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 09:27:05 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Siarhei Volkau <lis8215@...il.com>
Cc:     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

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.

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
>>