Re: [PATCH] mmc: usdhi6rol0: Implement card_busy function

[Marten Lindahl <martenli@axis.com>]

Hi Ulf!

Thank you for your comments! I will update the patch.

On Fri, Aug 13, 2021 at 11:25:35AM +0200, Ulf Hansson wrote:
> On Thu, 12 Aug 2021 at 16:51, Mårten Lindahl <marten.lindahl@axis.com> wrote:
> >
> > When switching card voltage to UHS voltage the mmc framework tries to
> > check that the card is driving pins CMD, and DAT[0-3] low before the
> > switch is made. Drivers that does not implement the card_busy function
> > will manage to do the switch anyway, but the framework will print a
> > warning about not being able to verify the voltage signal.
> >
> > Implement card_busy function. Renesas host interface only exposes pins
> > DAT[0] and DAT[3] for reading the busy state, which is why only these
> > two pins are checked.
> >
> > Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
> > ---
> >  drivers/mmc/host/usdhi6rol0.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > diff --git a/drivers/mmc/host/usdhi6rol0.c b/drivers/mmc/host/usdhi6rol0.c
> > index b9b79b1089a0..e400a646e675 100644
> > --- a/drivers/mmc/host/usdhi6rol0.c
> > +++ b/drivers/mmc/host/usdhi6rol0.c
> > @@ -77,6 +77,7 @@
> >  #define USDHI6_SD_INFO1_WP             BIT(7)
> >  #define USDHI6_SD_INFO1_D3_CARD_OUT    BIT(8)
> >  #define USDHI6_SD_INFO1_D3_CARD_IN     BIT(9)
> > +#define USDHI6_SD_INFO1_SDDAT3         BIT(10)
> >
> >  #define USDHI6_SD_INFO2_CMD_ERR                BIT(0)
> >  #define USDHI6_SD_INFO2_CRC_ERR                BIT(1)
> > @@ -1186,6 +1187,21 @@ static int usdhi6_sig_volt_switch(struct mmc_host *mmc, struct mmc_ios *ios)
> >         return ret;
> >  }
> >
> > +static int usdhi6_card_busy(struct mmc_host *mmc)
> > +{
> > +       struct usdhi6_host *host = mmc_priv(mmc);
> > +       u32 info1 = usdhi6_read(host, USDHI6_SD_INFO1);
> > +       u32 info2 = usdhi6_read(host, USDHI6_SD_INFO2);
> > +
> > +       /* Check if the SD bus is processing a command */
> 
> Hmm, this sounds a bit confusing to me. Don't you want to say
> something like "the clock logic is enabled".
> 
> The point is, from the mmc core point of view, ->card_busy() is called
> to poll for busy completion *after* a command has been processed.
> 

Thanks. After reading the SD specification my understanding is that it
should be enough to solely check DAT0 in this case. I will remove the
check for SCLKDIVEN.

> > +       if (!(info2 & USDHI6_SD_INFO2_SCLKDIVEN))
> > +               return 0;
> > +
> > +       /* Card is busy if it is pulling dat[0] & dat[3] low */
> > +       return !(info2 & USDHI6_SD_INFO2_SDDAT0 ||
> > +                info1 & USDHI6_SD_INFO1_SDDAT3);
> 
> In fact, it's sufficient to monitor any one of the DATA lines to check
> for busy for the UHS-I switch, according to the SD spec.
> 
> However, since we are using ->card_busy() to monitor also other busy
> signal scenarios, like for some commands with R1B responses that
> assert only DAT0 to signal busy (at least according to specs), I think
> it's better to monitor solely DAT0 here.
> 

I will remove the check for DAT3.

> I realize that the comment for the ->card_busy() callback in
> include/linux/mmc/host.h needs to be updated to clarify this as well.
> 

I will update the card_busy callback comment to DAT0 only.

Kind regards
Mårten

> > +}
> > +
> >  static const struct mmc_host_ops usdhi6_ops = {
> >         .request        = usdhi6_request,
> >         .set_ios        = usdhi6_set_ios,
> > @@ -1193,6 +1209,7 @@ static const struct mmc_host_ops usdhi6_ops = {
> >         .get_ro         = usdhi6_get_ro,
> >         .enable_sdio_irq = usdhi6_enable_sdio_irq,
> >         .start_signal_voltage_switch = usdhi6_sig_volt_switch,
> > +       .card_busy = usdhi6_card_busy,
> >  };
> >
> >  /*                     State machine handlers                          */
> > --
> > 2.20.1
> >
> 
> Kind regards
> Uffe