Re: Regression after "do not use CMD13 to get status after speed mode switch"

[Chaotian Jing <chaotian.jing@mediatek.com>]

On Wed, 2016-10-19 at 18:41 +0200, Ulf Hansson wrote:
> Adrian, Linus,
> 
> Thanks for looking into this and reporting!
> 
> On 18 October 2016 at 15:23, Adrian Hunter <adrian.hunter@intel.com> wrote:
> > On 18/10/16 11:36, Linus Walleij wrote:
> >> On Mon, Oct 17, 2016 at 4:32 PM, Linus Walleij <linus.walleij@linaro.org> wrote:
> >>
> >>> Before this patch the eMMC is detected and all partitions enumerated
> >>> immediately, but after the patch it doesn't come up at all, except
> >>> sometimes, when it appears minutes (!) after boot, all of a sudden.
> >>
> >> FYI this is what it looks like when it eventually happens:
> >> root@msm8660:/ [  627.710175] mmc0: new high speed MMC card at address 0001
> >> [  627.711641] mmcblk0: mmc0:0001 SEM04G 3.69 GiB
> >> [  627.715485] mmcblk0boot0: mmc0:0001 SEM04G partition 1 1.00 MiB
> >> [  627.736654] mmcblk0boot1: mmc0:0001 SEM04G partition 2 1.00 MiB
> >> [  627.747397] mmcblk0rpmb: mmc0:0001 SEM04G partition 3 128 KiB
> >> [  627.756326]  mmcblk0: p1 p2 p3 p4 < p5 p6 p7 p8 p9 p10 p11 p12 p13
> >> p14 p15 p16 p17 p18 p19 p20 p21 >
> >>
> >> So after 627 seconds, a bit hard for users to wait this long for their
> >> root filesystem.
> >
> > If the driver does not support busy detection and the eMMC card provides
> > zero as the cmd6 generic timeout (which it may especially as cmd6 generic
> > timeout wasn't added until eMMCv4.5), then __mmc_switch() defaults to
> > waiting 10 minutes i.e.
> >
> > #define MMC_OPS_TIMEOUT_MS      (10 * 60 * 1000) /* 10 minute timeout */
> 
> Urgh! Yes, I have verified that this is exactly what happens.
> 
> >
> > So removal of CMD13 polling for HS mode (as per commit
> > 08573eaf1a70104f83fdbee9b84e5be03480e9ed) is going to be a problem for some
> > combinations of eMMC cards and host drivers.
> 
> I was looking in the __mmc_switch() function, it's just a pain to walk
> trough it :-) So first out I decided to clean it up and factor out the
> polling parts. I will post the patches first out tomorrow morning,
> running some final test right now.
> 
> Although, that of course doesn't solve our problem. As I see it we
> only have a few options here.
> 
> 1) In case when cmd6 generic timeout isn't available, let's assign
> another empirically selected value.
> 2) Use a specific timeout when switching to HS mode.
> 3) Even if we deploy 1 (and 2), perhaps we still should allow polling
> with CMD13 for switching to HS mode - unless it causes issues for some
> cards/drivers combination?
> 
> BTW, I already tried 2) and it indeed solves the problem, although
> depending on the selected timeout, it might delay the card detection
> to process.
> 
> Thoughts?

I just have a try of switching to HS mode with Hynix EMMC, the first
CMD13 gets response of 0x900, but the EMMC is still pull-low DAT0. so
that CMD13 cannot indicate current card status in this case.
> 
> Kind regards
> Uffe