Re: [PATCH] mmc: enable UHS voltage switch for SDSC if supported

[Ulf Hansson]

On Wed, 5 May 2021 at 14:13, Christian Löhle <CLoehle@xxxxxxxxxxxxxx> wrote:
>
> So two cards that advertise UHS:
> https://www.euric.de/de/flash-speicher/sd-microsd/sd/
> Model SDI790
> and
> https://na.industrial.panasonic.com/products/storage-media/industrial-sd-cards/lineup/industrial-grade-2d-nand/series/71695

Thanks for the links!

Are these the ones that you have been using for testing?

> Hopefully that suffices as a couple, otherwise I would buy some
> that do not advertise it and actually check if they support it anyway.
> But 2GB SLC listings are kind of rare these days, so it's not as
> easy to find many that are still sold and available.

Right. I have a whole bunch of old SD cards that I can test. I will
let you know when I have got some time to test some of them.

The main worry (but I may be wrong) I have with the patch is that it
could cause problems for other older SDSC cards, which happens to
incorrectly set the S18A bit. I mean, before UHS-I was introduced in
the SD spec, this bit was just being reserved and potentially it could
have *any* value by the card manufacturer. As I said, let me do some
tests of my older SD cards.

>
> My point about deviating from the standard was that these cards
> are already initialized as UHS, they just don't do the voltage switch.
> So anything reserved for UHS-I (e.g. CMD23 )is already being done
> by the host with the current linux-mmc,
> so the standard deviation is already there.
> Just the voltage switch is missing.

Ah, yes you are right!

We call mmc_sd_init_uhs_card() no matter whether the CCS bit is set.
Certainly this is a bug. Both the card and host aren't designed to
work under these conditions/timings.

>
> Regards,
> Christian
>

Kind regards
Uffe

>
> From: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> Sent: Wednesday, May 5, 2021 12:09 PM
> To: Christian Löhle <CLoehle@xxxxxxxxxxxxxx>
> Subject: Re: [PATCH] mmc: enable UHS voltage switch for SDSC if supported
>
> On Thu, 22 Apr 2021 at 15:18, Christian Löhle <CLoehle@xxxxxxxxxxxxxx> wrote:
> >
> > Ignore the reported capacity if the card otherwise reports UHS support.
> >
> > Currently SDSC cards reporting UHS support except for the CCS do not run
> > through the voltage switch.
> > While strictly speaking a SDSC card cannot support UHS in compliance
> > with the standard, there is no good reason to throttle them that way.
>
> Maybe not, but I think the code just tries to conform to the SD spec.
>
> > Especially for pSLCs in practice such cards benefit greatly by this patch,
> > as they can be new and UHS supporting, but must not lie about their CCS.
>
> Can you provide some concrete examples of SDSC cards that support UHS-I?
>
> > The behaviour of linux-mmc for SDSC is deviating from the standard anyway
> > in such a case, as the card is treated as UHS card not supporting the
> > voltage switch in general.
> > Such a card will come up as
> > mmc0: new ultra high speed SDR25 SD card at address 0001.
> > Thus the subsystem will support CMD23 and others to the card.
> > But if we deviate from the standard anyway, then we might as well
> > not throttle SDSC to 25MB/s.
>
> Not sure I understand this correctly? Can you elaborate a bit more, so
> I understand how we deviate from the SD spec here?
>
> As far as I understand the spec, SDSC cards shouldn't support UHS-I.
> If we decide to deviate from the spec to support this anyway, at least
> we need to know about a couple of cards that actually supports this.
>
> Kind regards
> Uffe
>
> >
> > Signed-off-by: Christian Loehle <cloehle@xxxxxxxxxxxxxx>
> > ---
> >  drivers/mmc/core/sd.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> > index 6fa51a6ed058..281ca2da8e0b 100644
> > --- a/drivers/mmc/core/sd.c
> > +++ b/drivers/mmc/core/sd.c
> > @@ -841,11 +841,10 @@ int mmc_sd_get_cid(struct mmc_host *host, u32 ocr, u32 *cid, u32 *rocr)
> >                 return err;
> >
> >         /*
> > -        * In case CCS and S18A in the response is set, start Signal Voltage
> > -        * Switch procedure. SPI mode doesn't support CMD11.
> > +        * In case S18A in the response is set, start Signal Voltage Switch
> > +        * procedure. SPI mode doesn't support CMD11.
> >          */
> > -       if (!mmc_host_is_spi(host) && rocr &&
> > -          ((*rocr & 0x41000000) == 0x41000000)) {
> > +       if (!mmc_host_is_spi(host) && rocr && (*rocr & 0x01000000)) {
> >                 err = mmc_set_uhs_voltage(host, pocr);
> >                 if (err == -EAGAIN) {
> >                         retries--;
> > --
> > 2.31.1
> >
> > Hyperstone GmbH | Line-Eid-Strasse 3 | 78467 Konstanz
> > Managing Directors: Dr. Jan Peter Berns.
> > Commercial register of local courts: Freiburg HRB381782
> >
>
> Hyperstone GmbH | Line-Eid-Strasse 3 | 78467 Konstanz
> Managing Directors: Dr. Jan Peter Berns.
> Commercial register of local courts: Freiburg HRB381782
>