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

Ulf Hansson
2021-02-23T11:59:37Z

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?

Kind regards
Uffe