[PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher

On 2 June 2016 at 11:35, Krzysztof Kozlowski [off-list ref] wrote:

On Thu, Jun 2, 2016 at 10:31 AM, Ulf Hansson [off-list ref] wrote:

quoted

+ Linus

On 29 May 2016 at 09:04, Chen-Yu Tsai [off-list ref] wrote:

quoted

When IS_ERR_VALUE was removed from the mmc core code, it was replaced
with a simple not-zero check. This does not work, as the value checked
is the return value for mmc_select_bus_width, which returns the set
bit width on success. This made eMMC modes higher than HS-DDR unusable.

Fix this by checking for a positive return value instead.

Fixes: 287980e49ffc ("remove lots of IS_ERR_VALUE abuses")
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chen-Yu Tsai <redacted>
---
 drivers/mmc/core/mmc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index c984321d1881..aafb73d080ca 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c

@@ -1276,7 +1276,7 @@ static int mmc_select_hs200(struct mmc_card *card)
         * switch to HS200 mode if bus width is set successfully.
         */
        err = mmc_select_bus_width(card);
-       if (!err) {
+       if (err > 0) {
                val = EXT_CSD_TIMING_HS200 |
                      card->drive_strength << EXT_CSD_DRV_STR_SHIFT;
                err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,

@@ -1583,7 +1583,7 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
        } else if (mmc_card_hs(card)) {
                /* Select the desired bus width optionally */
                err = mmc_select_bus_width(card);
-               if (!err) {
+               if (err > 0) {

As pointed out in the review by Bj?rn, to restore the old behaviour we
should check for "err >= 0".
No need to send a new patch, I can amend the current version.

quoted

                        err = mmc_select_hs_ddr(card);
                        if (err)
                                goto free_card;
--
2.8.1

Finally, I am a little concerned about the commit 287980e49ffc
("remove lots of IS_ERR_VALUE abuses") which introduced this
regression.

Surprisingly the IS_ERR_VALUE():s aren't being replaced by equivalent
checks, so perhaps there a more regressions. Moreover, I wonder why I
wasn't being on cc/to list when this patch was submitted a few days
ago, perhaps my review could prevented the regression from even
happen.

Anyway, let's fix this now! I will pick up $subject patch as fix asap...

and Arnd, can you please double-check that the commit 287980e49ffc
doesn?t seems to regress anything else!?

If only the 287980e49ffc could sit in linux-next for few days before
reaching v4.7-rc1... Could you please pick up the fix soon? Maybe
directly by Linus?

The fix has already been applied and published through my mmc tree. I
am waiting for reports from kernelci, assuming those will be okay, I
will send a PR tomorrow so it should reach rc2.

Kind regards
Uffe

Best regards,
Krzysztof