[PATCH v3] mmc: core: Set HS clock speed before sending HS CMD13

[Brian Norris <briannorris@chromium.org>]

Way back in commit 4f25580fb84d ("mmc: core: changes frequency to
hs_max_dtr when selecting hs400es"), Rockchip engineers noticed that
some eMMC don't respond to SEND_STATUS commands very reliably if they're
still running at a low initial frequency. As mentioned in that commit,
JESD84-B51 P49 suggests a sequence in which the host:
1. sets HS_TIMING
2. bumps the clock ("<= 52 MHz")
3. sends further commands

It doesn't exactly require that we don't use a lower-than-52MHz
frequency, but in practice, these eMMC don't like it.

The aforementioned commit tried to get that right for HS400ES, although
it's unclear whether this ever truly worked as committed into mainline,
as other changes/refactoring adjusted the sequence in conflicting ways:

08573eaf1a70 ("mmc: mmc: do not use CMD13 to get status after speed mode
switch")

53e60650f74e ("mmc: core: Allow CMD13 polling when switching to HS mode
for mmc")

In any case, today we do step 3 before step 2. Let's fix that, and also
apply the same logic to HS200/400, where this eMMC has problems too.

Resolves errors like this seen when booting some RK3399 Gru/Scarlet
systems:

[    2.058881] mmc1: CQHCI version 5.10
[    2.097545] mmc1: SDHCI controller on fe330000.mmc [fe330000.mmc] using ADMA
[    2.209804] mmc1: mmc_select_hs400es failed, error -84
[    2.215597] mmc1: error -84 whilst initialising MMC card
[    2.417514] mmc1: mmc_select_hs400es failed, error -110
[    2.423373] mmc1: error -110 whilst initialising MMC card
[    2.605052] mmc1: mmc_select_hs400es failed, error -110
[    2.617944] mmc1: error -110 whilst initialising MMC card
[    2.835884] mmc1: mmc_select_hs400es failed, error -110
[    2.841751] mmc1: error -110 whilst initialising MMC card

Fixes: 08573eaf1a70 ("mmc: mmc: do not use CMD13 to get status after speed mode switch")
Fixes: 53e60650f74e ("mmc: core: Allow CMD13 polling when switching to HS mode for mmc")
Fixes: 4f25580fb84d ("mmc: core: changes frequency to hs_max_dtr when selecting hs400es")
Cc: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
---

Changes in v3:
 * Use mmc_set_bus_speed() to help choose the right clock rate
 * Avoid redundant clock rate changes
 * Restore clock rate on failed HS200 switch

Changes in v2:
 * Use ext_csd.hs200_max_dtr for HS200
 * Retest on top of 3b6c472822f8 ("mmc: core: Improve fallback to speed
   modes if eMMC HS200 fails")

 drivers/mmc/core/core.c |  3 +++
 drivers/mmc/core/mmc.c  | 21 +++++++++++++++++----
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 368f10405e13..61abae221623 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -914,6 +914,9 @@ void mmc_set_clock(struct mmc_host *host, unsigned int hz)
 	if (hz > host->f_max)
 		hz = host->f_max;
 
+	if (host->ios.clock == hz)
+		return;
+
 	host->ios.clock = hz;
 	mmc_set_ios(host);
 }
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index e7ea45386c22..1f22f1d2e9b8 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1384,13 +1384,17 @@ static int mmc_select_hs400es(struct mmc_card *card)
 		goto out_err;
 	}
 
+	/*
+	 * Bump to HS timing and frequency. Some cards don't handle
+	 * SEND_STATUS reliably at the initial frequency.
+	 */
 	mmc_set_timing(host, MMC_TIMING_MMC_HS);
+	mmc_set_bus_speed(card);
+
 	err = mmc_switch_status(card, true);
 	if (err)
 		goto out_err;
 
-	mmc_set_clock(host, card->ext_csd.hs_max_dtr);
-
 	/* Switch card to DDR with strobe bit */
 	val = EXT_CSD_DDR_BUS_WIDTH_8 | EXT_CSD_BUS_WIDTH_STROBE;
 	err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
@@ -1448,7 +1452,7 @@ static int mmc_select_hs400es(struct mmc_card *card)
 static int mmc_select_hs200(struct mmc_card *card)
 {
 	struct mmc_host *host = card->host;
-	unsigned int old_timing, old_signal_voltage;
+	unsigned int old_timing, old_signal_voltage, old_clock;
 	int err = -EINVAL;
 	u8 val;
 
@@ -1479,8 +1483,15 @@ static int mmc_select_hs200(struct mmc_card *card)
 				   false, true, MMC_CMD_RETRIES);
 		if (err)
 			goto err;
+
+		/*
+		 * Bump to HS200 timing and frequency. Some cards don't
+		 * handle SEND_STATUS reliably at the initial frequency.
+		 */
 		old_timing = host->ios.timing;
+		old_clock = host->ios.clock;
 		mmc_set_timing(host, MMC_TIMING_MMC_HS200);
+		mmc_set_bus_speed(card);
 
 		/*
 		 * For HS200, CRC errors are not a reliable way to know the
@@ -1493,8 +1504,10 @@ static int mmc_select_hs200(struct mmc_card *card)
 		 * mmc_select_timing() assumes timing has not changed if
 		 * it is a switch error.
 		 */
-		if (err == -EBADMSG)
+		if (err == -EBADMSG) {
+			mmc_set_clock(host, old_clock);
 			mmc_set_timing(host, old_timing);
+		}
 	}
 err:
 	if (err) {
-- 
2.35.1.1094.g7c7d902a7c-goog