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

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

On Wed, Jun 10, 2026 at 11:21:53AM +0300, Vladimir Zapolskiy wrote:
> FWIW due to https://www.nxp.com/docs/en/data-sheet/IW416.pdf "10.7.1 VIO_SD
> DC characteristics" SDR104 speed mode is not supported by the module, thus
> the selection of the SDR50 speed mode on the host side sounds to be correct
> in your case.
> 
> In SDR50 speed mode gcc_sdcc4_apps_clk clock frequency should be exactly
> 100MHz, and since it differs, it has an impact during the tuning phase.
> 
> Definitely clk/qcom/gcc-sm8550.c says that the maximum supported frequency
> is 75MHz, the same is found in the downstream v5.15 kernel:
> 
> static const struct freq_tbl ftbl_gcc_sdcc4_apps_clk_src[] = {
>         F(400000, P_BI_TCXO, 12, 1, 4),
>         F(25000000, P_GCC_GPLL0_OUT_EVEN, 12, 0, 0),
>         F(37500000, P_GCC_GPLL0_OUT_EVEN, 8, 0, 0),
>         F(75000000, P_GCC_GPLL0_OUT_EVEN, 4, 0, 0),
>         { }
> };
> 
> Can you dump CAPS1 register value of SM8550 SDHC4? What does it say about
> SDR50 mode support and need for SDR50 mode tuning?
> 
> -- 
> Best wishes,
> Vladimir
CAPS0 and CAPS1 are below:
  sdhci_msm 8844000.mmc: CAPS0: 0x3029c8b2 CAPS1: 0x0000a08b
For CAPS1: 
  Bit 0 (SDR50 support) = 1
  Bit 13 (Use Tuning for SDR50) = 1
It looks to report that SDR50 is supported with tuning required.

Best regards,
Will