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 09:45:48 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Siarhei Volkau <lis8215@...il.com>
Cc:     Paul Cercueil <paul@...pouillou.net>,
        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

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'?

>
> 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?

>
> 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
>