Re: [PATCH] sunxi-mmc: increase stabilization delay from 1ms to 20ms

[Da Xue <da@libre.computer>]

On Fri, Jul 22, 2022 at 1:56 PM Jernej Škrabec <jernej.skrabec@gmail.com> wrote:
>
> Dne petek, 22. julij 2022 ob 18:55:14 CEST je Andre Przywara napisal(a):
> > On 21/07/2022 23:08, Da Xue wrote:
> >
> > Hi,
> >
> > > Some users experienced problems booting u-boot from SPL hanging here:
> > >
> > > Trying to boot from MMC1 or Trying to boot from MMC2
> > >
> > > This seems to occur with both MicroSD and eMMC modules on ALL-H3-CC.
> > > Increasing the delay after mmc reset fixes these boot problems.
> > > Some MicroSD cards are impacted more than others so it is possible that
> > > MicroSD internals need time to stabilize. Below is some failure data.
> > >
> > > sandisk ultra   64gb 9/20 with 1ms,  20/20 with 10ms
> > > sandisk ultra   16gb 2/20 with 1ms,  20/20 with 10ms
> > > sandisk extreme 16gb 6/20 with 10ms, 20/20 with 20ms
> > >
> > > A quick comparison of schematics show series resistors for ESD
> > > protection on the MicroSD GPIOs not present on all H3/H5 boards.
> > > It is not known if this is related to the issue.
> > >
> > > This patch adds a fixed 20ms delay to mmc init to mitigate the problem.
> > > If boot time optimization is required and the platform does not require
> > > the delay. The delay can be replaced with:
> > >
> > > writel(SUNXI_MMC_GCTRL_RESET, &priv->reg->gctrl);
> > > if (wait_for_bit_le32( &priv->reg->gctrl,
> > > SUNXI_MMC_GCTRL_RESET, false, 20, false)) {
> > > printf("%s: Timeout\n", __func__);
> > > return -ETIMEDOUT;
> > > }
> >
> > So what about adding this for everyone (we should have it regardless) then?

I think it would be good to add for everyone. This only happens in SPL
so the impact is limited in terms of time cost.

> >
> > And then have an extra Kconfig option to specify an extra delay, and
> > define this only in your board defconfig? Because IIUC this is specific
> > to your board?

I only have my boards to test. I'm sure there are other devices that have the
same issue. I don't think it's exclusive to our boards.

> >
> > And as I mentioned: it looks odd to have this here and have it fixing
> > your SD card problems:
> > - The soft reset should reset just the internal controller logic (MMC
> > state machine and FIFOs), this shouldn't affect cards. IIUC, nothing
> > should happen on the MMC *pins* because of this operation.
> > - Why isn't this a problem for U-Boot proper, and Linux, FWIW?
>
> As I said before, I have issue only at cold boot in SPL. Once I pass this
> point, it works all the time, even if rebooted. Why is that so it's unclear.
>
> Thinking about this a bit, I have another question. How is it possible that
> BROM manages to read SD card just fine and loads SPL beforehand? Is it using
> lower speed? It also couldn't be power issue, since card must have been
> properly powered up by BROM...

Is the bootrom using SPI mode on first boot? If that is the case, a transition
would take time and may explain the necessity of this.

>
> Best regards,
> Jernej
>
> >
> > Cheers,
> > Andre
> >
> > > Signed-off-by: Da Xue <da@libre.computer>
> > > ---
> > >
> > >   drivers/mmc/sunxi_mmc.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/mmc/sunxi_mmc.c b/drivers/mmc/sunxi_mmc.c
> > > index 1bb7b6d0e9..f7942b69ce 100644
> > > --- a/drivers/mmc/sunxi_mmc.c
> > > +++ b/drivers/mmc/sunxi_mmc.c
> > > @@ -297,7 +297,7 @@ static int sunxi_mmc_core_init(struct mmc *mmc)
> > >
> > >    /* Reset controller */
> > >    writel(SUNXI_MMC_GCTRL_RESET, &priv->reg->gctrl);
> > >
> > > - udelay(1000);
> > > + udelay(20000);
> > >
> > >    return 0;
> > >
> > >   }
>
>
>
>