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

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Message-ID: <a936a9fc-6632-4f44-94d1-db304218b5a5@linaro.org>
Date: Mon, 25 Nov 2024 09:16:47 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Akhil P Oommen <quic_akhilpo@...cinc.com>
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 23/11/2024 20:43, Akhil P Oommen wrote:
> 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.

It depends on the bw table _and_ the a6xx_info.gmu table, I don't want to
check both in all parts on the driver.

Neil

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