/trace, but were using pr_debug():
	I've converted these to use the proper drm logging helper. In
	cases which used a drm_printer I've had to use a new
	drm_debug_category_printer to ensure they are routed correctly.

3- The logs should go to both syslog/trace and are using drm logging fns:
   	These are untouched and should be routed to the appropriate
	place(s)


Sean Paul (13):
  drm/mipi_dbi: Convert pr_debug calls to DRM_DEBUG_DRIVER
  drm/sil164: Convert dev_printk to drm_dev_dbg
  drm/i915/utils: Replace dev_printk with drm helpers
  drm/msm/dpu: Replace definitions for dpu debug macros
  drm/print: rename drm_debug* to be more syslog-centric
  drm/amd: Gate i2c transaction logs on drm_debug_syslog
  drm/etnaviv: Change buffer dump checks to target syslog
  drm/nouveau: Change debug checks to specifically target syslog
  drm/i915: Change infoframe debug checks to specify syslog
  drm/print: Add drm_debug_category_printer
  drm/mst: Convert debug printers to debug category printers
  drm/i915: Use debug category printer for welcome message
  drm/print: Add tracefs support to the drm logging helpers

 Documentation/gpu/drm-uapi.rst               |   6 +
 drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c   |   4 +-
 drivers/gpu/drm/drm_dp_mst_topology.c        |   9 +-
 drivers/gpu/drm/drm_drv.c                    |   3 +
 drivers/gpu/drm/drm_mipi_dbi.c               |   8 +-
 drivers/gpu/drm/drm_print.c                  | 228 ++++++++++++++++---
 drivers/gpu/drm/etnaviv/etnaviv_buffer.c     |   8 +-
 drivers/gpu/drm/i2c/sil164_drv.c             |  12 +-
 drivers/gpu/drm/i915/display/intel_display.c |   4 +-
 drivers/gpu/drm/i915/i915_drv.c              |   3 +-
 drivers/gpu/drm/i915/i915_utils.c            |   5 +-
 drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h      |  20 +-
 drivers/gpu/drm/nouveau/dispnv50/disp.h      |   4 +-
 drivers/gpu/drm/nouveau/nouveau_drv.h        |   4 +-
 include/drm/drm_print.h                      |  96 +++++++-
 15 files changed, 318 insertions(+), 96 deletions(-)

-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 01/13] drm/mipi_dbi: Convert pr_debug calls to DRM_DEBUG_DRIVER

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

Use the drm logging helpers to output these messages to ensure they'll
be included by the drm tracefs instance.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/drm_mipi_dbi.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
index fd8d672972a9..ff6f83eeee09 100644
--- a/drivers/gpu/drm/drm_mipi_dbi.c
+++ b/drivers/gpu/drm/drm_mipi_dbi.c
@@ -769,9 +769,7 @@ static int mipi_dbi_spi1e_transfer(struct mipi_dbi *dbi, int dc,
 	int i, ret;
 	u8 *dst;
 
-	if (drm_debug_enabled(DRM_UT_DRIVER))
-		pr_debug("[drm:%s] dc=%d, max_chunk=%zu, transfers:\n",
-			 __func__, dc, max_chunk);
+	DRM_DEBUG_DRIVER("dc=%d, max_chunk=%zu, transfers:\n", dc, max_chunk);
 
 	tr.speed_hz = mipi_dbi_spi_cmd_max_speed(spi, len);
 	spi_message_init_with_transfers(&m, &tr, 1);
@@ -893,9 +891,7 @@ static int mipi_dbi_spi1_transfer(struct mipi_dbi *dbi, int dc,
 	max_chunk = dbi->tx_buf9_len;
 	dst16 = dbi->tx_buf9;
 
-	if (drm_debug_enabled(DRM_UT_DRIVER))
-		pr_debug("[drm:%s] dc=%d, max_chunk=%zu, transfers:\n",
-			 __func__, dc, max_chunk);
+	DRM_DEBUG_DRIVER("dc=%d, max_chunk=%zu, transfers:\n", dc, max_chunk);
 
 	max_chunk = min(max_chunk / 2, len);
 
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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Re: [PATCH v5 01/13] drm/mipi_dbi: Convert pr_debug calls to DRM_DEBUG_DRIVER

[Sam Ravnborg]

Hi Sean Paul.
On Mon, Jun 08, 2020 at 05:04:51PM -0400, Sean Paul wrote:
> From: Sean Paul <seanpaul@chromium.org>
> 
> Use the drm logging helpers to output these messages to ensure they'll
> be included by the drm tracefs instance.
> 
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> 
> Changes in v5:
> -Added to the set
> ---
>  drivers/gpu/drm/drm_mipi_dbi.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
> index fd8d672972a9..ff6f83eeee09 100644
> --- a/drivers/gpu/drm/drm_mipi_dbi.c
> +++ b/drivers/gpu/drm/drm_mipi_dbi.c
> @@ -769,9 +769,7 @@ static int mipi_dbi_spi1e_transfer(struct mipi_dbi *dbi, int dc,
>  	int i, ret;
>  	u8 *dst;
>  
> -	if (drm_debug_enabled(DRM_UT_DRIVER))
> -		pr_debug("[drm:%s] dc=%d, max_chunk=%zu, transfers:\n",
> -			 __func__, dc, max_chunk);
> +	DRM_DEBUG_DRIVER("dc=%d, max_chunk=%zu, transfers:\n", dc, max_chunk);
Today we have drm_dbg(...) as the preferred logging method.

	Sam

>  
>  	tr.speed_hz = mipi_dbi_spi_cmd_max_speed(spi, len);
>  	spi_message_init_with_transfers(&m, &tr, 1);
> @@ -893,9 +891,7 @@ static int mipi_dbi_spi1_transfer(struct mipi_dbi *dbi, int dc,
>  	max_chunk = dbi->tx_buf9_len;
>  	dst16 = dbi->tx_buf9;
>  
> -	if (drm_debug_enabled(DRM_UT_DRIVER))
> -		pr_debug("[drm:%s] dc=%d, max_chunk=%zu, transfers:\n",
> -			 __func__, dc, max_chunk);
> +	DRM_DEBUG_DRIVER("dc=%d, max_chunk=%zu, transfers:\n", dc, max_chunk);
>  
>  	max_chunk = min(max_chunk / 2, len);
>  
> -- 
> Sean Paul, Software Engineer, Google / Chromium OS
> 
> _______________________________________________
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> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
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[PATCH v5 02/13] drm/sil164: Convert dev_printk to drm_dev_dbg

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

Use the drm debug helper instead of dev_printk in order to leverage the
upcoming tracefs support

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/i2c/sil164_drv.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i2c/sil164_drv.c b/drivers/gpu/drm/i2c/sil164_drv.c
index 741886b54419..b315a789fca2 100644
--- a/drivers/gpu/drm/i2c/sil164_drv.c
+++ b/drivers/gpu/drm/i2c/sil164_drv.c
@@ -43,11 +43,6 @@ struct sil164_priv {
 #define to_sil164_priv(x) \
 	((struct sil164_priv *)to_encoder_slave(x)->slave_priv)
 
-#define sil164_dbg(client, format, ...) do {				\
-		if (drm_debug_enabled(DRM_UT_KMS))			\
-			dev_printk(KERN_DEBUG, &client->dev,		\
-				   "%s: " format, __func__, ## __VA_ARGS__); \
-	} while (0)
 #define sil164_info(client, format, ...)		\
 	dev_info(&client->dev, format, __VA_ARGS__)
 #define sil164_err(client, format, ...)			\
@@ -359,8 +354,8 @@ sil164_probe(struct i2c_client *client, const struct i2c_device_id *id)
 	int rev = sil164_read(client, SIL164_REVISION);
 
 	if (vendor != 0x1 || device != 0x6) {
-		sil164_dbg(client, "Unknown device %x:%x.%x\n",
-			   vendor, device, rev);
+		drm_dev_dbg(&client->dev, DRM_UT_KMS,
+			    "Unknown device %x:%x.%x\n", vendor, device, rev);
 		return -ENODEV;
 	}
 
@@ -389,7 +384,8 @@ sil164_detect_slave(struct i2c_client *client)
 	};
 
 	if (i2c_transfer(adap, &msg, 1) != 1) {
-		sil164_dbg(adap, "No dual-link slave found.");
+		drm_dev_dbg(&adap->dev, DRM_UT_KMS,
+			    "No dual-link slave found.");
 		return NULL;
 	}
 
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 03/13] drm/i915/utils: Replace dev_printk with drm helpers

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

Use drm logging helpers to add support for the upcoming tracefs
implementation.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/i915/i915_utils.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_utils.c b/drivers/gpu/drm/i915/i915_utils.c
index f42a9e9a0b4f..99499c0885cf 100644
--- a/drivers/gpu/drm/i915/i915_utils.c
+++ b/drivers/gpu/drm/i915/i915_utils.c
@@ -30,10 +30,9 @@ __i915_printk(struct drm_i915_private *dev_priv, const char *level,
 	vaf.va = &args;
 
 	if (is_error)
-		dev_printk(level, kdev, "%pV", &vaf);
+		drm_dev_printk(kdev, level, "%pV", &vaf);
 	else
-		dev_printk(level, kdev, "[" DRM_NAME ":%ps] %pV",
-			   __builtin_return_address(0), &vaf);
+		drm_err(&dev_priv->drm, "%pV", &vaf);
 
 	va_end(args);
 
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 04/13] drm/msm/dpu: Replace definitions for dpu debug macros

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

The debug messages shouldn't be logged as errors when debug categories
are enabled. Use the drm logging helpers to do the right thing

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h | 20 ++++----------------
 1 file changed, 4 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
index 4e32d040f1e6..89c444ec3bb8 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
@@ -29,27 +29,15 @@
  * DPU_DEBUG - macro for kms/plane/crtc/encoder/connector logs
  * @fmt: Pointer to format string
  */
-#define DPU_DEBUG(fmt, ...)                                                \
-	do {                                                               \
-		if (drm_debug_enabled(DRM_UT_KMS))                         \
-			DRM_DEBUG(fmt, ##__VA_ARGS__); \
-		else                                                       \
-			pr_debug(fmt, ##__VA_ARGS__);                      \
-	} while (0)
+#define DPU_DEBUG(fmt, ...) DRM_DEBUG_KMS(fmt, ##__VA_ARGS__)
 
 /**
  * DPU_DEBUG_DRIVER - macro for hardware driver logging
  * @fmt: Pointer to format string
  */
-#define DPU_DEBUG_DRIVER(fmt, ...)                                         \
-	do {                                                               \
-		if (drm_debug_enabled(DRM_UT_DRIVER))                      \
-			DRM_ERROR(fmt, ##__VA_ARGS__); \
-		else                                                       \
-			pr_debug(fmt, ##__VA_ARGS__);                      \
-	} while (0)
-
-#define DPU_ERROR(fmt, ...) pr_err("[dpu error]" fmt, ##__VA_ARGS__)
+#define DPU_DEBUG_DRIVER(fmt, ...) DRM_DEBUG_DRIVER(fmt, ##__VA_ARGS__)
+
+#define DPU_ERROR(fmt, ...) DRM_ERROR(fmt, ##__VA_ARGS__)
 
 /**
  * ktime_compare_safe - compare two ktime structures
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 05/13] drm/print: rename drm_debug* to be more syslog-centric

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

In preparation for tracefs support, rename drm_debug related functions
to reflect that it targets the syslog. This will allow us to selectively
target syslog and/or tracefs.

