linux-kernel - [PATCH v2] mmc: core: Don't set HS200 clock rate prematurely

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Message-Id: <20220422002318.3587413-1-briannorris@chromium.org>
Date:   Thu, 21 Apr 2022 17:23:18 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Shawn Lin <shawn.lin@...k-chips.com>, linux-mmc@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Luca Weiss <luca@...tu.xyz>, linux-kernel@...r.kernel.org,
        Heiner Kallweit <hkallweit1@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Brian Norris <briannorris@...omium.org>
Subject: [PATCH v2] mmc: core: Don't set HS200 clock rate prematurely

Commit 1c7ec586fe55 ("mmc: core: Set HS clock speed before sending HS
CMD13") fixes problems with certain eMMC, but introduced new ones with
others:

  qcom-msm8974-fairphone-fp2:

  [    1.868608] mmc0: SDHCI controller on f9824900.sdhci [f9824900.sdhci] using ADMA 64-bit
  [    1.925220] mmc0: mmc_select_hs200 failed, error -110
  [    1.925285] mmc0: error -110 whilst initialising MMC card

It appears we've overshot the acceptable clock rate here; while JESD84
suggests that we can bump to 52 MHz before switching (CMD6) to HS400, it
does *not* say we can switch to 200 MHz before switching to HS200 (see
page 45 / table 28). Use the HS bounds (typically 52 MHz) instead of the
HS200 bounds (which are only applicable after we successfully switch).

Link: https://lore.kernel.org/lkml/11962455.O9o76ZdvQC@g550jk/
Fixes: 1c7ec586fe55 ("mmc: core: Set HS clock speed before sending HS CMD13")
Reported-by: Luca Weiss <luca@...tu.xyz>
Signed-off-by: Brian Norris <briannorris@...omium.org>
---
Apologies for the quick resend; I fumbled the commit/send, even though I
had already updated the comments...

Changes in v2:
 * Updated comments

 drivers/mmc/core/mmc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 9ab915b5737a..82ca62c8669c 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1485,13 +1485,15 @@ static int mmc_select_hs200(struct mmc_card *card)
 			goto err;
 
 		/*
-		 * Bump to HS200 timing and frequency. Some cards don't
-		 * handle SEND_STATUS reliably at the initial frequency.
+		 * Bump to HS timing and frequency. Some cards don't handle
+		 * SEND_STATUS reliably at the initial frequency.
+		 * NB: We can't move to full (HS200) speeds until after we've
+		 * successfully switched over.
 		 */
 		old_timing = host->ios.timing;
 		old_clock = host->ios.clock;
 		mmc_set_timing(host, MMC_TIMING_MMC_HS200);
-		mmc_set_bus_speed(card);
+		mmc_set_clock(card->host, card->ext_csd.hs_max_dtr);
 
 		/*
 		 * For HS200, CRC errors are not a reliable way to know the
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog