Re: [PATCH 3/3] mmc: core: Default to generic_cmd6_time as timeout in __mmc_switch()

[Ulf Hansson <ulf.hansson@linaro.org>]

On Tue, 23 Feb 2021 at 14:42, Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> On 23/02/21 1:54 pm, Ulf Hansson wrote:
> > On Tue, 23 Feb 2021 at 12:19, Paul Fertser <fercerpav@gmail.com> wrote:
> >>
> >> Hello Adrian,
> >>
> >> On Tue, Feb 23, 2021 at 01:01:09PM +0200, Adrian Hunter wrote:
> >>> On 23/02/21 11:32 am, Paul Fertser wrote:
> >>>> Hello Ulf,
> >>>>
> >>>> On Tue, Feb 23, 2021 at 10:23:28AM +0100, Ulf Hansson wrote:
> >>>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> >>>>>> index f5dedb7f9b27..9adf735391fa 100644
> >>>>>> --- a/drivers/mmc/core/mmc.c
> >>>>>> +++ b/drivers/mmc/core/mmc.c
> >>>>>> @@ -426,8 +426,7 @@ static int mmc_decode_ext_csd(struct mmc_card *card, u8 *ext_csd)
> >>>>>>                 /* EXT_CSD value is in units of 10ms, but we store in ms */
> >>>>>>                 card->ext_csd.part_time = 10 * ext_csd[EXT_CSD_PART_SWITCH_TIME];
> >>>>>>                 /* Some eMMC set the value too low so set a minimum */
> >>>>>> -               if (card->ext_csd.part_time &&
> >>>>>> -                   card->ext_csd.part_time < MMC_MIN_PART_SWITCH_TIME)
> >>>>>> +               if (card->ext_csd.part_time < MMC_MIN_PART_SWITCH_TIME)
> >>>>>>                         card->ext_csd.part_time = MMC_MIN_PART_SWITCH_TIME;
> >>>>>>
> >>>>>>                 /* Sleep / awake timeout in 100ns units */
> >>>>>>
> >>>>>> I do not see any more warnings on my system.
> >>>>>
> >>>>> That looks like the correct fix to the problem. Do you want to send a
> >>>>> proper patch that I can pick up or do you prefer if help to do it?
> >>>>
> >>>> I've sent this as a diff precisely because 1c447116d017 was so
> >>>> explicit about special-casing zero ext_csd timeout value, so I thought
> >>>> probably Adrian can provide the rationale for that. I'd prefer to wait
> >>>> for his feedback before sending a formal patch. Does this make sense?
> >>>
> >>> Zero means indefinite.  Might be safer to use a higher value than
> >>> MMC_MIN_PART_SWITCH_TIME for that case.  The maximum GENERIC_CMD6_TIME is
> >>> 2550 ms.
> >>
> >> Thanks for the clarification! I would guess that most likely than not
> >> when whoever defines that value to be zero it means "I do not
> >> care/know" rather than "the timeout must be set to more than 2550 ms,
> >> too bad 8 bits are not enough to represent that". I'd say setting it
> >> to DEFAULT_CMD6_TIMEOUT_MS should be safe enough since it worked
> >> before.
> >
> > Hmm.
> >
> > The DEFAULT_CMD6_TIMEOUT_MS is intended to override the
> > ext_csd->generic_cmd6_time, in case it's not defined in the register.
> >
> > Perhaps it's reasonable to think that eMMC vendors specify the
> > GENERIC_CMD6_TIME, but may skip to specify other timeouts, like the
> > PARTITION_SWITCH_TIME. In that case, should we use the specified
> > GENERIC_CMD6_TIME, rather than always default to
> > DEFAULT_CMD6_TIMEOUT_MS?
>
> Sounds reasonable, but perhaps still enforce a minimum, for some of the same
> reasons as commit 1c447116d017 ?
> e.g.
>
>         if (!card->ext_csd.part_time)
>                 card->ext_csd.part_time = card->ext_csd.generic_cmd6_time;
>         if (card->ext_csd.part_time < MMC_MIN_PART_SWITCH_TIME)
>                 card->ext_csd.part_time = MMC_MIN_PART_SWITCH_TIME;
>

Makes perfect sense to me!

Kind regards
Uffe