No functional changes here.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/drm_print.c | 12 ++++++------
 include/drm/drm_print.h     | 13 +++++++++----
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 111b932cf2a9..2ff7a6ecc632 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -37,11 +37,11 @@
 #include <drm/drm_print.h>
 
 /*
- * __drm_debug: Enable debug output.
+ * __drm_debug_syslog: Enable debug output to system logs
  * Bitmask of DRM_UT_x. See include/drm/drm_print.h for details.
  */
-unsigned int __drm_debug;
-EXPORT_SYMBOL(__drm_debug);
+unsigned int __drm_debug_syslog;
+EXPORT_SYMBOL(__drm_debug_syslog);
 
 MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n"
 "\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n"
@@ -52,7 +52,7 @@ MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug cat
 "\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
 "\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
 "\t\tBit 8 (0x100) will enable DP messages (displayport code)");
-module_param_named(debug, __drm_debug, int, 0600);
+module_param_named(debug, __drm_debug_syslog, int, 0600);
 
 void __drm_puts_coredump(struct drm_printer *p, const char *str)
 {
@@ -160,11 +160,11 @@ void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_info);
 
-void __drm_printfn_debug(struct drm_printer *p, struct va_format *vaf)
+void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf)
 {
 	pr_debug("%s %pV", p->prefix, vaf);
 }
-EXPORT_SYMBOL(__drm_printfn_debug);
+EXPORT_SYMBOL(__drm_printfn_debug_syslog);
 
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
 {
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index 1c9417430d08..ce7675bf0d2b 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -35,7 +35,7 @@
 #include <drm/drm.h>
 
 /* Do *not* use outside of drm_print.[ch]! */
-extern unsigned int __drm_debug;
+extern unsigned int __drm_debug_syslog;
 
 /**
  * DOC: print
@@ -85,7 +85,7 @@ void __drm_puts_coredump(struct drm_printer *p, const char *str);
 void __drm_printfn_seq_file(struct drm_printer *p, struct va_format *vaf);
 void __drm_puts_seq_file(struct drm_printer *p, const char *str);
 void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
-void __drm_printfn_debug(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
 
 __printf(2, 3)
@@ -227,7 +227,7 @@ static inline struct drm_printer drm_info_printer(struct device *dev)
 static inline struct drm_printer drm_debug_printer(const char *prefix)
 {
 	struct drm_printer p = {
-		.printfn = __drm_printfn_debug,
+		.printfn = __drm_printfn_debug_syslog,
 		.prefix = prefix
 	};
 	return p;
@@ -319,9 +319,14 @@ enum drm_debug_category {
 	DRM_UT_DRMRES		= 0x200,
 };
 
+static inline bool drm_debug_syslog_enabled(enum drm_debug_category category)
+{
+	return unlikely(__drm_debug_syslog & category);
+}
+
 static inline bool drm_debug_enabled(enum drm_debug_category category)
 {
-	return unlikely(__drm_debug & category);
+	return drm_debug_syslog_enabled(category);
 }
 
 /*
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 06/13] drm/amd: Gate i2c transaction logs on drm_debug_syslog

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

Since the logs protected by these checks specifically target syslog,
use the new drm_debug_syslog_enabled() call to avoid triggering
these prints when only trace is enabled.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c b/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c
index 9bffbab35041..9bc6baddd302 100644
--- a/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c
+++ b/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c
@@ -233,7 +233,7 @@ static uint32_t smu_v11_0_i2c_transmit(struct i2c_adapter *control,
 	DRM_DEBUG_DRIVER("I2C_Transmit(), address = %x, bytes = %d , data: ",
 		 (uint16_t)address, numbytes);
 
-	if (drm_debug_enabled(DRM_UT_DRIVER)) {
+	if (drm_debug_syslog_enabled(DRM_UT_DRIVER)) {
 		print_hex_dump(KERN_INFO, "data: ", DUMP_PREFIX_NONE,
 			       16, 1, data, numbytes, false);
 	}
@@ -387,7 +387,7 @@ static uint32_t smu_v11_0_i2c_receive(struct i2c_adapter *control,
 	DRM_DEBUG_DRIVER("I2C_Receive(), address = %x, bytes = %d, data :",
 		  (uint16_t)address, bytes_received);
 
-	if (drm_debug_enabled(DRM_UT_DRIVER)) {
+	if (drm_debug_syslog_enabled(DRM_UT_DRIVER)) {
 		print_hex_dump(KERN_INFO, "data: ", DUMP_PREFIX_NONE,
 			       16, 1, data, bytes_received, false);
 	}
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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Re: [PATCH v5 06/13] drm/amd: Gate i2c transaction logs on drm_debug_syslog

[Christian König]

Am 08.06.20 um 23:04 schrieb Sean Paul:
> From: Sean Paul <seanpaul@chromium.org>
>
> Since the logs protected by these checks specifically target syslog,
> use the new drm_debug_syslog_enabled() call to avoid triggering
> these prints when only trace is enabled.

Mhm, of hand that doesn't looks like something which belongs into the 
syslog in the first place. Maybe convert it into a trace point instead?

>
> Signed-off-by: Sean Paul <seanpaul@chromium.org>

Acked-by: Christian König <christian.koenig@amd.com> either way.

>
> Changes in v5:
> -Added to the set
> ---
>   drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c b/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c
> index 9bffbab35041..9bc6baddd302 100644
> --- a/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c
> +++ b/drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c
> @@ -233,7 +233,7 @@ static uint32_t smu_v11_0_i2c_transmit(struct i2c_adapter *control,
>   	DRM_DEBUG_DRIVER("I2C_Transmit(), address = %x, bytes = %d , data: ",
>   		 (uint16_t)address, numbytes);
>   
> -	if (drm_debug_enabled(DRM_UT_DRIVER)) {
> +	if (drm_debug_syslog_enabled(DRM_UT_DRIVER)) {
>   		print_hex_dump(KERN_INFO, "data: ", DUMP_PREFIX_NONE,
>   			       16, 1, data, numbytes, false);
>   	}
> @@ -387,7 +387,7 @@ static uint32_t smu_v11_0_i2c_receive(struct i2c_adapter *control,
>   	DRM_DEBUG_DRIVER("I2C_Receive(), address = %x, bytes = %d, data :",
>   		  (uint16_t)address, bytes_received);
>   
> -	if (drm_debug_enabled(DRM_UT_DRIVER)) {
> +	if (drm_debug_syslog_enabled(DRM_UT_DRIVER)) {
>   		print_hex_dump(KERN_INFO, "data: ", DUMP_PREFIX_NONE,
>   			       16, 1, data, bytes_received, false);
>   	}

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[PATCH v5 07/13] drm/etnaviv: Change buffer dump checks to target syslog

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

Since the logs protected by these checks specifically target syslog,
use the new drm_debug_syslog_enabled() call to avoid triggering
these prints when only trace is enabled.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/etnaviv/etnaviv_buffer.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_buffer.c b/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
index 76d38561c910..7713474800e8 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
@@ -353,7 +353,7 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
 
 	lockdep_assert_held(&gpu->lock);
 
-	if (drm_debug_enabled(DRM_UT_DRIVER))
+	if (drm_debug_syslog_enabled(DRM_UT_DRIVER))
 		etnaviv_buffer_dump(gpu, buffer, 0, 0x50);
 
 	link_target = etnaviv_cmdbuf_get_va(cmdbuf,
@@ -509,13 +509,13 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
 		 etnaviv_cmdbuf_get_va(buffer, &gpu->mmu_context->cmdbuf_mapping)
 		 + buffer->user_size - 4);
 
-	if (drm_debug_enabled(DRM_UT_DRIVER))
+	if (drm_debug_syslog_enabled(DRM_UT_DRIVER))
 		pr_info("stream link to 0x%08x @ 0x%08x %p\n",
 			return_target,
 			etnaviv_cmdbuf_get_va(cmdbuf, &gpu->mmu_context->cmdbuf_mapping),
 			cmdbuf->vaddr);
 
-	if (drm_debug_enabled(DRM_UT_DRIVER)) {
+	if (drm_debug_syslog_enabled(DRM_UT_DRIVER)) {
 		print_hex_dump(KERN_INFO, "cmd ", DUMP_PREFIX_OFFSET, 16, 4,
 			       cmdbuf->vaddr, cmdbuf->size, 0);
 
@@ -534,6 +534,6 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
 				    VIV_FE_LINK_HEADER_PREFETCH(link_dwords),
 				    link_target);
 
-	if (drm_debug_enabled(DRM_UT_DRIVER))
+	if (drm_debug_syslog_enabled(DRM_UT_DRIVER))
 		etnaviv_buffer_dump(gpu, buffer, 0, 0x50);
 }
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 08/13] drm/nouveau: Change debug checks to specifically target syslog

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

Since the logs protected by these checks specifically target syslog,
use the new drm_debug_syslog_enabled() call to avoid triggering
these prints when only trace is enabled.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/nouveau/dispnv50/disp.h | 4 ++--
 drivers/gpu/drm/nouveau/nouveau_drv.h   | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.h b/drivers/gpu/drm/nouveau/dispnv50/disp.h
index 696e70a6b98b..d60602db2cf0 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.h
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.h
@@ -85,14 +85,14 @@ extern const u64 wndwc57e_modifiers[];
 
 #define evo_mthd(p, m, s) do {						\
 	const u32 _m = (m), _s = (s);					\
-	if (drm_debug_enabled(DRM_UT_KMS))				\
+	if (drm_debug_syslog_enabled(DRM_UT_KMS))				\
 		pr_err("%04x %d %s\n", _m, _s, __func__);		\
 	*((p)++) = ((_s << 18) | _m);					\
 } while(0)
 
 #define evo_data(p, d) do {						\
 	const u32 _d = (d);						\
-	if (drm_debug_enabled(DRM_UT_KMS))				\
+	if (drm_debug_syslog_enabled(DRM_UT_KMS))				\
 		pr_err("\t%08x\n", _d);					\
 	*((p)++) = _d;							\
 } while(0)
diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
index 2a6519737800..b916d1f456cd 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drv.h
+++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
@@ -257,11 +257,11 @@ void nouveau_drm_device_remove(struct drm_device *dev);
 #define NV_INFO(drm,f,a...) NV_PRINTK(info, &(drm)->client, f, ##a)
 
