Increasing stabilization time in sunxi_mmc_core_init

[Jernej Škrabec]

Dne četrtek, 21. julij 2022 ob 21:56:35 CEST je Da Xue napisal(a):
> On Thu, Jul 21, 2022 at 11:14 AM Jernej Škrabec
> 
> <jernej.skrabec at gmail.com> wrote:
> > Hi!
> > 
> > Dne četrtek, 21. julij 2022 ob 13:28:59 CEST je Andre Przywara napisal(a):
> > > On 21/07/2022 12:03, Da Xue wrote:
> > > 
> > > Hi Da,
> > > 
> > > > Users were reporting non-boot on our H5 boards (ALL-H3-CC-H5). u-boot
> > > > gets stuck in SPL with this message for SD/eMMC respectively.
> > > > 
> > > > Trying to boot from MMC1 or Trying to boot from MMC2
> > > > 
> > > > I tested about 20 MicroSD cards from different brands and some were
> > > > happy and some were not. Increasing the udelay to 8-10ms in
> > > > drivers/mmc/sunxi_mmc.c sunxi_mmc_core_init after reset seems to fix
> > > > the issue for the MicroSD cards.
> > > 
> > > That's interesting, thanks for the report. I don't remember hearing of
> > > issues with MMC before, at least not in the SPL.
> > 
> > I certainly experienced this issue on board in question. I vaguely
> > remember
> > asking about this issue on IRC. I also tried all sorts of tweaks, but it
> > never occured to me that mmc reset timeout would be too short.
> > 
> > Da, how did you find this?
> 
> Someone on the Armbian forum posted that they had the same problem
> with eMMC so I got suspicious. I scoped the MicroSD clock line and
> realized the frequency goes high and then drops to very low as if it
> never found the card.
> I had a hunch it was a stabilization delay and got lucky.
> 
> > I only test one other H5 board occasionally, namely OrangePi PC2, but I
> > never observed such issue there. I always needed about 5 attempts to boot
> > ALL-H3-CC- H5 board, but once it's cold booted, warm boots always
> > succeed.
> 
> I had run into this too so it didn't make any sense. I tried 5ms and
> it helped on some cards but not others.
> I know the Orange Pis do not have the series resistor for ESD
> protection of the SD GPIOs but that shouldn't affect this.
> So...who knows?
> 
> > Best regards,
> > Jernej
> > 
> > > It's a bit odd that waiting after the *controller* reset should affect
> > > SD cards, and 1ms seems plenty for just the reset.
> > > I just checked and at least the SOFT_RESET and FIFO_RESET bits are self
> > > clearing. Can you try to use wait_for_bit_le32() to wait for those parts
> > > to finish? See sun8i_emac_eth_start() for an example.
> 
> I tested some more and here's the 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
> Given this, I don't think it's an issue with the bit set delays. Might
> need more than 10ms even. I didn't change the udelay in probe.

Idea here is that we wouldn't need to determine the appropriate delay, but 
instead, wait_for_bit_le32() would monitor reset bit and continue only after 
reset bit would clear itself. Hopefully that happens after everything is 
stable.

Best regards,
Jernej

> 
> > > And since you mentioned it's card related: can you check whether the
> > > delay is actually needed somewhere else, later? At some point where we
> > > wait to the card to response, for instance?
> > > 
> > > I am not against taking this patch, if it fixes problems for you, but
> > > just want to avoid that it papers over other issues.
> > > 
> > > Cheers,
> > > Andre
> > > 
> > > > Author: Da Xue <da at libre.computer>
> > > > Date:   Wed Jul 20 19:11:55 2022 -0400
> > > > 
> > > >      sunxi: raise stabilization time for mmc from 1ms to 8ms
> > > > 
> > > > diff --git a/drivers/mmc/sunxi_mmc.c b/drivers/mmc/sunxi_mmc.c
> > > > index 1bb7b6d0e9..499e057725 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(8000);
> 
> This might need to be even higher. Like 20ms.
> 
> > > >          return 0;
> > > >   
> > > >   }
> > > > 
> > > > I don't know the implications of this change so I am seeking feedback.
> > > > Are other boards having this issue as well or is it specific to our
> > > > hardware?
> > > > 
> > > > Best,
> > > > Da