Re: [PATCH v2] arm64: dts: qcom: sm8550: add SDHC4 controller node

[William Bright <william.bright@imd-tec.com>]

On Thu, Jun 11, 2026 at 10:48:34AM +0300, Vladimir Zapolskiy wrote:
> Looks like the SDHC driver behaves expectedly then. For me it's hard to say
> what may be the rootcause, I believe the lower bus frequency should be fine,
> so it sounds like a hardware issue, but could it be PCB/board specific one?
> 
> If you find a chance to copy the SDHC driver (and its small dependencies)
> from Android and test it on your board, and if it also fails, then it might
> be well concluded that something is wrong with hardware, still it won't be
> quite convincing that the SoC SDHC is to blame here.
> 
> Hope it helps.
> 
> -- 
> Best wishes,
> Vladimir
My colleague Tendai (<tendai.makumire@imd-tec.com>) had the same issue
with dll-tuning failing in SDR50 when working on the downstream 5.15 msm
kernel [1].
It does sound like a potential SI issue so I will try the following:
  - Sweeping the drive-strength values for the sdhc_4 lines to see if I
    can find a set of values that work
  - Scoping the lines to check SI when performing dll-tuning, our board
    is very dense so this is challenging.
I am guessing this patch is only acceptable to be upstreamed once we get
to the bottom of why dll-tuning is failing?

[1] https://github.com/imd-tec/meta-imdt-qcom/tree/kirkstone/patches/msm-kernel/files

Many thanks,
Will