 #define NV_DEBUG(drm,f,a...) do {                                              \
-	if (drm_debug_enabled(DRM_UT_DRIVER))                                  \
+	if (drm_debug_syslog_enabled(DRM_UT_DRIVER))                                  \
 		NV_PRINTK(info, &(drm)->client, f, ##a);                       \
 } while(0)
 #define NV_ATOMIC(drm,f,a...) do {                                             \
-	if (drm_debug_enabled(DRM_UT_ATOMIC))                                  \
+	if (drm_debug_syslog_enabled(DRM_UT_ATOMIC))                                  \
 		NV_PRINTK(info, &(drm)->client, f, ##a);                       \
 } while(0)
 
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 09/13] drm/i915: Change infoframe debug checks to specify syslog

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

Since the logs protected by these checks specifically target syslog,
use the new drm_debug_syslog_enabled() call to avoid triggering
these prints when only trace is enabled.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/i915/display/intel_display.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index b16aca0fe5f0..de449755d1e5 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -12876,7 +12876,7 @@ static void
 intel_dump_infoframe(struct drm_i915_private *dev_priv,
 		     const union hdmi_infoframe *frame)
 {
-	if (!drm_debug_enabled(DRM_UT_KMS))
+	if (!drm_debug_syslog_enabled(DRM_UT_KMS))
 		return;
 
 	hdmi_infoframe_log(KERN_DEBUG, dev_priv->drm.dev, frame);
@@ -13519,7 +13519,7 @@ pipe_config_infoframe_mismatch(struct drm_i915_private *dev_priv,
 			       const union hdmi_infoframe *b)
 {
 	if (fastset) {
-		if (!drm_debug_enabled(DRM_UT_KMS))
+		if (!drm_debug_syslog_enabled(DRM_UT_KMS))
 			return;
 
 		drm_dbg_kms(&dev_priv->drm,
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 10/13] drm/print: Add drm_debug_category_printer

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

This patch adds a new printer which will select the appropriate output
for a given debug category. Currently there is only one output target,
which is syslog. However in the future we'll have tracefs and it will be
useful to print to syslog, tracefs, or both. Drivers just need to create
the printer for the appropriate category and the printer will decide
where to send the output.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/drm_print.c |  5 +++++
 include/drm/drm_print.h     | 28 ++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 2ff7a6ecc632..4d984a01b3a3 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -172,6 +172,11 @@ void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_err);
 
+void __drm_printfn_noop(struct drm_printer *p, struct va_format *vaf)
+{
+}
+EXPORT_SYMBOL(__drm_printfn_noop);
+
 /**
  * drm_puts - print a const string to a &drm_printer stream
  * @p: the &drm printer
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index ce7675bf0d2b..8987b98bbfda 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -87,6 +87,7 @@ void __drm_puts_seq_file(struct drm_printer *p, const char *str);
 void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_noop(struct drm_printer *p, struct va_format *vaf);
 
 __printf(2, 3)
 void drm_printf(struct drm_printer *p, const char *f, ...);
@@ -329,6 +330,33 @@ static inline bool drm_debug_enabled(enum drm_debug_category category)
 	return drm_debug_syslog_enabled(category);
 }
 
+/**
+ * drm_debug_category_printer - construct a &drm_printer that outputs to
+ * pr_debug() if enabled for the given category.
+ * @category: the DRM_UT_* message category this message belongs to
+ * @prefix: trace output prefix
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer
+drm_debug_category_printer(enum drm_debug_category category,
+			   const char *prefix)
+{
+	struct drm_printer p = {
+		.prefix = prefix
+	};
+
+	if (drm_debug_syslog_enabled(category)) {
+		p.printfn = __drm_printfn_debug_syslog;
+	} else {
+		WARN(1, "Debug category %d is inactive.", category);
+		p.printfn = __drm_printfn_noop;
+	}
+
+	return p;
+}
+
 /*
  * struct device based logging
  *
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 11/13] drm/mst: Convert debug printers to debug category printers

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

The printers in dp_mst are meant to be gated on DRM_UT_DP, so use the
debug category printer to avoid dumping mst transactions to the wrong
place.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 1bdf3cfeeebb..e225a84da96e 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1203,7 +1203,8 @@ static int drm_dp_mst_wait_tx_reply(struct drm_dp_mst_branch *mstb,
 	}
 out:
 	if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
-		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+		struct drm_printer p = drm_debug_category_printer(DRM_UT_DP,
+								  DBG_PREFIX);
 
 		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
 	}
@@ -2739,7 +2740,8 @@ static int process_single_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
 
 	ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
 	if (unlikely(ret) && drm_debug_enabled(DRM_UT_DP)) {
-		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+		struct drm_printer p = drm_debug_category_printer(DRM_UT_DP,
+								  DBG_PREFIX);
 
 		drm_printf(&p, "sideband msg failed to send\n");
 		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
@@ -2783,7 +2785,8 @@ static void drm_dp_queue_down_tx(struct drm_dp_mst_topology_mgr *mgr,
 	list_add_tail(&txmsg->next, &mgr->tx_msg_downq);
 
 	if (drm_debug_enabled(DRM_UT_DP)) {
-		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+		struct drm_printer p = drm_debug_category_printer(DRM_UT_DP,
+								  DBG_PREFIX);
 
 		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
 	}
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 12/13] drm/i915: Use debug category printer for welcome message

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

The welcome printer is meant to be gated on DRM_UT_DRIVER, so use the
debug category printer to avoid dumping the message in the wrong
place.

Signed-off-by: Sean Paul <seanpaul@chromium.org>

Changes in v5:
-Added to the set
---
 drivers/gpu/drm/i915/i915_drv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 34ee12f3f02d..966212805ef7 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -876,7 +876,8 @@ static void i915_driver_unregister(struct drm_i915_private *dev_priv)
 static void i915_welcome_messages(struct drm_i915_private *dev_priv)
 {
 	if (drm_debug_enabled(DRM_UT_DRIVER)) {
-		struct drm_printer p = drm_debug_printer("i915 device info:");
+		struct drm_printer p = drm_debug_category_printer(DRM_UT_DRIVER,
+						"i915 device info:");
 
 		drm_printf(&p, "pciid=0x%04x rev=0x%02x platform=%s (subplatform=0x%x) gen=%i\n",
 			   INTEL_DEVID(dev_priv),
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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[PATCH v5 13/13] drm/print: Add tracefs support to the drm logging helpers

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

This patch adds a new module parameter called drm.trace which accepts
the same mask as drm.debug. When a debug category is enabled, log
messages will be put in a new tracefs instance called drm for
consumption.

Using the new tracefs instance will allow distros to enable drm logging
in production without impacting performance or spamming the system
logs.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3
Link: https://patchwork.freedesktop.org/patch/msgid/20200114172155.215463-1-sean@poorly.run #v4

Changes in v5:
-Re-write to use trace_array and the tracefs instance support
---
 Documentation/gpu/drm-uapi.rst |   6 +
 drivers/gpu/drm/drm_drv.c      |   3 +
 drivers/gpu/drm/drm_print.c    | 209 ++++++++++++++++++++++++++++-----
 include/drm/drm_print.h        |  63 ++++++++--
 4 files changed, 241 insertions(+), 40 deletions(-)

diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 56fec6ed1ad8..1c1c4d043f40 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -312,6 +312,12 @@ Debugfs Support
 .. kernel-doc:: drivers/gpu/drm/drm_debugfs.c
    :export:
 
+DRM Tracing
+---------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_print.c
+   :doc: DRM Tracing
+
 Sysfs Support
 =============
 
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index bc38322f306e..88404af74c9b 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -1108,12 +1108,15 @@ static void drm_core_exit(void)
 	drm_sysfs_destroy();
 	idr_destroy(&drm_minors_idr);
 	drm_connector_ida_destroy();
+	drm_trace_cleanup();
 }
 
 static int __init drm_core_init(void)
 {
 	int ret;
 
+	drm_trace_init();
+
 	drm_connector_ida_init();
 	idr_init(&drm_minors_idr);
 
diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 4d984a01b3a3..c4bef38921db 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -31,6 +31,7 @@
 #include <linux/moduleparam.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
+#include <linux/trace.h>
 
 #include <drm/drm.h>
 #include <drm/drm_drv.h>
@@ -43,17 +44,34 @@
 unsigned int __drm_debug_syslog;
 EXPORT_SYMBOL(__drm_debug_syslog);
 
-MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n"
-"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n"
-"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n"
-"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n"
-"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n"
-"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n"
-"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
-"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
-"\t\tBit 8 (0x100) will enable DP messages (displayport code)");
+/*
+ * __drm_debug_trace: Enable debug output in drm tracing instance.
+ * Bitmask of DRM_UT_x. See include/drm/drm_print.h for details.
+ */
+unsigned int __drm_debug_trace;
+EXPORT_SYMBOL(__drm_debug_trace);
+
+#define DEBUG_PARM_DESC(dst) \
+"Enable debug output to " dst ", where each bit enables a debug category.\n" \
+"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n" \
+"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n" \
+"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n" \
+"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n" \
+"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n" \
+"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n" \
+"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n" \
+"\t\tBit 8 (0x100) will enable DP messages (displayport code)"
+
+MODULE_PARM_DESC(debug, DEBUG_PARM_DESC("syslog"));
 module_param_named(debug, __drm_debug_syslog, int, 0600);
 
+MODULE_PARM_DESC(trace, DEBUG_PARM_DESC("tracefs"));
+module_param_named(trace, __drm_debug_trace, int, 0600);
+
+#ifdef CONFIG_TRACING
+struct trace_array *trace_arr;
+#endif
+
 void __drm_puts_coredump(struct drm_printer *p, const char *str)
 {
 	struct drm_print_iterator *iterator = p->arg;
@@ -166,6 +184,20 @@ void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_debug_syslog);
 
+void __drm_printfn_trace(struct drm_printer *p, struct va_format *vaf)
+{
+	drm_trace_printf("%s %pV", p->prefix, vaf);
+}
+EXPORT_SYMBOL(__drm_printfn_trace);
+
+void __drm_printfn_debug_syslog_and_trace(struct drm_printer *p,
+					   struct va_format *vaf)
+{
+	pr_debug("%s %pV", p->prefix, vaf);
+	drm_trace_printf("%s %pV", p->prefix, vaf);
+}
+EXPORT_SYMBOL(__drm_printfn_debug_syslog_and_trace);
+
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
 {
 	pr_err("*ERROR* %s %pV", p->prefix, vaf);
@@ -246,6 +278,14 @@ void drm_dev_printk(const struct device *dev, const char *level,
 	struct va_format vaf;
 	va_list args;
 
+	va_start(args, format);
+	vaf.fmt = format;
+	vaf.va = &args;
+	drm_trace_printf("%s%s[" DRM_NAME ":%ps] %pV",
+			 dev ? dev_name(dev) : "",dev ? " " : "",
+			 __builtin_return_address(0), &vaf);
+	va_end(args);
+
 	va_start(args, format);
 	vaf.fmt = format;
 	vaf.va = &args;
@@ -267,21 +307,30 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 	struct va_format vaf;
 	va_list args;
 
-	if (!drm_debug_enabled(category))
-		return;
+	if (drm_debug_syslog_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
 
