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

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Date:   Fri, 18 Nov 2022 12:51:54 +0300
From:   Siarhei Volkau <lis8215@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH 1/2] mmc: jz4740: Don't change parent clock rate for some SoCs

пт, 18 нояб. 2022 г. в 12:27, Paul Cercueil <paul@...pouillou.net>:
>
> Hi,
>
> (Ingenic SoCs maintainer here)
>
> Le ven. 18 nov. 2022 à 09:45:48 +0100, Ulf Hansson
> <ulf.hansson@...aro.org> a écrit :
> > On Tue, 8 Nov 2022 at 05:53, Siarhei Volkau <lis8215@...il.com> 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.

That's the case I need different "f_max" for my HW, for some reason
internal slot can't do a full rate (48MHz) but the external can, the same
card used for checking. So I want to set 24M for mmc0, and 48M for mmc1
with respect to hardware limitation.

>
> 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@...il.com>
> >
> > 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
> >>
>
>