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

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Date:	Thu, 2 Jun 2016 11:35:24 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Chen-Yu Tsai <wens@...e.org>, Arnd Bergmann <arnd@...db.de>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher

On Thu, Jun 2, 2016 at 10:31 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> + Linus
>
> On 29 May 2016 at 09:04, Chen-Yu Tsai <wens@...e.org> wrote:
>> 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@...db.de>
>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>> ---
>>  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 Björn, to restore the old behaviour we
> should check for "err >= 0".
> No need to send a new patch, I can amend the current version.
>
>>                         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?

Best regards,
Krzysztof