-	va_start(args, format);
-	vaf.fmt = format;
-	vaf.va = &args;
+		if (dev)
+			dev_printk(KERN_DEBUG, dev, "[" DRM_NAME ":%ps] %pV",
+				__builtin_return_address(0), &vaf);
+		else
+			printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
+			__builtin_return_address(0), &vaf);
 
-	if (dev)
-		dev_printk(KERN_DEBUG, dev, "[" DRM_NAME ":%ps] %pV",
-			   __builtin_return_address(0), &vaf);
-	else
-		printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
-		       __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 
-	va_end(args);
+	if (drm_debug_trace_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
+		drm_trace_printf("%s%s[" DRM_NAME ":%ps] %pV",
+				 dev ? dev_name(dev) : "", dev ? " " : "",
+				 __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 }
 EXPORT_SYMBOL(drm_dev_dbg);
 
@@ -290,17 +339,25 @@ void __drm_dbg(enum drm_debug_category category, const char *format, ...)
 	struct va_format vaf;
 	va_list args;
 
-	if (!drm_debug_enabled(category))
-		return;
+	if (drm_debug_syslog_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
 
-	va_start(args, format);
-	vaf.fmt = format;
-	vaf.va = &args;
+		printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
+		__builtin_return_address(0), &vaf);
 
-	printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
-	       __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 
-	va_end(args);
+	if (drm_debug_trace_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
+		drm_trace_printf("[" DRM_NAME ":%ps] %pV",
+				 __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 }
 EXPORT_SYMBOL(__drm_dbg);
 
@@ -347,3 +404,97 @@ void drm_print_regset32(struct drm_printer *p, struct debugfs_regset32 *regset)
 	}
 }
 EXPORT_SYMBOL(drm_print_regset32);
+
+
+/**
+ * DOC: DRM Tracing
+ *
+ * *tl;dr* DRM tracing is a lightweight alternative to traditional DRM debug
+ * logging.
+ *
+ * While DRM logging is quite convenient when reproducing a specific issue, it
+ * doesn't help when something goes wrong unexpectedly. There are a couple
+ * reasons why one does not want to enable DRM logging at all times:
+ *
+ * 1. We don't want to overwhelm syslog with drm spam, others have to use it too
+ * 2. Console logging is slow
+ *
+ * DRM tracing aims to solve both these problems.
+ *
+ * To use DRM tracing, set the drm.trace module parameter (via cmdline or sysfs)
+ * to a DRM debug category mask (this is a bitmask of &drm_debug_category
+ * values):
+ * ::
+ *
+ *    eg: echo 0x106 > /sys/module/drm/parameters/trace
+ *
+ * Once active, all log messages in the specified categories will be written to
+ * the DRM trace. Once at capacity, the trace will overwrite old messages with
+ * new ones. At any point, one can read the trace file to extract the previous N
+ * DRM messages:
+ * ::
+ *
+ *    eg: cat /sys/kernel/tracing/instances/drm/trace
+ *
+ * Considerations
+ * **************
+ * The trace is subsystem wide, so if you have multiple devices active, they
+ * will be adding logs to the same trace.
+ *
+ * The contents of the DRM Trace are **not** considered UABI. **DO NOT depend on
+ * the values of these traces in your userspace.** These traces are intended for
+ * entertainment purposes only. The contents of these logs carry no warranty,
+ * expressed or implied.
+ */
+
+
+#ifdef CONFIG_TRACING
+
+/**
+ * drm_trace_init - initializes the drm trace array
+ *
+ * This function fetches (or creates) the drm trace array. This should be called
+ * once on drm subsystem creation and matched with drm_trace_cleanup().
+ */
+void drm_trace_init()
+{
+	trace_arr = trace_array_get_by_name("drm");
+	if (!trace_arr)
+		return;
+}
+EXPORT_SYMBOL(drm_trace_init);
+
+/**
+ * drm_trace_printf - adds an entry to the drm tracefs instance
+ * @format: printf format of the message to add to the trace
+ *
+ * This function adds a new entry in the drm tracefs instance
+ */
+void drm_trace_printf(const char *format, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	va_start(args, format);
+	vaf.fmt = format;
+	vaf.va = &args;
+	trace_array_printk(trace_arr, _THIS_IP_, "%pV", &vaf);
+	va_end(args);
+}
+
+/**
+ * drm_trace_cleanup - destroys the drm trace array
+ *
+ * This function destroys the drm trace array created with drm_trace_init. This
+ * should be called once on drm subsystem close and matched with
+ * drm_trace_init().
+ */
+void drm_trace_cleanup()
+{
+	if (trace_arr) {
+		trace_array_put(trace_arr);
+		trace_array_destroy(trace_arr);
+	}
+}
+EXPORT_SYMBOL(drm_trace_cleanup);
+#endif
\ No newline at end of file
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index 8987b98bbfda..284f7d325056 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -36,12 +36,13 @@
 
 /* Do *not* use outside of drm_print.[ch]! */
 extern unsigned int __drm_debug_syslog;
+extern unsigned int __drm_debug_trace;
 
 /**
  * DOC: print
  *
  * A simple wrapper for dev_printk(), seq_printf(), etc.  Allows same
- * debug code to be used for both debugfs and printk logging.
+ * debug code to be used for debugfs, printk and tracefs logging.
  *
  * For example::
  *
@@ -86,6 +87,9 @@ void __drm_printfn_seq_file(struct drm_printer *p, struct va_format *vaf);
 void __drm_puts_seq_file(struct drm_printer *p, const char *str);
 void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_trace(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_debug_syslog_and_trace(struct drm_printer *p,
+					   struct va_format *vaf);
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_noop(struct drm_printer *p, struct va_format *vaf);
 
@@ -219,7 +223,8 @@ static inline struct drm_printer drm_info_printer(struct device *dev)
 }
 
 /**
- * drm_debug_printer - construct a &drm_printer that outputs to pr_debug()
+ * drm_debug_printer - construct a &drm_printer that outputs to pr_debug() and
+ * drm tracefs
  * @prefix: debug output prefix
  *
  * RETURNS:
@@ -228,7 +233,7 @@ static inline struct drm_printer drm_info_printer(struct device *dev)
 static inline struct drm_printer drm_debug_printer(const char *prefix)
 {
 	struct drm_printer p = {
-		.printfn = __drm_printfn_debug_syslog,
+		.printfn = __drm_printfn_debug_syslog_and_trace,
 		.prefix = prefix
 	};
 	return p;
@@ -254,14 +259,14 @@ static inline struct drm_printer drm_err_printer(const char *prefix)
  * enum drm_debug_category - The DRM debug categories
  *
  * Each of the DRM debug logging macros use a specific category, and the logging
- * is filtered by the drm.debug module parameter. This enum specifies the values
- * for the interface.
+ * is filtered by the drm.debug and drm.trace module parameters. This enum
+ * specifies the values for the interface.
  *
  * Each DRM_DEBUG_<CATEGORY> macro logs to DRM_UT_<CATEGORY> category, except
  * DRM_DEBUG() logs to DRM_UT_CORE.
  *
- * Enabling verbose debug messages is done through the drm.debug parameter, each
- * category being enabled by a bit:
+ * Enabling verbose debug messages is done through the drm.debug and drm.trace
+ * parameters, each category being enabled by a bit:
  *
  *  - drm.debug=0x1 will enable CORE messages
  *  - drm.debug=0x2 will enable DRIVER messages
@@ -270,10 +275,14 @@ static inline struct drm_printer drm_err_printer(const char *prefix)
  *  - drm.debug=0x1ff will enable all messages
  *
  * An interesting feature is that it's possible to enable verbose logging at
- * run-time by echoing the debug value in its sysfs node::
+ * run-time by echoing the debug category value in its sysfs node::
  *
+ *   # For syslog logging:
  *   # echo 0xf > /sys/module/drm/parameters/debug
  *
+ *   # For tracefs logging:
+ *   # echo 0xf > /sys/module/drm/parameters/trace
+ *
  */
 enum drm_debug_category {
 	/**
@@ -325,14 +334,20 @@ static inline bool drm_debug_syslog_enabled(enum drm_debug_category category)
 	return unlikely(__drm_debug_syslog & category);
 }
 
+static inline bool drm_debug_trace_enabled(enum drm_debug_category category)
+{
+	return unlikely(__drm_debug_trace & category);
+}
+
 static inline bool drm_debug_enabled(enum drm_debug_category category)
 {
-	return drm_debug_syslog_enabled(category);
+	return drm_debug_syslog_enabled(category) ||
+	       drm_debug_trace_enabled(category);
 }
 
 /**
  * drm_debug_category_printer - construct a &drm_printer that outputs to
- * pr_debug() if enabled for the given category.
+ * pr_debug() and/or the drm tracefs instance if enabled for the given category.
  * @category: the DRM_UT_* message category this message belongs to
  * @prefix: trace output prefix
  *
@@ -347,8 +362,13 @@ drm_debug_category_printer(enum drm_debug_category category,
 		.prefix = prefix
 	};
 
-	if (drm_debug_syslog_enabled(category)) {
+	if (drm_debug_syslog_enabled(category) &&
+	    drm_debug_trace_enabled(category)) {
+		p.printfn = __drm_printfn_debug_syslog_and_trace;
+	} else if (drm_debug_syslog_enabled(category)) {
 		p.printfn = __drm_printfn_debug_syslog;
+	} else if (drm_debug_trace_enabled(category)) {
+		p.printfn = __drm_printfn_trace;
 	} else {
 		WARN(1, "Debug category %d is inactive.", category);
 		p.printfn = __drm_printfn_noop;
@@ -357,6 +377,27 @@ drm_debug_category_printer(enum drm_debug_category category,
 	return p;
 }
 
+
+#ifdef CONFIG_TRACING
+void drm_trace_init(void);
+__printf(1, 2)
+void drm_trace_printf(const char *format, ...);
+void drm_trace_cleanup(void);
+#else
+static inline void drm_trace_init(void)
+{
+}
+
+__printf(1, 2)
+static inline void drm_trace_printf(const char *format, ...)
+{
+}
+
+static inline void drm_trace_cleanup(void)
+{
+}
+#endif
+
 /*
  * struct device based logging
  *
-- 
Sean Paul, Software Engineer, Google / Chromium OS

_______________________________________________
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Re: [PATCH v5 13/13] drm/print: Add tracefs support to the drm logging helpers

[kernel test robot]

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Hi Sean,

I love your patch! Perhaps something to improve:

