Re: [PATCH V2 2/2] mmc: mmci: initialize pwr|clk|datactrl_reg with their hardware values

[Ludovic BARRE]

hi Ulf

Le 3/26/20 Ã 3:27 PM, Ulf Hansson a ÃcritÂ:
> On Wed, 25 Mar 2020 at 15:34, Ludovic Barre <ludovic.barre@xxxxxx> wrote:
> > In mmci_write_pwr|clk|datactrlreg functions, if the desired value
> > is equal to corresponding variable (pwr_reg|clk_reg|datactrl_reg),
> > the value is not written in the register.
> >
> > At probe pwr|clk|datactrl_reg of mmci_host structure are initialized
> > to 0 (kzalloc of mmc_alloc_host). But they does not necessarily reflect
> > hardware value of these registers, if they are used while boot level.
> > This is problematic, if we want to write 0 in these registers.
>
> It could be, but I don't see that we ever needs to do that - at least
> not before we have written some other non-zero values to them (through
> the helper functions).

The sdmmc variant is slightly different on pwr_ctrl field
of MMCIPOWER register.

In classic mmci we have 3 or 2 values:
MMCI_PWR_OFF(0x0), MMCI_PWR_UP(0x2)optional, MMCI_PWR_ON(0x3)
-When you switch the external power supply off, the software set
 power-off (0x0).

-When you switch the external power supply on, the software first enters
 the power-up(0x2) phase, and waits until the supply output is stable
 before moving to the power-on (0x3)phase.

On sdmmc we have 3 values:
MMCI_PWR_OFF(0x0), MCI_STM32_PWR_CYC(0x2), MMCI_PWR_ON(0x3)
-When you switch the external power supply off, the software must
 MCI_STM32_PWR_CYC(0x2) => This will make that the SDMMC_D[7:0],
 SDMMC_CMD and SDMMC_CK are driven low, to prevent the card from being
 supplied through the signal lines.

-When you switch the external power supply on, when supply output is
 stable the MMCI_PWR_OFF(0x0) state can be apply (minimum 1ms) => The
 SDMMC_D[7:0], SDMMC_CMD and SDMMC_CK are set to drive â1â. After
 MMCI_PWR_ON(0x3) stat could be set.

In fact the last value of power off sequence is different between
classic and sdmmc:
The classic mmci finish the power off sequence by 0x0, But the sdmmc
finish by 0x2, and we must write 0x0 in power on sequence before set
MMCI_PWR_ON.
The 0x0 value is not written due to kzalloc value of pwr_reg
(which not reflect hardware value of pwr register).

> > This patch initializes pwr|clk|datactrl_reg variables with their
> > hardware values while probing.
>
> Hmm, so in principle this change seems quite okay, but I am hesitant
> to pick it up - unless it really addresses a problem that you have
> observed.
>
> The reason is, this change may lead to avoiding to re-write the
> register with the same value it got during boot - and who knows what
> is best here.

I understand your hesitation.
If you prefer, I can move the pwr_reg initialisation
in sdmmc_variant_init ?

Regards
Ludo

> Kind regards
> Uffe
>
> > Signed-off-by: Ludovic Barre <ludovic.barre@xxxxxx>
> > ---
> >   drivers/mmc/host/mmci.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
> > index 647567def612..f378ae18d5dc 100644
> > --- a/drivers/mmc/host/mmci.c
> > +++ b/drivers/mmc/host/mmci.c
> > @@ -2085,6 +2085,10 @@ static int mmci_probe(struct amba_device *dev,
> >          else if (plat->ocr_mask)
> >                  dev_warn(mmc_dev(mmc), "Platform OCR mask is ignored\n");
> >
> > +       host->pwr_reg = readl_relaxed(host->base + MMCIPOWER);
> > +       host->clk_reg = readl_relaxed(host->base + MMCICLOCK);
> > +       host->datactrl_reg = readl_relaxed(host->base + MMCIDATACTRL);
> > +
> >          /* We support these capabilities. */
> >          mmc->caps |= MMC_CAP_CMD23;
> >
> > --
> > 2.17.1