[PATCH v2 0/2] spi: axi-spi-engine: performance improvements

[PATCH v2 0/2] spi: axi-spi-engine: performance improvements

[David Lechner]

While researching potential performance improvements in the core SPI
code, we found a few low-hanging opportunities for improvements in the
AXI SPI engine driver.

---
Changes in v2:
- Remove include of linux/idr.h header.
- Picked up Nuno's review tags.
- Link to v1: https://lore.kernel.org/r/20240206-axi-spi-engine-round-2-1-v1-0-ea6eeb60f4fb@baylibre.com

---
David Lechner (2):
      spi: axi-spi-engine: remove use of ida for sync id
      spi: axi-spi-engine: move msg finalization out of irq handler

 drivers/spi/spi-axi-spi-engine.c | 68 +++++++++++++---------------------------
 1 file changed, 21 insertions(+), 47 deletions(-)
---
base-commit: 80fa6a033ac8c395a3de4840e204638e92b8b371
change-id: 20240206-axi-spi-engine-round-2-1-bb73990abac3

[PATCH v2 1/2] spi: axi-spi-engine: remove use of ida for sync id

[David Lechner]

Profiling has shown that ida_alloc_range() accounts for about 10% of the
time spent in spi_sync() when using the AXI SPI Engine controller. This
call is used to create a unique id for each SPI message to match to an
IRQ when the message is complete.

Since the core SPI code serializes messages in a message queue, we can
only have one message in flight at a time, namely host->cur_msg. This
means that we can use a fixed value instead of a unique id for each
message since there can never be more than one message pending at a
time.

This patch removes the use of ida for the sync id and replaces it with a
constant value. This simplifies the driver and improves performance.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
---
 drivers/spi/spi-axi-spi-engine.c | 28 ++++++----------------------
 1 file changed, 6 insertions(+), 22 deletions(-)

diff --git a/drivers/spi/spi-axi-spi-engine.c b/drivers/spi/spi-axi-spi-engine.c
index 6b0c72bf3395..606389566129 100644
--- a/drivers/spi/spi-axi-spi-engine.c
+++ b/drivers/spi/spi-axi-spi-engine.c
@@ -7,7 +7,6 @@
 
 #include <linux/clk.h>
 #include <linux/fpga/adi-axi-common.h>
-#include <linux/idr.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/of.h>
@@ -57,6 +56,9 @@
 #define SPI_ENGINE_TRANSFER_WRITE		0x1
 #define SPI_ENGINE_TRANSFER_READ		0x2
 
+/* Arbitrary sync ID for use by host->cur_msg */
+#define AXI_SPI_ENGINE_CUR_MSG_SYNC_ID		0x1
+
 #define SPI_ENGINE_CMD(inst, arg1, arg2) \
 	(((inst) << 12) | ((arg1) << 8) | (arg2))
 
@@ -98,8 +100,6 @@ struct spi_engine_message_state {
 	unsigned int rx_length;
 	/** @rx_buf: Bytes not yet written to the RX FIFO. */
 	uint8_t *rx_buf;
-	/** @sync_id: ID to correlate SYNC interrupts with this message. */
-	u8 sync_id;
 };
 
 struct spi_engine {
@@ -109,7 +109,6 @@ struct spi_engine {
 	spinlock_t lock;
 
 	void __iomem *base;
-	struct ida sync_ida;
 	struct timer_list watchdog_timer;
 	struct spi_controller *controller;
 
