[PATCH 0/2] mmc: bcm2835_sdhost: use fallback clock rate

[PATCH 0/2] mmc: bcm2835_sdhost: use fallback clock rate

[Vincent Fazio]

Recent raspberry pi firmware has modified the behavior of GET_CLOCK_RATE
to return zero (0) when there is no previous call to SET_CLOCK_RATE.

This affects callers of bcm2835_get_mmc_clock and can lead to degraded
MMC performance.

Now, return the result of GET_MAX_CLOCK_RATE if GET_CLOCK_RATE is zero.

Additionally, let the firmware manage SDCDIV when possible.


Vincent Fazio (2):
  arm: rpi: fallback to max clock rate for MMC clock
  mmc: bcm2835-host: let firmware manage the clock divisor

 arch/arm/mach-bcm283x/include/mach/mbox.h | 18 ++++++++
 arch/arm/mach-bcm283x/include/mach/msg.h  | 10 +++++
 arch/arm/mach-bcm283x/msg.c               | 47 +++++++++++++++++++-
 drivers/mmc/bcm2835_sdhost.c              | 53 ++++++++++++++---------
 4 files changed, 106 insertions(+), 22 deletions(-)

-- 
2.25.1

[PATCH 1/2] arm: rpi: fallback to max clock rate for MMC clock

[Vincent Fazio]

In rpi-firmware 25e2b597ebfb2495eab4816a276758dcc6ea21f1,
the GET_CLOCK_RATE mailbox property was changed to return the last
value set by SET_CLOCK_RATE.

https://github.com/raspberrypi/firmware/issues/1619#issuecomment-917025502

Due to this change in firmware behavior, bcm2835_get_mmc_clock now
returns a clock rate of zero since we do not issue SET_CLOCK_RATE.
This results in degraded MMC performance.

SET_CLOCK_RATE fixes the clock to a specific value and disables scaling
so is not an ideal solution.

Instead, fallback to GET_MAX_CLOCK_RATE in bcm2835_get_mmc_clock if
GET_CLOCK_RATE returns zero.

Signed-off-by: Vincent Fazio <vfazio@xes-inc.com>
---
 arch/arm/mach-bcm283x/include/mach/mbox.h |  2 ++
 arch/arm/mach-bcm283x/msg.c               | 19 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-bcm283x/include/mach/mbox.h b/arch/arm/mach-bcm283x/include/mach/mbox.h
index 2ae2d3d97c..7dcac583cc 100644
--- a/arch/arm/mach-bcm283x/include/mach/mbox.h
+++ b/arch/arm/mach-bcm283x/include/mach/mbox.h
@@ -224,6 +224,8 @@ struct bcm2835_mbox_tag_set_power_state {
 };
 
 #define BCM2835_MBOX_TAG_GET_CLOCK_RATE	0x00030002
+#define BCM2835_MBOX_TAG_GET_MAX_CLOCK_RATE	0x00030004
+#define BCM2835_MBOX_TAG_GET_MIN_CLOCK_RATE	0x00030007
 
 #define BCM2835_MBOX_CLOCK_ID_EMMC	1
 #define BCM2835_MBOX_CLOCK_ID_UART	2
diff --git a/arch/arm/mach-bcm283x/msg.c b/arch/arm/mach-bcm283x/msg.c
index 347aece3cd..ae85e9159e 100644
--- a/arch/arm/mach-bcm283x/msg.c
+++ b/arch/arm/mach-bcm283x/msg.c
@@ -75,6 +75,7 @@ int bcm2835_get_mmc_clock(u32 clock_id)
 {
 	ALLOC_CACHE_ALIGN_BUFFER(struct msg_get_clock_rate, msg_clk, 1);
 	int ret;
+	u32 clock_rate = 0;
 
 	ret = bcm2835_power_on_module(BCM2835_MBOX_POWER_DEVID_SDHCI);
 	if (ret)
@@ -90,7 +91,23 @@ int bcm2835_get_mmc_clock(u32 clock_id)
 		return -EIO;
 	}
 
-	return msg_clk->get_clock_rate.body.resp.rate_hz;
+	clock_rate = msg_clk->get_clock_rate.body.resp.rate_hz;
+
+	if (clock_rate == 0) {
+		BCM2835_MBOX_INIT_HDR(msg_clk);
+		BCM2835_MBOX_INIT_TAG(&msg_clk->get_clock_rate, GET_MAX_CLOCK_RATE);
+		msg_clk->get_clock_rate.body.req.clock_id = clock_id;
+
+		ret = bcm2835_mbox_call_prop(BCM2835_MBOX_PROP_CHAN, &msg_clk->hdr);
+		if (ret) {
+			printf("bcm2835: Could not query max eMMC clock rate\n");
+			return -EIO;
+		}
+
+		clock_rate = msg_clk->get_clock_rate.body.resp.rate_hz;
+	}
+
+	return clock_rate;
 }
 
 int bcm2835_get_video_size(int *widthp, int *heightp)
-- 
2.25.1

[PATCH 2/2] mmc: bcm2835-host: let firmware manage the clock divisor

[Vincent Fazio]

Newer firmware can manage the SDCDIV clock divisor register, allowing
the divisor to scale with the core as necessary.

Leverage this ability if the firmware supports it.

Adapted from the following raspberrypi Linux kernel commit:

  bcm2835-sdhost: Firmware manages the clock divisor
  https://github.com/raspberrypi/linux/commit/08532d242d7702ae0add95096aa49c5e96e066e2

Signed-off-by: Vincent Fazio <vfazio@xes-inc.com>
---
 arch/arm/mach-bcm283x/include/mach/mbox.h | 16 +++++++
 arch/arm/mach-bcm283x/include/mach/msg.h  | 10 +++++
 arch/arm/mach-bcm283x/msg.c               | 28 ++++++++++++
 drivers/mmc/bcm2835_sdhost.c              | 53 ++++++++++++++---------
 4 files changed, 86 insertions(+), 21 deletions(-)

diff --git a/arch/arm/mach-bcm283x/include/mach/mbox.h b/arch/arm/mach-bcm283x/include/mach/mbox.h
index 7dcac583cc..490664f878 100644
--- a/arch/arm/mach-bcm283x/include/mach/mbox.h
+++ b/arch/arm/mach-bcm283x/include/mach/mbox.h
@@ -252,6 +252,22 @@ struct bcm2835_mbox_tag_get_clock_rate {
 	} body;
 };
 
+#define BCM2835_MBOX_TAG_SET_SDHOST_CLOCK	0x00038042
+
+struct bcm2835_mbox_tag_set_sdhost_clock {
+	struct bcm2835_mbox_tag_hdr tag_hdr;
+	union {
+		struct {
+			u32 rate_hz;
+		} req;
+		struct {
+			u32 rate_hz;
+			u32 rate_1;
+			u32 rate_2;
+		} resp;
+	} body;
+};
+
 #define BCM2835_MBOX_TAG_ALLOCATE_BUFFER	0x00040001
 
 struct bcm2835_mbox_tag_allocate_buffer {
diff --git a/arch/arm/mach-bcm283x/include/mach/msg.h b/arch/arm/mach-bcm283x/include/mach/msg.h
index e45c1bf010..ab37abdb6c 100644
--- a/arch/arm/mach-bcm283x/include/mach/msg.h
+++ b/arch/arm/mach-bcm283x/include/mach/msg.h
@@ -22,6 +22,16 @@ int bcm2835_power_on_module(u32 module);
  */
 int bcm2835_get_mmc_clock(u32 clock_id);
 
+/**
+ * bcm2835_set_sdhost_clock() - determine if firmware controls sdhost cdiv
+ *
+ * @rate_hz: Input clock frequency
+ * @rate_1: Returns a clock frequency
+ * @rate_2: Returns a clock frequency
+ * @return 0 of OK, -EIO on error
+ */
+int bcm2835_set_sdhost_clock(u32 rate_hz, u32 *rate_1, u32 *rate_2);
+
 /**
  * bcm2835_get_video_size() - get the current display size
  *
diff --git a/arch/arm/mach-bcm283x/msg.c b/arch/arm/mach-bcm283x/msg.c
index ae85e9159e..adab15da4e 100644
--- a/arch/arm/mach-bcm283x/msg.c
+++ b/arch/arm/mach-bcm283x/msg.c
@@ -21,6 +21,12 @@ struct msg_get_clock_rate {
 	u32 end_tag;
 };
 
+struct msg_set_sdhost_clock {
+	struct bcm2835_mbox_hdr hdr;
+	struct bcm2835_mbox_tag_set_sdhost_clock set_sdhost_clock;
+	u32 end_tag;
+};
+
 struct msg_query {
 	struct bcm2835_mbox_hdr hdr;
 	struct bcm2835_mbox_tag_physical_w_h physical_w_h;
@@ -110,6 +116,28 @@ int bcm2835_get_mmc_clock(u32 clock_id)
 	return clock_rate;
 }
 
+int bcm2835_set_sdhost_clock(u32 rate_hz, u32 *rate_1, u32 *rate_2)
+{
+	ALLOC_CACHE_ALIGN_BUFFER(struct msg_set_sdhost_clock, msg_sdhost_clk, 1);
+	int ret;
+
+	BCM2835_MBOX_INIT_HDR(msg_sdhost_clk);
+	BCM2835_MBOX_INIT_TAG(&msg_sdhost_clk->set_sdhost_clock, SET_SDHOST_CLOCK);
+
+	msg_sdhost_clk->set_sdhost_clock.body.req.rate_hz = rate_hz;
+
+	ret = bcm2835_mbox_call_prop(BCM2835_MBOX_PROP_CHAN, &msg_sdhost_clk->hdr);
+	if (ret) {
+		printf("bcm2835: Could not query sdhost clock rate\n");
+		return -EIO;
+	}
+
+	*rate_1 = msg_sdhost_clk->set_sdhost_clock.body.resp.rate_1;
+	*rate_2 = msg_sdhost_clk->set_sdhost_clock.body.resp.rate_2;
+
+	return 0;
+}
+
 int bcm2835_get_video_size(int *widthp, int *heightp)
 {
 	ALLOC_CACHE_ALIGN_BUFFER(struct msg_query, msg_query, 1);
diff --git a/drivers/mmc/bcm2835_sdhost.c b/drivers/mmc/bcm2835_sdhost.c
index 894dbdd686..5c23c03d10 100644
--- a/drivers/mmc/bcm2835_sdhost.c
+++ b/drivers/mmc/bcm2835_sdhost.c
@@ -181,6 +181,7 @@ struct bcm2835_host {
 	struct udevice		*dev;
 	struct mmc		*mmc;
 	struct bcm2835_plat	*plat;
+	unsigned int		firmware_sets_cdiv:1;
 };
 
