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

Le lun., oct. 17 2022 at 20:29:27 +0300, Siarhei Volkau=20
<lis8215@gmail.com> a =C3=A9crit :
> =D0=BF=D0=BD, 17 =D0=BE=D0=BA=D1=82. 2022 =D0=B3. =D0=B2 12:34, Paul Cerc=
ueil=20
> <paul@crapouillou.net>:
>>  Can you verify that?
>>=20
>>  It should be pretty simple, if it has the bug you'll see I/O errors=20
>> on
>>  the SD card.
>=20
> Well, the result is ambiguous:
>=20
> 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.
>=20
> However with the flag: MMC works stable on 24MHz MMC clock
> (boot issue observed only once), but if I increase MMC clock speed=20
> even
> a bit the problem appears oftenly ( >70% of cases).
>=20
> So, that flag definitely helps a lot, but the nature of the problem=20
> 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"=20
clock is at 50 MHz otherwise changing the max-frequency DT property=20
won't do much.

Cheers,
-Paul