@@ -483,9 +482,7 @@ static irqreturn_t spi_engine_irq(int irq, void *devid)
 	}
 
 	if (pending & SPI_ENGINE_INT_SYNC && msg) {
-		struct spi_engine_message_state *st = msg->state;
-
-		if (completed_id == st->sync_id) {
+		if (completed_id == AXI_SPI_ENGINE_CUR_MSG_SYNC_ID) {
 			if (timer_delete_sync(&spi_engine->watchdog_timer)) {
 				msg->status = 0;
 				msg->actual_length = msg->frame_length;
@@ -510,10 +507,8 @@ static int spi_engine_prepare_message(struct spi_controller *host,
 				      struct spi_message *msg)
 {
 	struct spi_engine_program p_dry, *p;
-	struct spi_engine *spi_engine = spi_controller_get_devdata(host);
 	struct spi_engine_message_state *st;
 	size_t size;
-	int ret;
 
 	st = kzalloc(sizeof(*st), GFP_KERNEL);
 	if (!st)
@@ -531,18 +526,10 @@ static int spi_engine_prepare_message(struct spi_controller *host,
 		return -ENOMEM;
 	}
 
-	ret = ida_alloc_range(&spi_engine->sync_ida, 0, U8_MAX, GFP_KERNEL);
-	if (ret < 0) {
-		kfree(p);
-		kfree(st);
-		return ret;
-	}
-
-	st->sync_id = ret;
-
 	spi_engine_compile_message(msg, false, p);
 
-	spi_engine_program_add_cmd(p, false, SPI_ENGINE_CMD_SYNC(st->sync_id));
+	spi_engine_program_add_cmd(p, false, SPI_ENGINE_CMD_SYNC(
+						AXI_SPI_ENGINE_CUR_MSG_SYNC_ID));
 
 	st->p = p;
 	st->cmd_buf = p->instructions;
@@ -555,10 +542,8 @@ static int spi_engine_prepare_message(struct spi_controller *host,
 static int spi_engine_unprepare_message(struct spi_controller *host,
 					struct spi_message *msg)
 {
-	struct spi_engine *spi_engine = spi_controller_get_devdata(host);
 	struct spi_engine_message_state *st = msg->state;
 
-	ida_free(&spi_engine->sync_ida, st->sync_id);
 	kfree(st->p);
 	kfree(st);
 
@@ -640,7 +625,6 @@ static int spi_engine_probe(struct platform_device *pdev)
 	spi_engine = spi_controller_get_devdata(host);
 
 	spin_lock_init(&spi_engine->lock);
-	ida_init(&spi_engine->sync_ida);
 	timer_setup(&spi_engine->watchdog_timer, spi_engine_timeout, TIMER_IRQSAFE);
 	spi_engine->controller = host;
 

-- 
2.43.0

[PATCH v2 2/2] spi: axi-spi-engine: move msg finalization out of irq handler

[David Lechner]

As a general principal, it is best to do as little as possible in an
interrupt handler. This patch reworks the AXI SPI Engine driver to move
timer_delete_sync() and spi_finalize_current_message() out of the
interrupt handler. Instead, spi_finalize_current_message() is moved to
the transfer_one_message function (similar to nearly all other SPI
controllers). A completion is now used to wait for the sync interrupt
that indicates that the message is complete. The watchdog timer is no
longer needed since we can use the wait_for_completion_timeout()
function to wait for the message to complete with the same effect.

As a bonus, these changes also improve throughput of the SPI controller.
For example, this was tested on a ZynqMP with a 80MHz SCLK reading 4
byte samples from an ADC. The max measured throughput increased from
26k to 28k samples per second.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
---
 drivers/spi/spi-axi-spi-engine.c | 40 +++++++++++++++-------------------------
 1 file changed, 15 insertions(+), 25 deletions(-)

diff --git a/drivers/spi/spi-axi-spi-engine.c b/drivers/spi/spi-axi-spi-engine.c
index 606389566129..ca66d202f0e2 100644
--- a/drivers/spi/spi-axi-spi-engine.c
+++ b/drivers/spi/spi-axi-spi-engine.c
@@ -6,6 +6,7 @@
  */
 
 #include <linux/clk.h>
+#include <linux/completion.h>
 #include <linux/fpga/adi-axi-common.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
@@ -13,7 +14,6 @@
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/spi/spi.h>
-#include <linux/timer.h>
 
