linux-kernel - Re: [PATCH v2 04/11] drm/msm: adreno: add GMU_BW

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Message-ID: <20241123194316.yqvovktcptfep4dr@hu-akhilpo-hyd.qualcomm.com>
Date: Sun, 24 Nov 2024 01:13:16 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: Neil Armstrong <neil.armstrong@...aro.org>
CC: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        "Stephen
 Boyd" <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Clark
	<robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio
	<konradybcio@...nel.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        "Dmitry
 Baryshkov" <dmitry.baryshkov@...aro.org>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Simona
 Vetter" <simona@...ll.ch>,
        Bjorn Andersson <andersson@...nel.org>, Rob
 Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor
 Dooley <conor+dt@...nel.org>,
        Connor Abbott <cwabbott0@...il.com>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <freedreno@...ts.freedesktop.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 04/11] drm/msm: adreno: add GMU_BW_VOTE feature flag

On Tue, Nov 19, 2024 at 06:56:39PM +0100, Neil Armstrong wrote:
> The Adreno GMU Management Unit (GNU) can also scale the DDR Bandwidth
> along the Frequency and Power Domain level, but by default we leave the
> OPP core vote for the interconnect ddr path.
> 
> While scaling via the interconnect path was sufficient, newer GPUs
> like the A750 requires specific vote paremeters and bandwidth to
> achieve full functionality.
> 
> While the feature will require some data in a6xx_info, it's safer
> to only enable tested platforms with this flag first.
> 
> Add a new feature enabling DDR Bandwidth vote via GMU.
> 
> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> ---
>  drivers/gpu/drm/msm/adreno/adreno_gpu.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.h b/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> index 4702d4cfca3b58fb3cbb25cb6805f1c19be2ebcb..394b96eb6c83354ae008b15b562bedb96cd391dd 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> @@ -58,6 +58,7 @@ enum adreno_family {
>  #define ADRENO_FEAT_HAS_HW_APRIV		BIT(0)
>  #define ADRENO_FEAT_HAS_CACHED_COHERENT		BIT(1)
>  #define ADRENO_FEAT_PREEMPTION			BIT(2)
> +#define ADRENO_FEAT_GMU_BW_VOTE			BIT(3)

Do we really need a feature flag for this? We have to carry this for every
GPU going forward. IB voting is supported on all GMUs from A6xx GEN2 and
newer. So we can just check that along with whether the bw table is
dynamically generated or not.

-Akhil

>  
>  /* Helper for formating the chip_id in the way that userspace tools like
>   * crashdec expect.
> 
> -- 
> 2.34.1
>