Re: [PATCH 1/2] mmc: jz4740: Don't change parent clock rate for some SoCs

[Paul Cercueil]

Hi,

(Ingenic SoCs maintainer here)

Le ven. 18 nov. 2022 à 09:45:48 +0100, Ulf Hansson 
<ulf.hansson@xxxxxxxxxx> a écrit :
> On Tue, 8 Nov 2022 at 05:53, Siarhei Volkau <lis8215@xxxxxxxxx> wrote:
> >  Some SoCs have one clock divider for all MMC units, thus changing 
> > one
> >  affects others as well. This leads to random hangs and memory
> >  corruptions, observed on the JZ4755 based device with two MMC slots
> >  used at the same time.
>
> Urgh, that sounds like broken HW to me.
>
> The MMC blocks could share a parent clock (that would need a fixed
> rate for it to be applied), assuming there is a separate gate/divider
> available per block. But there isn't'?

They do share a parent clock and have separate gates, and each MMC IP 
block has an internal divider for the bus frequency derived from that 
shared clock.

> >  List of SoCs affected includes: JZ4725b, JZ4755, JZ4760 and JZ4760b.
> >  However, the MMC driver doesn't distinguish JZ4760 and JZ4770
> >  which shall remain its behavior. For the JZ4755 is sufficient to
> >  use JZ4725b's binding. JZ4750 is outside of the patch.
> >
> >  The MMC core has its own clock divisor, rather coarse but suitable 
> > well,
> >  and it shall keep the role of tuning clock for the MMC host in that
> >  case.
>
> The mmc core doesn't have a clock divisor, but it does control the bus
> clock frequency through the ->set_ios() host ops. It needs to do that,
> to be able to conform to the (e)MMC, SD and SDIO specifications.
>
> Can you please try to elaborate on the above, so I can better
> understand your point?

Yes, I don't really understand the patch, TBH.

The "clk_set_rate" call will only set the shared clock to the *maximum* 
clock frequency (host->mmc->f_max) which should be the exact same 
across all MMC IPs.

So it doesn't matter if it's set 3 times by 3 different instances of 
the IP, as long as they all request the same value.

Besides, I know for a fact that the mainline driver works fine on the 
JZ4760(B) and JZ4725B.

Finally... even if it was correct, this change would break 
compatibility with old Device Tree files.

Cheers,
-Paul

> >  Signed-off-by: Siarhei Volkau <lis8215@xxxxxxxxx>
>
> Kind regards
> Uffe
>
> >  ---
> >   drivers/mmc/host/jz4740_mmc.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> >  diff --git a/drivers/mmc/host/jz4740_mmc.c 
> > b/drivers/mmc/host/jz4740_mmc.c
> >  index dc2db9c18..d390ff31d 100644
> >  --- a/drivers/mmc/host/jz4740_mmc.c
> >  +++ b/drivers/mmc/host/jz4740_mmc.c
> >  @@ -114,6 +114,7 @@ enum jz4740_mmc_version {
> >          JZ_MMC_JZ4740,
> >          JZ_MMC_JZ4725B,
> >          JZ_MMC_JZ4760,
> >  +       JZ_MMC_JZ4770,
> >          JZ_MMC_JZ4780,
> >          JZ_MMC_X1000,
> >   };
> >  @@ -887,7 +888,13 @@ static int jz4740_mmc_set_clock_rate(struct 
> > jz4740_mmc_host *host, int rate)
> >          int real_rate;
> >
> >          jz4740_mmc_clock_disable(host);
> >  -       clk_set_rate(host->clk, host->mmc->f_max);
> >  +
> >  +       /*
> >  +        * Changing rate on these SoCs affects other MMC units too.
> >  +        * Make sure the rate is configured properly by the CGU 
> > driver.
> >  +        */
> >  +       if (host->version != JZ_MMC_JZ4725B && host->version != 
> > JZ_MMC_JZ4760)
> >  +               clk_set_rate(host->clk, host->mmc->f_max);
> >
> >          real_rate = clk_get_rate(host->clk);
> >
> >  @@ -992,6 +999,7 @@ static const struct of_device_id 
> > jz4740_mmc_of_match[] = {
> >          { .compatible = "ingenic,jz4740-mmc", .data = (void *) 
> > JZ_MMC_JZ4740 },
> >          { .compatible = "ingenic,jz4725b-mmc", .data = (void 
> > *)JZ_MMC_JZ4725B },
> >          { .compatible = "ingenic,jz4760-mmc", .data = (void *) 
> > JZ_MMC_JZ4760 },
> >  +       { .compatible = "ingenic,jz4770-mmc", .data = (void *) 
> > JZ_MMC_JZ4770 },
> >          { .compatible = "ingenic,jz4775-mmc", .data = (void *) 
> > JZ_MMC_JZ4780 },
> >          { .compatible = "ingenic,jz4780-mmc", .data = (void *) 
> > JZ_MMC_JZ4780 },
> >          { .compatible = "ingenic,x1000-mmc", .data = (void *) 
> > JZ_MMC_X1000 },
> >  --
> >  2.36.1