 static void bcm2835_dumpregs(struct bcm2835_host *host)
@@ -233,7 +234,7 @@ static void bcm2835_reset_internal(struct bcm2835_host *host)
 	msleep(20);
 	host->clock = 0;
 	writel(host->hcfg, host->ioaddr + SDHCFG);
-	writel(host->cdiv, host->ioaddr + SDCDIV);
+	writel(SDCDIV_MAX_CDIV, host->ioaddr + SDCDIV);
 }
 
 static int bcm2835_wait_transfer_complete(struct bcm2835_host *host)
@@ -598,6 +599,7 @@ static int bcm2835_transmit(struct bcm2835_host *host)
 static void bcm2835_set_clock(struct bcm2835_host *host, unsigned int clock)
 {
 	int div;
+	u32 clock_rate[2] = { 0 };
 
 	/* The SDCDIV register has 11 bits, and holds (div - 2).  But
 	 * in data mode the max is 50MHz wihout a minimum, and only
@@ -620,26 +622,34 @@ static void bcm2835_set_clock(struct bcm2835_host *host, unsigned int clock)
 	 * clock divisor at all times.
 	 */
 
-	if (clock < 100000) {
-		/* Can't stop the clock, but make it as slow as possible
-		 * to show willing
-		 */
-		host->cdiv = SDCDIV_MAX_CDIV;
-		writel(host->cdiv, host->ioaddr + SDCDIV);
-		return;
-	}
+	if (host->firmware_sets_cdiv) {
+		bcm2835_set_sdhost_clock(clock, &clock_rate[0], &clock_rate[1]);
+		clock = max(clock_rate[0], clock_rate[1]);
+	} else {
+		if (clock < 100000) {
+			/* Can't stop the clock, but make it as slow as possible
+			* to show willing
+			*/
+			host->cdiv = SDCDIV_MAX_CDIV;
+			writel(host->cdiv, host->ioaddr + SDCDIV);
+			return;
+		}
 
-	div = host->max_clk / clock;
-	if (div < 2)
-		div = 2;
-	if ((host->max_clk / div) > clock)
-		div++;
-	div -= 2;
+		div = host->max_clk / clock;
+		if (div < 2)
+			div = 2;
+		if ((host->max_clk / div) > clock)
+			div++;
+		div -= 2;
 
-	if (div > SDCDIV_MAX_CDIV)
-		div = SDCDIV_MAX_CDIV;
+		if (div > SDCDIV_MAX_CDIV)
+			div = SDCDIV_MAX_CDIV;
+
+		clock = host->max_clk / (div + 2);
+		host->cdiv = div;
+		writel(host->cdiv, host->ioaddr + SDCDIV);
+	}
 
-	clock = host->max_clk / (div + 2);
 	host->mmc->clock = clock;
 
 	/* Calibrate some delays */
@@ -647,9 +657,6 @@ static void bcm2835_set_clock(struct bcm2835_host *host, unsigned int clock)
 	host->ns_per_fifo_word = (1000000000 / clock) *
 		((host->mmc->card_caps & MMC_MODE_4BIT) ? 8 : 32);
 
-	host->cdiv = div;
-	writel(host->cdiv, host->ioaddr + SDCDIV);
-
 	/* Set the timeout to 500ms */
 	writel(host->mmc->clock / 2, host->ioaddr + SDTOUT);
 }
@@ -759,6 +766,7 @@ static int bcm2835_probe(struct udevice *dev)
 	struct bcm2835_host *host = dev_get_priv(dev);
 	struct mmc *mmc = mmc_get_mmc_dev(dev);
 	struct mmc_uclass_priv *upriv = dev_get_uclass_priv(dev);
+	u32 clock_rate[2] = { ~0 };
 
 	host->dev = dev;
 	host->mmc = mmc;
@@ -776,6 +784,9 @@ static int bcm2835_probe(struct udevice *dev)
 
 	host->max_clk = bcm2835_get_mmc_clock(BCM2835_MBOX_CLOCK_ID_CORE);
 
+	bcm2835_set_sdhost_clock(0, &clock_rate[0], &clock_rate[1]);
+	host->firmware_sets_cdiv = (clock_rate[0] != ~0);
+
 	bcm2835_add_host(host);
 
 	dev_dbg(dev, "%s -> OK\n", __func__);
-- 
2.25.1