[auto build test WARNING on drm-intel/for-linux-next]
[also build test WARNING on drm-exynos/exynos-drm-next tegra-drm/drm/tegra/for-next drm-tip/drm-tip linus/master v5.7]
[cannot apply to drm/drm-next]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Sean-Paul/drm-trace-Mirror-DRM-debug-logs-to-tracefs/20200609-050750
base:   git://anongit.freedesktop.org/drm-intel for-linux-next
config: riscv-allyesconfig (attached as .config)
compiler: riscv64-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=riscv 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>, old ones prefixed by <<):

drivers/gpu/drm/drm_print.c: In function 'drm_trace_init':
>> drivers/gpu/drm/drm_print.c:459:6: warning: old-style function definition [-Wold-style-definition]
459 | void drm_trace_init()
|      ^~~~~~~~~~~~~~
drivers/gpu/drm/drm_print.c: In function 'drm_trace_cleanup':
drivers/gpu/drm/drm_print.c:492:6: warning: old-style function definition [-Wold-style-definition]
492 | void drm_trace_cleanup()
|      ^~~~~~~~~~~~~~~~~

vim +459 drivers/gpu/drm/drm_print.c

   452	
   453	/**
   454	 * drm_trace_init - initializes the drm trace array
   455	 *
   456	 * This function fetches (or creates) the drm trace array. This should be called
   457	 * once on drm subsystem creation and matched with drm_trace_cleanup().
   458	 */
 > 459	void drm_trace_init()
   460	{
   461		trace_arr = trace_array_get_by_name("drm");
   462		if (!trace_arr)
   463			return;
   464	}
   465	EXPORT_SYMBOL(drm_trace_init);
   466	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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_______________________________________________
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Re: [PATCH v5 13/13] drm/print: Add tracefs support to the drm logging helpers

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 2949 bytes --]

Hi Sean,

I love your patch! Perhaps something to improve:

[auto build test WARNING on drm-intel/for-linux-next]
[also build test WARNING on drm-exynos/exynos-drm-next tegra-drm/drm/tegra/for-next drm-tip/drm-tip linus/master v5.7 next-20200608]
[cannot apply to drm/drm-next]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Sean-Paul/drm-trace-Mirror-DRM-debug-logs-to-tracefs/20200609-050750
base:   git://anongit.freedesktop.org/drm-intel for-linux-next
config: x86_64-randconfig-s021-20200607 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-13) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.1-247-gcadbd124-dirty
        # save the attached .config to linux build tree
        make W=1 C=1 ARCH=x86_64 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)

>> drivers/gpu/drm/drm_print.c:459:21: sparse: sparse: non-ANSI function declaration of function 'drm_trace_init'
>> drivers/gpu/drm/drm_print.c:492:24: sparse: sparse: non-ANSI function declaration of function 'drm_trace_cleanup'

Please review and possibly fold the followup patch.

vim +/drm_trace_init +459 drivers/gpu/drm/drm_print.c

   452	
   453	/**
   454	 * drm_trace_init - initializes the drm trace array
   455	 *
   456	 * This function fetches (or creates) the drm trace array. This should be called
   457	 * once on drm subsystem creation and matched with drm_trace_cleanup().
   458	 */
 > 459	void drm_trace_init()
   460	{
   461		trace_arr = trace_array_get_by_name("drm");
   462		if (!trace_arr)
   463			return;
   464	}
   465	EXPORT_SYMBOL(drm_trace_init);
   466	
   467	/**
   468	 * drm_trace_printf - adds an entry to the drm tracefs instance
   469	 * @format: printf format of the message to add to the trace
   470	 *
   471	 * This function adds a new entry in the drm tracefs instance
   472	 */
   473	void drm_trace_printf(const char *format, ...)
   474	{
   475		struct va_format vaf;
   476		va_list args;
   477	
   478		va_start(args, format);
   479		vaf.fmt = format;
   480		vaf.va = &args;
   481		trace_array_printk(trace_arr, _THIS_IP_, "%pV", &vaf);
   482		va_end(args);
   483	}
   484	
   485	/**
   486	 * drm_trace_cleanup - destroys the drm trace array
   487	 *
   488	 * This function destroys the drm trace array created with drm_trace_init. This
   489	 * should be called once on drm subsystem close and matched with
   490	 * drm_trace_init().
   491	 */
 > 492	void drm_trace_cleanup()

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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[PATCH v6 13/13] drm/print: Add tracefs support to the drm logging helpers

[Sean Paul]

From: Sean Paul <seanpaul@chromium.org>

This patch adds a new module parameter called drm.trace which accepts
the same mask as drm.debug. When a debug category is enabled, log
messages will be put in a new tracefs instance called drm for
consumption.

Using the new tracefs instance will allow distros to enable drm logging
in production without impacting performance or spamming the system
logs.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3
Link: https://patchwork.freedesktop.org/patch/msgid/20200114172155.215463-1-sean@poorly.run #v4

Changes in v5:
-Re-write to use trace_array and the tracefs instance support

Changes in v6:
-Fix old-style function definition warnings
Reported-by: kernel test robot <lkp@intel.com>
---
 Documentation/gpu/drm-uapi.rst |   6 +
 drivers/gpu/drm/drm_drv.c      |   3 +
 drivers/gpu/drm/drm_print.c    | 209 ++++++++++++++++++++++++++++-----
 include/drm/drm_print.h        |  63 ++++++++--
 4 files changed, 241 insertions(+), 40 deletions(-)

diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 56fec6ed1ad8..1c1c4d043f40 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -312,6 +312,12 @@ Debugfs Support
 .. kernel-doc:: drivers/gpu/drm/drm_debugfs.c
    :export:
 
+DRM Tracing
+---------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_print.c
+   :doc: DRM Tracing
+
 Sysfs Support
 =============
 
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index bc38322f306e..88404af74c9b 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -1108,12 +1108,15 @@ static void drm_core_exit(void)
 	drm_sysfs_destroy();
 	idr_destroy(&drm_minors_idr);
 	drm_connector_ida_destroy();
+	drm_trace_cleanup();
 }
 
 static int __init drm_core_init(void)
 {
 	int ret;
 
+	drm_trace_init();
+
 	drm_connector_ida_init();
 	idr_init(&drm_minors_idr);
 
diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 4d984a01b3a3..18dfbd43c23b 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -31,6 +31,7 @@
 #include <linux/moduleparam.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
+#include <linux/trace.h>
 
 #include <drm/drm.h>
 #include <drm/drm_drv.h>
@@ -43,17 +44,34 @@
 unsigned int __drm_debug_syslog;
 EXPORT_SYMBOL(__drm_debug_syslog);
 
-MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n"
-"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n"
-"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n"
-"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n"
-"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n"
-"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n"
-"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
-"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
-"\t\tBit 8 (0x100) will enable DP messages (displayport code)");
+/*
+ * __drm_debug_trace: Enable debug output in drm tracing instance.
+ * Bitmask of DRM_UT_x. See include/drm/drm_print.h for details.
+ */
+unsigned int __drm_debug_trace;
+EXPORT_SYMBOL(__drm_debug_trace);
+
+#define DEBUG_PARM_DESC(dst) \
+"Enable debug output to " dst ", where each bit enables a debug category.\n" \
+"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n" \
+"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n" \
+"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n" \
+"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n" \
+"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n" \
+"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n" \
+"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n" \
+"\t\tBit 8 (0x100) will enable DP messages (displayport code)"
+
+MODULE_PARM_DESC(debug, DEBUG_PARM_DESC("syslog"));
 module_param_named(debug, __drm_debug_syslog, int, 0600);
 
+MODULE_PARM_DESC(trace, DEBUG_PARM_DESC("tracefs"));
+module_param_named(trace, __drm_debug_trace, int, 0600);
+
+#ifdef CONFIG_TRACING
+struct trace_array *trace_arr;
+#endif
+
 void __drm_puts_coredump(struct drm_printer *p, const char *str)
 {
 	struct drm_print_iterator *iterator = p->arg;
@@ -166,6 +184,20 @@ void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_debug_syslog);
 
+void __drm_printfn_trace(struct drm_printer *p, struct va_format *vaf)
+{
+	drm_trace_printf("%s %pV", p->prefix, vaf);
+}
+EXPORT_SYMBOL(__drm_printfn_trace);
+
+void __drm_printfn_debug_syslog_and_trace(struct drm_printer *p,
+					   struct va_format *vaf)
+{
+	pr_debug("%s %pV", p->prefix, vaf);
+	drm_trace_printf("%s %pV", p->prefix, vaf);
+}
+EXPORT_SYMBOL(__drm_printfn_debug_syslog_and_trace);
+
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
 {
 	pr_err("*ERROR* %s %pV", p->prefix, vaf);
@@ -246,6 +278,14 @@ void drm_dev_printk(const struct device *dev, const char *level,
 	struct va_format vaf;
 	va_list args;
 
+	va_start(args, format);
+	vaf.fmt = format;
+	vaf.va = &args;
+	drm_trace_printf("%s%s[" DRM_NAME ":%ps] %pV",
+			 dev ? dev_name(dev) : "",dev ? " " : "",
+			 __builtin_return_address(0), &vaf);
+	va_end(args);
+
 	va_start(args, format);
 	vaf.fmt = format;
 	vaf.va = &args;
@@ -267,21 +307,30 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 	struct va_format vaf;
 	va_list args;
 
-	if (!drm_debug_enabled(category))
-		return;
+	if (drm_debug_syslog_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
 
-	va_start(args, format);
-	vaf.fmt = format;
-	vaf.va = &args;
+		if (dev)
+			dev_printk(KERN_DEBUG, dev, "[" DRM_NAME ":%ps] %pV",
+				__builtin_return_address(0), &vaf);
+		else
+			printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
+			__builtin_return_address(0), &vaf);
 
-	if (dev)
-		dev_printk(KERN_DEBUG, dev, "[" DRM_NAME ":%ps] %pV",
-			   __builtin_return_address(0), &vaf);
-	else
-		printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
-		       __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 
-	va_end(args);
+	if (drm_debug_trace_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
+		drm_trace_printf("%s%s[" DRM_NAME ":%ps] %pV",
+				 dev ? dev_name(dev) : "", dev ? " " : "",
+				 __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 }
 EXPORT_SYMBOL(drm_dev_dbg);
 
@@ -290,17 +339,25 @@ void __drm_dbg(enum drm_debug_category category, const char *format, ...)
 	struct va_format vaf;
 	va_list args;
 
-	if (!drm_debug_enabled(category))
-		return;
+	if (drm_debug_syslog_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
 
-	va_start(args, format);
-	vaf.fmt = format;
-	vaf.va = &args;
+		printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
+		__builtin_return_address(0), &vaf);
 
-	printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
-	       __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 
-	va_end(args);
+	if (drm_debug_trace_enabled(category)) {
+		va_start(args, format);
+		vaf.fmt = format;
+		vaf.va = &args;
+		drm_trace_printf("[" DRM_NAME ":%ps] %pV",
+				 __builtin_return_address(0), &vaf);
+		va_end(args);
+	}
 }
 EXPORT_SYMBOL(__drm_dbg);
 
@@ -347,3 +404,97 @@ void drm_print_regset32(struct drm_printer *p, struct debugfs_regset32 *regset)
 	}
 }
 EXPORT_SYMBOL(drm_print_regset32);
+
+
+/**
+ * DOC: DRM Tracing
+ *
+ * *tl;dr* DRM tracing is a lightweight alternative to traditional DRM debug
+ * logging.
+ *
+ * While DRM logging is quite convenient when reproducing a specific issue, it
+ * doesn't help when something goes wrong unexpectedly. There are a couple
+ * reasons why one does not want to enable DRM logging at all times:
+ *
+ * 1. We don't want to overwhelm syslog with drm spam, others have to use it too
+ * 2. Console logging is slow
+ *
+ * DRM tracing aims to solve both these problems.
+ *
+ * To use DRM tracing, set the drm.trace module parameter (via cmdline or sysfs)
+ * to a DRM debug category mask (this is a bitmask of &drm_debug_category
+ * values):
+ * ::
+ *
+ *    eg: echo 0x106 > /sys/module/drm/parameters/trace
+ *
+ * Once active, all log messages in the specified categories will be written to
+ * the DRM trace. Once at capacity, the trace will overwrite old messages with
+ * new ones. At any point, one can read the trace file to extract the previous N
+ * DRM messages:
+ * ::
+ *
+ *    eg: cat /sys/kernel/tracing/instances/drm/trace
+ *
+ * Considerations
+ * **************
+ * The trace is subsystem wide, so if you have multiple devices active, they
+ * will be adding logs to the same trace.
+ *
+ * The contents of the DRM Trace are **not** considered UABI. **DO NOT depend on
+ * the values of these traces in your userspace.** These traces are intended for
+ * entertainment purposes only. The contents of these logs carry no warranty,
+ * expressed or implied.
+ */
+
+
+#ifdef CONFIG_TRACING
+
+/**
+ * drm_trace_init - initializes the drm trace array
+ *
+ * This function fetches (or creates) the drm trace array. This should be called
+ * once on drm subsystem creation and matched with drm_trace_cleanup().
+ */
+void drm_trace_init(void)
+{
+	trace_arr = trace_array_get_by_name("drm");
+	if (!trace_arr)
+		return;
+}
+EXPORT_SYMBOL(drm_trace_init);
+
+/**
+ * drm_trace_printf - adds an entry to the drm tracefs instance
+ * @format: printf format of the message to add to the trace
+ *
+ * This function adds a new entry in the drm tracefs instance
+ */
+void drm_trace_printf(const char *format, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	va_start(args, format);
+	vaf.fmt = format;
+	vaf.va = &args;
+	trace_array_printk(trace_arr, _THIS_IP_, "%pV", &vaf);
+	va_end(args);
+}
+
+/**
+ * drm_trace_cleanup - destroys the drm trace array
+ *
+ * This function destroys the drm trace array created with drm_trace_init. This
+ * should be called once on drm subsystem close and matched with
+ * drm_trace_init().
+ */
+void drm_trace_cleanup(void)
+{
+	if (trace_arr) {
+		trace_array_put(trace_arr);
+		trace_array_destroy(trace_arr);
+	}
+}
+EXPORT_SYMBOL(drm_trace_cleanup);
+#endif
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index 8987b98bbfda..284f7d325056 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -36,12 +36,13 @@
 
 /* Do *not* use outside of drm_print.[ch]! */
 extern unsigned int __drm_debug_syslog;
+extern unsigned int __drm_debug_trace;
 
 /**
  * DOC: print
  *
  * A simple wrapper for dev_printk(), seq_printf(), etc.  Allows same
- * debug code to be used for both debugfs and printk logging.
+ * debug code to be used for debugfs, printk and tracefs logging.
  *
  * For example::
  *
@@ -86,6 +87,9 @@ void __drm_printfn_seq_file(struct drm_printer *p, struct va_format *vaf);
 void __drm_puts_seq_file(struct drm_printer *p, const char *str);
 void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_trace(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_debug_syslog_and_trace(struct drm_printer *p,
+					   struct va_format *vaf);
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_noop(struct drm_printer *p, struct va_format *vaf);
 
@@ -219,7 +223,8 @@ static inline struct drm_printer drm_info_printer(struct device *dev)
 }
 
 /**
- * drm_debug_printer - construct a &drm_printer that outputs to pr_debug()
+ * drm_debug_printer - construct a &drm_printer that outputs to pr_debug() and
+ * drm tracefs
  * @prefix: debug output prefix
  *
  * RETURNS:
@@ -228,7 +233,7 @@ static inline struct drm_printer drm_info_printer(struct device *dev)
 static inline struct drm_printer drm_debug_printer(const char *prefix)
 {
 	struct drm_printer p = {
-		.printfn = __drm_printfn_debug_syslog,
+		.printfn = __drm_printfn_debug_syslog_and_trace,
 		.prefix = prefix
 	};
 	return p;
@@ -254,14 +259,14 @@ static inline struct drm_printer drm_err_printer(const char *prefix)
  * enum drm_debug_category - The DRM debug categories
  *
  * Each of the DRM debug logging macros use a specific category, and the logging
- * is filtered by the drm.debug module parameter. This enum specifies the values
- * for the interface.
+ * is filtered by the drm.debug and drm.trace module parameters. This enum
+ * specifies the values for the interface.
  *
  * Each DRM_DEBUG_<CATEGORY> macro logs to DRM_UT_<CATEGORY> category, except
  * DRM_DEBUG() logs to DRM_UT_CORE.
  *
- * Enabling verbose debug messages is done through the drm.debug parameter, each
- * category being enabled by a bit:
+ * Enabling verbose debug messages is done through the drm.debug and drm.trace
+ * parameters, each category being enabled by a bit:
  *
  *  - drm.debug=0x1 will enable CORE messages
  *  - drm.debug=0x2 will enable DRIVER messages
@@ -270,10 +275,14 @@ static inline struct drm_printer drm_err_printer(const char *prefix)
  *  - drm.debug=0x1ff will enable all messages
  *
  * An interesting feature is that it's possible to enable verbose logging at
- * run-time by echoing the debug value in its sysfs node::
+ * run-time by echoing the debug category value in its sysfs node::
  *
+ *   # For syslog logging:
  *   # echo 0xf > /sys/module/drm/parameters/debug
  *
+ *   # For tracefs logging:
+ *   # echo 0xf > /sys/module/drm/parameters/trace
+ *
  */
 enum drm_debug_category {
 	/**
@@ -325,14 +334,20 @@ static inline bool drm_debug_syslog_enabled(enum drm_debug_category category)
 	return unlikely(__drm_debug_syslog & category);
 }
 
+static inline bool drm_debug_trace_enabled(enum drm_debug_category category)
+{
+	return unlikely(__drm_debug_trace & category);
+}
+
 static inline bool drm_debug_enabled(enum drm_debug_category category)
 {
-	return drm_debug_syslog_enabled(category);
+	return drm_debug_syslog_enabled(category) ||
+	       drm_debug_trace_enabled(category);
 }
 
 /**
  * drm_debug_category_printer - construct a &drm_printer that outputs to
- * pr_debug() if enabled for the given category.
+ * pr_debug() and/or the drm tracefs instance if enabled for the given category.
  * @category: the DRM_UT_* message category this message belongs to
  * @prefix: trace output prefix
  *
@@ -347,8 +362,13 @@ drm_debug_category_printer(enum drm_debug_category category,
 		.prefix = prefix
 	};
 
-	if (drm_debug_syslog_enabled(category)) {
+	if (drm_debug_syslog_enabled(category) &&
+	    drm_debug_trace_enabled(category)) {
+		p.printfn = __drm_printfn_debug_syslog_and_trace;
+	} else if (drm_debug_syslog_enabled(category)) {
 		p.printfn = __drm_printfn_debug_syslog;
+	} else if (drm_debug_trace_enabled(category)) {
+		p.printfn = __drm_printfn_trace;
 	} else {
 		WARN(1, "Debug category %d is inactive.", category);
 		p.printfn = __drm_printfn_noop;
@@ -357,6 +377,27 @@ drm_debug_category_printer(enum drm_debug_category category,
 	return p;
 }
 
+
+#ifdef CONFIG_TRACING
+void drm_trace_init(void);
+__printf(1, 2)
+void drm_trace_printf(const char *format, ...);
+void drm_trace_cleanup(void);
+#else
+static inline void drm_trace_init(void)
+{
+}
+
+__printf(1, 2)
+static inline void drm_trace_printf(const char *format, ...)
+{
+}
+
+static inline void drm_trace_cleanup(void)
+{
+}
+#endif
+
 /*
  * struct device based logging
  *
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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Re: [PATCH v6 13/13] drm/print: Add tracefs support to the drm logging helpers

[Steven Rostedt]

On Tue,  9 Jun 2020 11:49:19 -0400
Sean Paul <sean@poorly.run> wrote:

> +/**
> + * drm_trace_printf - adds an entry to the drm tracefs instance
> + * @format: printf format of the message to add to the trace
> + *
> + * This function adds a new entry in the drm tracefs instance
> + */
> +void drm_trace_printf(const char *format, ...)
> +{
> +	struct va_format vaf;
> +	va_list args;
> +
> +	va_start(args, format);
> +	vaf.fmt = format;
> +	vaf.va = &args;
> +	trace_array_printk(trace_arr, _THIS_IP_, "%pV", &vaf);
> +	va_end(args);
> +}

The only issue I have with this patch is the above. I really dislike
the use of trace_array_print(), as that is made to be for debugging and
not something that should be in a production kernel.

Ideally, every instance should just pass the data it wants to record,
and you add it to a trace event. There's already a drm trace subsystem,
how would this be different. Perhaps create a drm_log subsystem, and
you only need to have your instance enable it?

I guess I'm still confused to why this is needed over just having trace
events? What's special about this case?

-- Steve

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Re: [PATCH v6 13/13] drm/print: Add tracefs support to the drm logging helpers

[Sean Paul]

On Wed, Jun 10, 2020 at 11:01 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Tue,  9 Jun 2020 11:49:19 -0400
> Sean Paul <sean@poorly.run> wrote:
>
> > +/**
> > + * drm_trace_printf - adds an entry to the drm tracefs instance
> > + * @format: printf format of the message to add to the trace
> > + *
> > + * This function adds a new entry in the drm tracefs instance
> > + */
> > +void drm_trace_printf(const char *format, ...)
> > +{
> > +     struct va_format vaf;
> > +     va_list args;
> > +
> > +     va_start(args, format);
> > +     vaf.fmt = format;
> > +     vaf.va = &args;
> > +     trace_array_printk(trace_arr, _THIS_IP_, "%pV", &vaf);
> > +     va_end(args);
> > +}
>
> The only issue I have with this patch is the above. I really dislike
> the use of trace_array_print(), as that is made to be for debugging and
> not something that should be in a production kernel.
>
> Ideally, every instance should just pass the data it wants to record,
> and you add it to a trace event. There's already a drm trace subsystem,
> how would this be different. Perhaps create a drm_log subsystem, and
> you only need to have your instance enable it?
>
> I guess I'm still confused to why this is needed over just having trace
> events? What's special about this case?
>

Hi Steve,
In v2 I had added trace events throughout drm in this manner. See
https://lists.freedesktop.org/archives/dri-devel/2019-November/243318.html

The feedback I received was that exposing the events in such a
structured way would bind us to the trace formats and make things more
difficult moving forward.

