Re: [PATCH 2/3] arm64: dts: qcom: sm8550: Enable UHS-I SDR50 and SDR104 SD card modes

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 11/26/25 2:20 AM, Vladimir Zapolskiy wrote:
> The restriction on UHS-I speed modes was added to all SM8550 platforms
> by copying it from SM8450 dtsi file, and due to the overclocking of SD
> cards it was an actually reproducible problem. Since the latter issue
> has been fixed, UHS-I speed modes are working fine on SM8550 boards,
> below is the test performed on SM8550-HDK:
> 
> SDR50 speed mode:
> 
>     mmc0: new UHS-I speed SDR50 SDHC card at address 0001
>     mmcblk0: mmc0:0001 00000 14.6 GiB
>      mmcblk0: p1
> 
>     % dd if=/dev/mmcblk0p1 of=/dev/null bs=1M count=1024
>     1024+0 records in
>     1024+0 records out
>     1073741824 bytes (1.1 GB, 1.0 GiB) copied, 23.5468 s, 45.6 MB/s
> 
> SDR104 speed mode:
> 
>     mmc0: new UHS-I speed SDR104 SDHC card at address 59b4
>     mmcblk0: mmc0:59b4 USDU1 28.3 GiB
>      mmcblk0: p1
> 
>     % dd if=/dev/mmcblk0p1 of=/dev/null bs=1M count=1024
>     1024+0 records in
>     1024+0 records out
>     1073741824 bytes (1.1 GB, 1.0 GiB) copied, 11.9819 s, 89.6 MB/s
> 
> Unset the UHS-I speed mode restrictions from the SM8550 platform dtsi
> file, there is no indication that the SDHC controller is broken.
> 
> Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
> ---

8550 has additional limitations. One was addressed recently with
max-sd-hs-hz (HS mode can only run at 37.5 MHz), but when in SDR104,
the frequency must also be capped to 148 MHz. I don't know whether
the driver respects that today.

Konrad