Re: [PATCH] drm: msm: a6xx: fix gpu failure after system resume

[Jordan Crouse <jcrouse@codeaurora.org>]

On Tue, Jul 14, 2020 at 06:55:30PM +0530, Akhil P Oommen wrote:
> On targets where GMU is available, GMU takes over the ownership of GX GDSC
> during its initialization. So, take a refcount on the GX PD on behalf of
> GMU before we initialize it. This makes sure that nobody can collapse the
> GX GDSC once GMU owns the GX GDSC. This patch fixes some weird failures
> during GPU wake up during system resume.

The change looks fine but this explanation is confusing. When I read it I
thought "oh, man, we weren't taking a reference to the GX PD during resume???"
but that's not really the case. We *are* taking a reference, just not soon
enough to avoid possible issues. It would be helpful if you reworded this to
explain that you are moving the reference and perhaps to shine a bit more light
on what the "weird" failures are.

Jordan

> Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> index a6f43ff..5b2df7d 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> @@ -873,10 +873,19 @@ int a6xx_gmu_resume(struct a6xx_gpu *a6xx_gpu)
>  	/* Turn on the resources */
>  	pm_runtime_get_sync(gmu->dev);
>  
> +	/*
> +	 * "enable" the GX power domain which won't actually do anything but it
> +	 * will make sure that the refcounting is correct in case we need to
> +	 * bring down the GX after a GMU failure
> +	 */
> +	if (!IS_ERR_OR_NULL(gmu->gxpd))
> +		pm_runtime_get_sync(gmu->gxpd);
> +
>  	/* Use a known rate to bring up the GMU */
>  	clk_set_rate(gmu->core_clk, 200000000);
>  	ret = clk_bulk_prepare_enable(gmu->nr_clocks, gmu->clocks);
>  	if (ret) {
> +		pm_runtime_put(gmu->gxpd);
>  		pm_runtime_put(gmu->dev);
>  		return ret;
>  	}
> @@ -919,19 +928,12 @@ int a6xx_gmu_resume(struct a6xx_gpu *a6xx_gpu)
>  	/* Set the GPU to the current freq */
>  	a6xx_gmu_set_initial_freq(gpu, gmu);
>  
> -	/*
> -	 * "enable" the GX power domain which won't actually do anything but it
> -	 * will make sure that the refcounting is correct in case we need to
> -	 * bring down the GX after a GMU failure
> -	 */
> -	if (!IS_ERR_OR_NULL(gmu->gxpd))
> -		pm_runtime_get(gmu->gxpd);
> -
>  out:
>  	/* On failure, shut down the GMU to leave it in a good state */
>  	if (ret) {
>  		disable_irq(gmu->gmu_irq);
>  		a6xx_rpmh_stop(gmu);
> +		pm_runtime_put(gmu->gxpd);
>  		pm_runtime_put(gmu->dev);
>  	}
>  
> -- 
> 2.7.4
> 

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