Re: [PATCH 1/2] arm64: dts: mediatek: mt8192: Make sure MSDCPLL's rate is 400MHz

[Matthias Brugger <matthias.bgg@gmail.com>]

On 15/06/2023 11:51, TingHan Shen (沈廷翰) wrote:
> Hi AngeloGioacchino,
> 
> On Mon, 2023-05-22 at 11:30 +0200, AngeloGioacchino Del Regno wrote:
>> External email : Please do not click links or open attachments until you have verified the sender or the content.
>>
>>
>> Some bootloaders will set MSDCPLL's rate lower than 400MHz: what I have
>> seen is this clock being set at around 384MHz.
>> This is a performance concern (and possibly a stability one, for picky
>> eMMC/SD cards) as the MSDC controller's internal divier will choose a
>> frequency that is lower than expected, in the end causing a difference
>> in the expected mmc/sd device's timings.
>>
>> Make sure that the MSDCPLL frequency is always set to 400MHz to both
>> improve performance and reliability of the sd/mmc storage.
>>
>> Fixes: 5d2b897bc6f5 ("arm64: dts: mediatek: Add mt8192 clock controllers")
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
>> ---
>>   arch/arm64/boot/dts/mediatek/mt8192.dtsi | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/mediatek/mt8192.dtsi b/arch/arm64/boot/dts/mediatek/mt8192.dtsi
>> index 5c30caf74026..6fc14004f6fd 100644
>> --- a/arch/arm64/boot/dts/mediatek/mt8192.dtsi
>> +++ b/arch/arm64/boot/dts/mediatek/mt8192.dtsi
>> @@ -677,6 +677,8 @@ apmixedsys: syscon@1000c000 {
>>                          compatible = "mediatek,mt8192-apmixedsys", "syscon";
>>                          reg = <0 0x1000c000 0 0x1000>;
>>                          #clock-cells = <1>;
>> +                       assigned-clocks = <&apmixedsys CLK_APMIXED_MSDCPLL>;
>> +                       assigned-clock-rates = <400000000>;
>>                  };
>>
>>                  systimer: timer@10017000 {
>> --
>> 2.40.1
>>
> 
> Comment from mtk emmc owner,
> 
> "As we all know, the clock has some jitter, when we set MSDCPLL to 400M,
> but the actual measurement is not exactly 200M.
> For eMMC, the spec stipulates that clock cannot exceed 200M.
> If MSDCPLL is set to 400M, the actual measurement may exceed the spec.
> So we set MSDCPLL to 384M in the bootloader stage to avoid exceeding the spec."
> 

Thanks for the feedback. Given that I'm not aware of any regressions that got 
fixed by this commits I will drop this series for now. We can keep on the 
discussion and if needed add them in a later stage.

Regards,
Matthias