[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 at 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