linux-kernel - Re: [PATCH] mmc: core: Fix mmc_select

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Date:	Tue, 7 Jun 2016 23:58:17 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Peter Griffin <peter.griffin@...aro.org>,
	Lee Jones <lee.jones@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kernel@...inux.com, Adrian Hunter <adrian.hunter@...el.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] mmc: core: Fix mmc_select_hs200() regression in v4.7-rc.

On 7 June 2016 at 15:57, Peter Griffin <peter.griffin@...aro.org> wrote:
> Hi Lee,
>
> On Tue, 07 Jun 2016, Lee Jones wrote:
>
>> On Tue, 07 Jun 2016, Peter Griffin wrote:
>>
>> > mmc_select_bus_width() returns bus width (4 or 8) on success or
>> > zero if unsupported. If bus width is set successfully we then wish
>> > to switch to HS200 mode.
>> >
>> > This avoids the following error message in v4.70-rc2
>> >
>> > [    2.523674] mmc0: mmc_select_hs200 failed, error 3
>> > [    2.528516] mmc0: error 3 whilst initialising MMC card
>> >
>> > With this patch card is enumerated correctly
>> >
>> > [    2.468065] mmc0: new HS200 MMC card at address 0001
>> > [    2.468335] mmcblk0: mmc0:0001 P1XXXX 7.20 GiB
>> > [    2.468441] mmcblk0boot0: mmc0:0001 P1XXXX partition 1 2.00 MiB
>> > [    2.468552] mmcblk0boot1: mmc0:0001 P1XXXX partition 2 2.00 MiB
>> > [    2.468651] mmcblk0rpmb: mmc0:0001 P1XXXX partition 3 128 KiB
>> > [    2.469269]  mmcblk0: p1
>> >
>> > Fixes: 287980e (remove lots of IS_ERR_VALUE abuses)
>> > Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
>> > Cc: Arnd Bergmann <arnd@...db.de>
>> > ---
>> >  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 c984321..aafb73d 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) {
>> >                     err = mmc_select_hs_ddr(card);
>> >                     if (err)
>> >                             goto free_card;
>>
>> Looks like this has already been 'fixed' in -rc2.
>
> Ah, it seems I was on -rc1, not -rc2
>
>>
>> Although, this patch does not work for me.
>>     mmc: fix mmc mode selection for HS-DDR and higher
>>
>>     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>
>>     Acked-by: Hans de Goede <hdegoede@...hat.com>
>>     Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
>>     Acked-by: Jaehoon Chung <jh80.chung@...sung.com>
>>     Reviewed-by: Shawn Lin <shawn.lin@...k-chips.com>
>>     Tested-by: Marcel Ziswiler <marcel.ziswiler@...adex.com>
>>     Tested-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>>     Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
>>
>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>> index c984321..5d438ad 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) {
>
>
> This patch looks wrong to me, as if zero is returned by mmc_select_bus_width() it
> means setting the bus width failed, and you most likely don't want to switch to
> hs200 mode.
>
> Ulf - what is your opinion?
>
> regards,
>
> Peter.>

The commit above (mmc: fix mmc mode selection for HS-DDR and higher),
simply restored the old behaviour and that was sufficient to solve the
regressions.

Nevertheless I agree, that if mmc_select_bus_width() returns 0, that
should likely mean that we shouldn't try to switch to hs200. If we
want to change that, let's do that in a separate patch on top.
So, do you see a problem in rc2?

Kind regards
Uffe