linux-kernel - [PATCH] mmc: core: Remove timeout when enabling cache

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Date:   Tue,  6 Nov 2018 14:30:07 +0100
From:   Sjoerd Simons <sjoerd.simons@...labora.co.uk>
To:     linux-mmc@...r.kernel.org
Cc:     kernel@...labora.com, linux-kernel@...r.kernel.org,
        Hongjie Fang <hongjiefang@...micro.com>,
        Bastian Stender <bst@...gutronix.de>,
        Kyle Roeschley <kyle.roeschley@...com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Harish Jenny K N <harish_kandiga@...tor.com>,
        Simon Horman <horms+renesas@...ge.net.au>
Subject: [PATCH] mmc: core: Remove timeout when enabling cache

On some of our boards containing Micron eMMC chips compatible with
the eMMC 5.0 specification we starting seeing boot failures due to
timeouts:
  mmc1: error -110 whilst initialising MMC card

It turns out that switching the cache on after a power loss event can
take quite long. In some simple testing thusfar we've seen values up to
700ms, which is far longer then the GENERIC_CMD6_TIME of the chip
(250ms).

Looking at both the eMMC 4.51 and 5.0 specification there doesn't seem
to be a defined upper bound for the CACHE_CTRL ON command. For both
CACHE_CTRL OFF and FLUSH_CACHE it is documented that they can take
essentially unbounded time, but CACHE_CTRL ON i get the impression that
it's assumed to be "fast". Unfortunately this is not true in reality.

To resolve this, simply drop the timeout from CACHE_CTRL ON and assume
it might take an unbounded time similar to the FLUSH_CACHE command.

Signed-off-by: Sjoerd Simons <sjoerd.simons@...labora.co.uk>

---

 drivers/mmc/core/mmc.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index bc1bd2c25613..ac70b508a939 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1794,8 +1794,7 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 	if (!mmc_card_broken_hpi(card) &&
 	    card->ext_csd.cache_size > 0) {
 		err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
-				EXT_CSD_CACHE_CTRL, 1,
-				card->ext_csd.generic_cmd6_time);
+				EXT_CSD_CACHE_CTRL, 1, 0);
 		if (err && err != -EBADMSG)
 			goto free_card;

-- 
2.19.1