Aside from the UAPI concerns, wearing my ChromeOS hat (with full
knowledge that most upstream folks won't care about this), this
solution also misses on making problems easier to diagnose from
logs/user feedback. It requires that driver developers add tracing
beside their logging, and makes backporting upstream code even harder
than it is right now. If we can intercept the existing and new logging
at the source, it's much easier to ensure the flight recorder is
accurate. We've been shipping this (v4) in CrOS for ~months now and
it's been invaluable. With this experience in mind, I'd be really
hesitant to change course.

Sean

> -- Steve
>
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[RFC PATCH] drm/print: trace_arr can be static

[kernel test robot]

Signed-off-by: kernel test robot <lkp@intel.com>
---
 drm_print.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index c4bef38921db1..a50d0b24c911f 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -69,7 +69,7 @@ MODULE_PARM_DESC(trace, DEBUG_PARM_DESC("tracefs"));
 module_param_named(trace, __drm_debug_trace, int, 0600);
 
 #ifdef CONFIG_TRACING
-struct trace_array *trace_arr;
+static struct trace_array *trace_arr;
 #endif
 
 void __drm_puts_coredump(struct drm_printer *p, const char *str)
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Re: [PATCH v5 13/13] drm/print: Add tracefs support to the drm logging helpers

[Pekka Paalanen]

[-- Attachment #1.1: Type: text/plain, Size: 7248 bytes --]

On Mon,  8 Jun 2020 17:05:03 -0400
Sean Paul <sean@poorly.run> wrote:

> From: Sean Paul <seanpaul@chromium.org>
> 
> This patch adds a new module parameter called drm.trace which accepts
> the same mask as drm.debug. When a debug category is enabled, log
> messages will be put in a new tracefs instance called drm for
> consumption.
> 
> Using the new tracefs instance will allow distros to enable drm logging
> in production without impacting performance or spamming the system
> logs.
> 
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
> Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
> Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3
> Link: https://patchwork.freedesktop.org/patch/msgid/20200114172155.215463-1-sean@poorly.run #v4
> 
> Changes in v5:
> -Re-write to use trace_array and the tracefs instance support
> ---
>  Documentation/gpu/drm-uapi.rst |   6 +
>  drivers/gpu/drm/drm_drv.c      |   3 +
>  drivers/gpu/drm/drm_print.c    | 209 ++++++++++++++++++++++++++++-----
>  include/drm/drm_print.h        |  63 ++++++++--
>  4 files changed, 241 insertions(+), 40 deletions(-)
> 
> diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
> index 56fec6ed1ad8..1c1c4d043f40 100644
> --- a/Documentation/gpu/drm-uapi.rst
> +++ b/Documentation/gpu/drm-uapi.rst
> @@ -312,6 +312,12 @@ Debugfs Support
>  .. kernel-doc:: drivers/gpu/drm/drm_debugfs.c
>     :export:
>  
> +DRM Tracing
> +---------------
> +
> +.. kernel-doc:: drivers/gpu/drm/drm_print.c
> +   :doc: DRM Tracing
> +
>  Sysfs Support
>  =============
>  
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index bc38322f306e..88404af74c9b 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -1108,12 +1108,15 @@ static void drm_core_exit(void)
>  	drm_sysfs_destroy();
>  	idr_destroy(&drm_minors_idr);
>  	drm_connector_ida_destroy();
> +	drm_trace_cleanup();
>  }
>  
>  static int __init drm_core_init(void)
>  {
>  	int ret;
>  
> +	drm_trace_init();
> +
>  	drm_connector_ida_init();
>  	idr_init(&drm_minors_idr);
>  
> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> index 4d984a01b3a3..c4bef38921db 100644
> --- a/drivers/gpu/drm/drm_print.c
> +++ b/drivers/gpu/drm/drm_print.c
> @@ -31,6 +31,7 @@
>  #include <linux/moduleparam.h>
>  #include <linux/seq_file.h>
>  #include <linux/slab.h>
> +#include <linux/trace.h>
>  
>  #include <drm/drm.h>
>  #include <drm/drm_drv.h>
> @@ -43,17 +44,34 @@
>  unsigned int __drm_debug_syslog;
>  EXPORT_SYMBOL(__drm_debug_syslog);
>  
> -MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n"
> -"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n"
> -"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n"
> -"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n"
> -"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n"
> -"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n"
> -"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
> -"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
> -"\t\tBit 8 (0x100) will enable DP messages (displayport code)");
> +/*
> + * __drm_debug_trace: Enable debug output in drm tracing instance.
> + * Bitmask of DRM_UT_x. See include/drm/drm_print.h for details.
> + */
> +unsigned int __drm_debug_trace;
> +EXPORT_SYMBOL(__drm_debug_trace);

Hi!

Might distributions perhaps want to set a default value for this via
Kconfig? Or could setting it via sysfs happen early enough to diagnose
e.g. Plymouth problems?

Or maybe there is nothing to see from early boot?

The general usefulness of this feature depends on whether people
actually run with it enabled.

> +
> +#define DEBUG_PARM_DESC(dst) \
> +"Enable debug output to " dst ", where each bit enables a debug category.\n" \
> +"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n" \
> +"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n" \
> +"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n" \
> +"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n" \
> +"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n" \
> +"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n" \
> +"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n" \
> +"\t\tBit 8 (0x100) will enable DP messages (displayport code)"
> +
> +MODULE_PARM_DESC(debug, DEBUG_PARM_DESC("syslog"));
>  module_param_named(debug, __drm_debug_syslog, int, 0600);
>  
> +MODULE_PARM_DESC(trace, DEBUG_PARM_DESC("tracefs"));
> +module_param_named(trace, __drm_debug_trace, int, 0600);

...

> +
> +/**
> + * DOC: DRM Tracing
> + *
> + * *tl;dr* DRM tracing is a lightweight alternative to traditional DRM debug
> + * logging.
> + *
> + * While DRM logging is quite convenient when reproducing a specific issue, it
> + * doesn't help when something goes wrong unexpectedly. There are a couple
> + * reasons why one does not want to enable DRM logging at all times:
> + *
> + * 1. We don't want to overwhelm syslog with drm spam, others have to use it too
> + * 2. Console logging is slow
> + *
> + * DRM tracing aims to solve both these problems.
> + *
> + * To use DRM tracing, set the drm.trace module parameter (via cmdline or sysfs)
> + * to a DRM debug category mask (this is a bitmask of &drm_debug_category
> + * values):
> + * ::
> + *
> + *    eg: echo 0x106 > /sys/module/drm/parameters/trace
> + *
> + * Once active, all log messages in the specified categories will be written to
> + * the DRM trace. Once at capacity, the trace will overwrite old messages with
> + * new ones. At any point, one can read the trace file to extract the previous N
> + * DRM messages:
> + * ::
> + *
> + *    eg: cat /sys/kernel/tracing/instances/drm/trace
> + *
> + * Considerations
> + * **************
> + * The trace is subsystem wide, so if you have multiple devices active, they
> + * will be adding logs to the same trace.
> + *
> + * The contents of the DRM Trace are **not** considered UABI. **DO NOT depend on
> + * the values of these traces in your userspace.** These traces are intended for
> + * entertainment purposes only. The contents of these logs carry no warranty,
> + * expressed or implied.
> + */

Sounds good to me!
This part is:
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>


Thanks,
pq

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Re: [PATCH v5 13/13] drm/print: Add tracefs support to the drm logging helpers

[Sean Paul]

On Wed, Jun 10, 2020 at 3:57 AM Pekka Paalanen <ppaalanen@gmail.com> wrote:
>
> On Mon,  8 Jun 2020 17:05:03 -0400
> Sean Paul <sean@poorly.run> wrote:
>
> > From: Sean Paul <seanpaul@chromium.org>
> >
> > This patch adds a new module parameter called drm.trace which accepts
> > the same mask as drm.debug. When a debug category is enabled, log
> > messages will be put in a new tracefs instance called drm for
> > consumption.
> >
> > Using the new tracefs instance will allow distros to enable drm logging
> > in production without impacting performance or spamming the system
> > logs.
> >
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: David Airlie <airlied@gmail.com>
> > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Pekka Paalanen <ppaalanen@gmail.com>
> > Cc: Rob Clark <robdclark@gmail.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Signed-off-by: Sean Paul <seanpaul@chromium.org>
> > Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
> > Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
> > Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3
> > Link: https://patchwork.freedesktop.org/patch/msgid/20200114172155.215463-1-sean@poorly.run #v4
> >
> > Changes in v5:
> > -Re-write to use trace_array and the tracefs instance support
> > ---
> >  Documentation/gpu/drm-uapi.rst |   6 +
> >  drivers/gpu/drm/drm_drv.c      |   3 +
> >  drivers/gpu/drm/drm_print.c    | 209 ++++++++++++++++++++++++++++-----
> >  include/drm/drm_print.h        |  63 ++++++++--
> >  4 files changed, 241 insertions(+), 40 deletions(-)
> >
> > diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
> > index 56fec6ed1ad8..1c1c4d043f40 100644
> > --- a/Documentation/gpu/drm-uapi.rst
> > +++ b/Documentation/gpu/drm-uapi.rst
> > @@ -312,6 +312,12 @@ Debugfs Support
> >  .. kernel-doc:: drivers/gpu/drm/drm_debugfs.c
> >     :export:
> >
> > +DRM Tracing
> > +---------------
> > +
> > +.. kernel-doc:: drivers/gpu/drm/drm_print.c
> > +   :doc: DRM Tracing
> > +
> >  Sysfs Support
> >  =============
> >
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index bc38322f306e..88404af74c9b 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -1108,12 +1108,15 @@ static void drm_core_exit(void)
> >       drm_sysfs_destroy();
> >       idr_destroy(&drm_minors_idr);
> >       drm_connector_ida_destroy();
> > +     drm_trace_cleanup();
> >  }
> >
> >  static int __init drm_core_init(void)
> >  {
> >       int ret;
> >
> > +     drm_trace_init();
> > +
> >       drm_connector_ida_init();
> >       idr_init(&drm_minors_idr);
> >
> > diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> > index 4d984a01b3a3..c4bef38921db 100644
> > --- a/drivers/gpu/drm/drm_print.c
> > +++ b/drivers/gpu/drm/drm_print.c
> > @@ -31,6 +31,7 @@
> >  #include <linux/moduleparam.h>
> >  #include <linux/seq_file.h>
> >  #include <linux/slab.h>
> > +#include <linux/trace.h>
> >
> >  #include <drm/drm.h>
> >  #include <drm/drm_drv.h>
> > @@ -43,17 +44,34 @@
> >  unsigned int __drm_debug_syslog;
> >  EXPORT_SYMBOL(__drm_debug_syslog);
> >
> > -MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n"
> > -"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n"
> > -"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n"
> > -"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n"
> > -"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n"
> > -"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n"
> > -"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
> > -"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
> > -"\t\tBit 8 (0x100) will enable DP messages (displayport code)");
> > +/*
> > + * __drm_debug_trace: Enable debug output in drm tracing instance.
> > + * Bitmask of DRM_UT_x. See include/drm/drm_print.h for details.
> > + */
> > +unsigned int __drm_debug_trace;
> > +EXPORT_SYMBOL(__drm_debug_trace);
>
> Hi!