 #define SPI_ENGINE_REG_RESET			0x40
 
@@ -109,9 +109,7 @@ struct spi_engine {
 	spinlock_t lock;
 
 	void __iomem *base;
-	struct timer_list watchdog_timer;
-	struct spi_controller *controller;
-
+	struct completion msg_complete;
 	unsigned int int_enable;
 };
 
@@ -483,11 +481,9 @@ static irqreturn_t spi_engine_irq(int irq, void *devid)
 
 	if (pending & SPI_ENGINE_INT_SYNC && msg) {
 		if (completed_id == AXI_SPI_ENGINE_CUR_MSG_SYNC_ID) {
-			if (timer_delete_sync(&spi_engine->watchdog_timer)) {
-				msg->status = 0;
-				msg->actual_length = msg->frame_length;
-				spi_finalize_current_message(host);
-			}
+			msg->status = 0;
+			msg->actual_length = msg->frame_length;
+			complete(&spi_engine->msg_complete);
 			disable_int |= SPI_ENGINE_INT_SYNC;
 		}
 	}
@@ -558,7 +554,7 @@ static int spi_engine_transfer_one_message(struct spi_controller *host,
 	unsigned int int_enable = 0;
 	unsigned long flags;
 
-	mod_timer(&spi_engine->watchdog_timer, jiffies + msecs_to_jiffies(5000));
+	reinit_completion(&spi_engine->msg_complete);
 
 	spin_lock_irqsave(&spi_engine->lock, flags);
 
@@ -580,21 +576,16 @@ static int spi_engine_transfer_one_message(struct spi_controller *host,
 	spi_engine->int_enable = int_enable;
 	spin_unlock_irqrestore(&spi_engine->lock, flags);
 
-	return 0;
-}
-
-static void spi_engine_timeout(struct timer_list *timer)
-{
-	struct spi_engine *spi_engine = from_timer(spi_engine, timer, watchdog_timer);
-	struct spi_controller *host = spi_engine->controller;
-
-	if (WARN_ON(!host->cur_msg))
-		return;
+	if (!wait_for_completion_timeout(&spi_engine->msg_complete,
+					 msecs_to_jiffies(5000))) {
+		dev_err(&host->dev,
+			"Timeout occurred while waiting for transfer to complete. Hardware is probably broken.\n");
+		msg->status = -ETIMEDOUT;
+	}
 
-	dev_err(&host->dev,
-		"Timeout occurred while waiting for transfer to complete. Hardware is probably broken.\n");
-	host->cur_msg->status = -ETIMEDOUT;
 	spi_finalize_current_message(host);
+
+	return msg->status;
 }
 
 static void spi_engine_release_hw(void *p)
@@ -625,8 +616,7 @@ static int spi_engine_probe(struct platform_device *pdev)
 	spi_engine = spi_controller_get_devdata(host);
 
 	spin_lock_init(&spi_engine->lock);
-	timer_setup(&spi_engine->watchdog_timer, spi_engine_timeout, TIMER_IRQSAFE);
-	spi_engine->controller = host;
+	init_completion(&spi_engine->msg_complete);
 
 	spi_engine->clk = devm_clk_get_enabled(&pdev->dev, "s_axi_aclk");
 	if (IS_ERR(spi_engine->clk))

-- 
2.43.0

Re: [PATCH v2 0/2] spi: axi-spi-engine: performance improvements

[Mark Brown]

On Wed, 07 Feb 2024 08:51:23 -0600, David Lechner wrote:
> While researching potential performance improvements in the core SPI
> code, we found a few low-hanging opportunities for improvements in the
> AXI SPI engine driver.
> 

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/2] spi: axi-spi-engine: remove use of ida for sync id
      commit: 531860e12da76a444e0ecfd37a9d786e7986957a
[2/2] spi: axi-spi-engine: move msg finalization out of irq handler
      commit: abb4b46c43689dd1f4d80c41e49127ca0ede75b3

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark