Re: [PATCH] drm/msm/mdss: Add a TODO for better managing the MDSS clock power state

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Tue, Mar 10, 2026 at 02:20:25PM +0100, Konrad Dybcio wrote:
> From: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> 
> There's a small window where the MDP clock could be set to a high rate
> (say, from the bootloader) without a corresponding RPM(H)PD vote to
> back it up. This is normally not an issue, but could be, if rmmod fails
> to shut down the display driver cleanly, and the module is inserted
> again, or when the providers' .sync_state has timed out.
> 
> Mark a TODO to fix it one day. Linking the relevant discussion below.
> 
> Link: https://lore.kernel.org/linux-arm-msm/d5c4eed5-bd87-4156-b178-2d78140ec8a9@oss.qualcomm.com/
> Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> ---
>  drivers/gpu/drm/msm/msm_mdss.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/msm_mdss.c b/drivers/gpu/drm/msm/msm_mdss.c
> index 9047e8d9ee89..b783dfec83b8 100644
> --- a/drivers/gpu/drm/msm/msm_mdss.c
> +++ b/drivers/gpu/drm/msm/msm_mdss.c
> @@ -262,6 +262,14 @@ static int msm_mdss_enable(struct msm_mdss *msm_mdss)
>  	icc_set_bw(msm_mdss->reg_bus_path, 0,
>  		   msm_mdss->reg_bus_bw);
>  
> +	/*
> +	 * TODO:
> +	 * Previous users (e.g. the bootloader) may have left this clock at a high rate, which
> +	 * would remain set, as prepare_enable() doesn't reprogram it. This theoretically poses a
> +	 * risk of brownout, but realistically this path is almost exclusively excercised after the
> +	 * correct OPP has been set in one of the MDPn or DPU drivers, or during initial probe,
> +	 * before the RPM(H)PD sync_state is done.
> +	 */

I'd have preferred if it was not exercising 100-char limit, but there is
no reason to enforce that.


Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

>  	ret = clk_bulk_prepare_enable(msm_mdss->num_clocks, msm_mdss->clocks);
>  	if (ret) {
>  		dev_err(msm_mdss->dev, "clock enable failed, ret:%d\n", ret);
> 
> ---
> base-commit: fc7b1a72c6cd5cbbd989c6c32a6486e3e4e3594d
> change-id: 20260310-topic-mdss_power_todo-4a19cf5f5183
> 
> Best regards,
> -- 
> Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> 

-- 
With best wishes
Dmitry