linux-kernel - Re: [PATCH v2 2/2] dmaengine: JZ4780: Add support for the JZ4755.

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Message-Id: <A8AYJR.RL4SZCGLT3BZ1@crapouillou.net>
Date:   Tue, 18 Oct 2022 14:16:58 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Siarhei Volkau <lis8215@...il.com>
Cc:     Vinod Koul <vkoul@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH v2 2/2] dmaengine: JZ4780: Add support for the JZ4755.

Hi,

Le lun., oct. 17 2022 at 20:29:27 +0300, Siarhei Volkau 
<lis8215@...il.com> a écrit :
> пн, 17 окт. 2022 г. в 12:34, Paul Cercueil 
> <paul@...pouillou.net>:
>>  Can you verify that?
>> 
>>  It should be pretty simple, if it has the bug you'll see I/O errors 
>> on
>>  the SD card.
> 
> Well, the result is ambiguous:
> 
> Without that 'broken' flag: mmc works poorly, but becomes more or less
> stable when MMC clock downs to 6MHz (90% boots without errors).
> On the 12MHz MMC clock the issue doesn't appear in 50-70% cases.
> On the 24MHz MMC clock the device never boots up.
> 
> However with the flag: MMC works stable on 24MHz MMC clock
> (boot issue observed only once), but if I increase MMC clock speed 
> even
> a bit the problem appears oftenly ( >70% of cases).
> 
> So, that flag definitely helps a lot, but the nature of the problem 
> might be
> different.

If the flag makes any difference then it's needed.

The controller should support up to 50 MHz, make sure that your "mmc" 
clock is at 50 MHz otherwise changing the max-frequency DT property 
won't do much.

Cheers,
-Paul