Hi Pekka,
Thanks again for the feedback, I'm happy that we seem to be converging!

>
> Might distributions perhaps want to set a default value for this via
> Kconfig? Or could setting it via sysfs happen early enough to diagnose
> e.g. Plymouth problems?
>
> Or maybe there is nothing to see from early boot?
>
> The general usefulness of this feature depends on whether people
> actually run with it enabled.

I had assumed that the cmdline argument would be sufficient for
distros, is Kconfig preferable here? The module parameter has the
advantage of being runtime configurable and is more in line with
drm.debug. We can do either in CrOS, so I'm happy to go with crowd
consensus.

Sean

>
> > +
> > +#define DEBUG_PARM_DESC(dst) \
> > +"Enable debug output to " dst ", where each bit enables a debug category.\n" \
> > +"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n" \
> > +"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n" \
> > +"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n" \
> > +"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n" \
> > +"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n" \
> > +"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n" \
> > +"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n" \
> > +"\t\tBit 8 (0x100) will enable DP messages (displayport code)"
> > +
> > +MODULE_PARM_DESC(debug, DEBUG_PARM_DESC("syslog"));
> >  module_param_named(debug, __drm_debug_syslog, int, 0600);
> >
> > +MODULE_PARM_DESC(trace, DEBUG_PARM_DESC("tracefs"));
> > +module_param_named(trace, __drm_debug_trace, int, 0600);
>
> ...
>
> > +
> > +/**
> > + * DOC: DRM Tracing
> > + *
> > + * *tl;dr* DRM tracing is a lightweight alternative to traditional DRM debug
> > + * logging.
> > + *
> > + * While DRM logging is quite convenient when reproducing a specific issue, it
> > + * doesn't help when something goes wrong unexpectedly. There are a couple
> > + * reasons why one does not want to enable DRM logging at all times:
> > + *
> > + * 1. We don't want to overwhelm syslog with drm spam, others have to use it too
> > + * 2. Console logging is slow
> > + *
> > + * DRM tracing aims to solve both these problems.
> > + *
> > + * To use DRM tracing, set the drm.trace module parameter (via cmdline or sysfs)
> > + * to a DRM debug category mask (this is a bitmask of &drm_debug_category
> > + * values):
> > + * ::
> > + *
> > + *    eg: echo 0x106 > /sys/module/drm/parameters/trace
> > + *
> > + * Once active, all log messages in the specified categories will be written to
> > + * the DRM trace. Once at capacity, the trace will overwrite old messages with
> > + * new ones. At any point, one can read the trace file to extract the previous N
> > + * DRM messages:
> > + * ::
> > + *
> > + *    eg: cat /sys/kernel/tracing/instances/drm/trace
> > + *
> > + * Considerations
> > + * **************
> > + * The trace is subsystem wide, so if you have multiple devices active, they
> > + * will be adding logs to the same trace.
> > + *
> > + * The contents of the DRM Trace are **not** considered UABI. **DO NOT depend on
> > + * the values of these traces in your userspace.** These traces are intended for
> > + * entertainment purposes only. The contents of these logs carry no warranty,
> > + * expressed or implied.
> > + */
>
> Sounds good to me!
> This part is:
> Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
>
>
> Thanks,
> pq
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Re: [PATCH v5 13/13] drm/print: Add tracefs support to the drm logging helpers

[Pekka Paalanen]

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On Wed, 10 Jun 2020 09:29:37 -0400
Sean Paul <sean@poorly.run> wrote:

> On Wed, Jun 10, 2020 at 3:57 AM Pekka Paalanen <ppaalanen@gmail.com> wrote:
> >
> > On Mon,  8 Jun 2020 17:05:03 -0400
> > Sean Paul <sean@poorly.run> wrote:
> >  
> > > From: Sean Paul <seanpaul@chromium.org>
> > >
> > > This patch adds a new module parameter called drm.trace which accepts
> > > the same mask as drm.debug. When a debug category is enabled, log
> > > messages will be put in a new tracefs instance called drm for
> > > consumption.
> > >
> > > Using the new tracefs instance will allow distros to enable drm logging
> > > in production without impacting performance or spamming the system
> > > logs.
> > >
> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > Cc: David Airlie <airlied@gmail.com>
> > > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > > Cc: Pekka Paalanen <ppaalanen@gmail.com>
> > > Cc: Rob Clark <robdclark@gmail.com>
> > > Cc: Steven Rostedt <rostedt@goodmis.org>
> > > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Steven Rostedt <rostedt@goodmis.org>
> > > Signed-off-by: Sean Paul <seanpaul@chromium.org>
> > > Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
> > > Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
> > > Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3
> > > Link: https://patchwork.freedesktop.org/patch/msgid/20200114172155.215463-1-sean@poorly.run #v4
> > >
> > > Changes in v5:
> > > -Re-write to use trace_array and the tracefs instance support
> > > ---
> > >  Documentation/gpu/drm-uapi.rst |   6 +
> > >  drivers/gpu/drm/drm_drv.c      |   3 +
> > >  drivers/gpu/drm/drm_print.c    | 209 ++++++++++++++++++++++++++++-----
> > >  include/drm/drm_print.h        |  63 ++++++++--
> > >  4 files changed, 241 insertions(+), 40 deletions(-)
> > >

...

> > >  #include <drm/drm.h>
> > >  #include <drm/drm_drv.h>
> > > @@ -43,17 +44,34 @@
> > >  unsigned int __drm_debug_syslog;
> > >  EXPORT_SYMBOL(__drm_debug_syslog);
> > >
> > > -MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n"
> > > -"\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n"
> > > -"\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n"
> > > -"\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n"
> > > -"\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n"
> > > -"\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n"
> > > -"\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
> > > -"\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
> > > -"\t\tBit 8 (0x100) will enable DP messages (displayport code)");
> > > +/*
> > > + * __drm_debug_trace: Enable debug output in drm tracing instance.
> > > + * Bitmask of DRM_UT_x. See include/drm/drm_print.h for details.
> > > + */
> > > +unsigned int __drm_debug_trace;
> > > +EXPORT_SYMBOL(__drm_debug_trace);  
> >
> > Hi!  
> 
> Hi Pekka,
> Thanks again for the feedback, I'm happy that we seem to be converging!
> 
> >
> > Might distributions perhaps want to set a default value for this via
> > Kconfig? Or could setting it via sysfs happen early enough to diagnose
> > e.g. Plymouth problems?
> >
> > Or maybe there is nothing to see from early boot?
> >
> > The general usefulness of this feature depends on whether people
> > actually run with it enabled.  
> 
> I had assumed that the cmdline argument would be sufficient for
> distros, is Kconfig preferable here? The module parameter has the
> advantage of being runtime configurable and is more in line with
> drm.debug. We can do either in CrOS, so I'm happy to go with crowd
> consensus.

Hi,

I don't know. I did mean only *default* value for the module parameter
via Kconfig. Right now your default value is implicit 0.

But that's just me thinking that making kernel command lines even
longer would be somehow bad. Maybe it's fine?


Thanks,
pq

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Re: [PATCH v5 00/13] drm/trace: Mirror DRM debug logs to tracefs

[Sean Paul]

On Mon, Jun 8, 2020 at 5:05 PM Sean Paul <sean@poorly.run> wrote:
>
> From: Sean Paul <seanpaul@chromium.org>
>
> This series is the latest in my journey to create a lightweight,
> always-on "flight recorder" (name credit Weston) of drm logs. This
> incarnation uses a trace_array to keep logs in memory exposed through
> tracefs. Users and distros can enable drm logs by using the drm.trace
> module parameter to choose the debug categories they are interested in.
>
> The set has ballooned a little bit since the last version. Reason being
> is that I decided to return true from drm_debug_enabled if trace was
> enabled. This should make it easier and more seamless for driver
> developers to use the correct interface, but meant I needed to audit all
> uses of drm_debug_enabled and drm_debug_printer.
>
> Out of all those calls, there are 3 situations which arose:
> 1- The logs should only go to syslog:
>         I've converted these to use the drm_debug_syslog variant of
>         enable check/printer.
>
> 2- The logs should go to both syslog/trace, but were using pr_debug():
>         I've converted these to use the proper drm logging helper. In
>         cases which used a drm_printer I've had to use a new
>         drm_debug_category_printer to ensure they are routed correctly.
>
> 3- The logs should go to both syslog/trace and are using drm logging fns:
>         These are untouched and should be routed to the appropriate
>         place(s)
>

Friendly ping. Is this something upstream wants, or should we continue
carrying it downstream?

Sean

>
> Sean Paul (13):
>   drm/mipi_dbi: Convert pr_debug calls to DRM_DEBUG_DRIVER
>   drm/sil164: Convert dev_printk to drm_dev_dbg
>   drm/i915/utils: Replace dev_printk with drm helpers
>   drm/msm/dpu: Replace definitions for dpu debug macros
>   drm/print: rename drm_debug* to be more syslog-centric
>   drm/amd: Gate i2c transaction logs on drm_debug_syslog
>   drm/etnaviv: Change buffer dump checks to target syslog
>   drm/nouveau: Change debug checks to specifically target syslog
>   drm/i915: Change infoframe debug checks to specify syslog
>   drm/print: Add drm_debug_category_printer
>   drm/mst: Convert debug printers to debug category printers
>   drm/i915: Use debug category printer for welcome message
>   drm/print: Add tracefs support to the drm logging helpers
>
>  Documentation/gpu/drm-uapi.rst               |   6 +
>  drivers/gpu/drm/amd/amdgpu/smu_v11_0_i2c.c   |   4 +-
>  drivers/gpu/drm/drm_dp_mst_topology.c        |   9 +-
>  drivers/gpu/drm/drm_drv.c                    |   3 +
>  drivers/gpu/drm/drm_mipi_dbi.c               |   8 +-
>  drivers/gpu/drm/drm_print.c                  | 228 ++++++++++++++++---
>  drivers/gpu/drm/etnaviv/etnaviv_buffer.c     |   8 +-
>  drivers/gpu/drm/i2c/sil164_drv.c             |  12 +-
>  drivers/gpu/drm/i915/display/intel_display.c |   4 +-
>  drivers/gpu/drm/i915/i915_drv.c              |   3 +-
>  drivers/gpu/drm/i915/i915_utils.c            |   5 +-
>  drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h      |  20 +-
>  drivers/gpu/drm/nouveau/dispnv50/disp.h      |   4 +-
>  drivers/gpu/drm/nouveau/nouveau_drv.h        |   4 +-
>  include/drm/drm_print.h                      |  96 +++++++-
>  15 files changed, 318 insertions(+), 96 deletions(-)
>
> --
> Sean Paul, Software Engineer, Google / Chromium OS
>
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