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Date:   Tue, 6 Jun 2023 22:48:24 +0530
From:   Akhil P Oommen <quic_akhilpo@quicinc.com>
To:     Konrad Dybcio <konrad.dybcio@linaro.org>
CC:     Rob Clark <robdclark@gmail.com>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Conor Dooley <conor+dt@kernel.org>,
        <linux-arm-msm@vger.kernel.org>, <dri-devel@lists.freedesktop.org>,
        <freedreno@lists.freedesktop.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Rob Clark <robdclark@chromium.org>,
        Marijn Suijten <marijn.suijten@somainline.org>
Subject: Re: [PATCH v8 07/18] drm/msm/a6xx: Add a helper for
 software-resetting the GPU
Message-ID: <jplt5g5xuphbnci73pdtaxd63fguxtgtp4c37kc7ehavzrjbau@kamshezxnvgy>
References: <20230223-topic-gmuwrapper-v8-0-69c68206609e@linaro.org>
 <20230223-topic-gmuwrapper-v8-7-69c68206609e@linaro.org>
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In-Reply-To: <20230223-topic-gmuwrapper-v8-7-69c68206609e@linaro.org>
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On Mon, May 29, 2023 at 03:52:26PM +0200, Konrad Dybcio wrote:
> 
> Introduce a6xx_gpu_sw_reset() in preparation for adding GMU wrapper
> GPUs and reuse it in a6xx_gmu_force_off().
> 
> This helper, contrary to the original usage in GMU code paths, adds
> a write memory barrier which together with the necessary delay should
> ensure that the reset is never deasserted too quickly due to e.g. OoO
> execution going crazy.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.c |  3 +--
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 11 +++++++++++
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.h |  1 +
>  3 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> index b86be123ecd0..5ba8cba69383 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> @@ -899,8 +899,7 @@ static void a6xx_gmu_force_off(struct a6xx_gmu *gmu)
>  	a6xx_bus_clear_pending_transactions(adreno_gpu, true);
>  
>  	/* Reset GPU core blocks */
> -	gpu_write(gpu, REG_A6XX_RBBM_SW_RESET_CMD, 1);
> -	udelay(100);
> +	a6xx_gpu_sw_reset(gpu, true);
>  }
>  
>  static void a6xx_gmu_set_initial_freq(struct msm_gpu *gpu, struct a6xx_gmu *gmu)
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index e3ac3f045665..083ccb5bcb4e 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -1634,6 +1634,17 @@ void a6xx_bus_clear_pending_transactions(struct adreno_gpu *adreno_gpu, bool gx_
>  	gpu_write(gpu, REG_A6XX_GBIF_HALT, 0x0);
>  }
>  
> +void a6xx_gpu_sw_reset(struct msm_gpu *gpu, bool assert)
> +{
> +	gpu_write(gpu, REG_A6XX_RBBM_SW_RESET_CMD, assert);
> +	/* Add a barrier to avoid bad surprises */
Can you please make this comment a bit more clear? Highlight that we
should ensure the register is posted at hw before polling.

I think this barrier is required only during assert.

-Akhil.
> +	mb();
> +
> +	/* The reset line needs to be asserted for at least 100 us */
> +	if (assert)
> +		udelay(100);
> +}
> +
>  static int a6xx_pm_resume(struct msm_gpu *gpu)
>  {
>  	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> index 9580def06d45..aa70390ee1c6 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> @@ -89,5 +89,6 @@ struct msm_gpu_state *a6xx_gpu_state_get(struct msm_gpu *gpu);
>  int a6xx_gpu_state_put(struct msm_gpu_state *state);
>  
>  void a6xx_bus_clear_pending_transactions(struct adreno_gpu *adreno_gpu, bool gx_off);
> +void a6xx_gpu_sw_reset(struct msm_gpu *gpu, bool assert);
>  
>  #endif /* __A6XX_GPU_H__ */
> 
> -- 
> 2.40.1
>