linux-kernel - Re: [PATCH v2 08/11] drm/msm: adreno: request for maximum bus bandwidth usage

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Message-ID: <79e76b0d-15df-444e-ab14-24cf32678b96@linaro.org>
Date: Wed, 27 Nov 2024 16:55:27 +0100
From: 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 08/11] drm/msm: adreno: request for maximum bus
 bandwidth usage

On 27/11/2024 16:46, Akhil P Oommen wrote:
> On 11/25/2024 1:44 PM, Neil Armstrong wrote:
>> On 23/11/2024 23:59, Akhil P Oommen wrote:
>>> On Tue, Nov 19, 2024 at 06:56:43PM +0100, Neil Armstrong wrote:
>>>> When requesting a DDR bandwidth level along a GPU frequency
>>>> level via the GMU, we can also specify the bus bandwidth usage in a
>>>> 16bit
>>>> quantitized value.
>>>>
>>>> For now simply request the maximum bus usage.
>>>
>>> Why? You don't care about power efficiency?
>>> Lets drop this patch. We don't care about AB vote yet.
>>
>> I care about functionality, without this AB vote the spillall use
>> case that fails on SM8650 HDK fails on the SM8650 QRD.
> 
> This should have been documented as a comment so that someone doesn't
> remove it in future.
> 
>>
>> AB is a quantitized value of the BW voted, so yes I expect we can have
>> 100% of the BW voted, but since we scale the BW it's perfectly fine.
> 
> Ah! no. MAX AB vote here is equal to the Max IB vote value in the hfi
> table. This is why I was asking about including all BW levels from the
> DT in the hfi table in the other patch.
> 
> So you are always voting for Max DDR Freq which is probably helping (or
> masking?) the spill all issue. We can just add a quirk to vote for MAX
> IB probably.

Oh, indeed I've been re-reading gen7_bus_ab_quantize() and it seems
I should calculate the AB vote when building the bw_table.

Thanks,
Neil

> 
> -Akhil
> 
>>
>> Neil
>>
>>>
>>> -Akhil
>>>
>>>>
>>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>>>> ---
>>>>    drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 11 +++++++++++
>>>>    drivers/gpu/drm/msm/adreno/a6xx_hfi.h |  5 +++++
>>>>    2 files changed, 16 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/
>>>> msm/adreno/a6xx_gmu.c
>>>> index
>>>> dc2d0035544e7848e5c4ea27f1ea9a191f9c4991..36c0f67fd8e109aabf09a0804bacbed3593c39d7 100644
>>>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>>>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>>>> @@ -134,6 +134,17 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu,
>>>> struct dev_pm_opp *opp,
>>>>                if (bw == gmu->gpu_bw_table[bw_index])
>>>>                    break;
>>>>            }
>>>> +
>>>> +        if (bw_index) {
>>>> +            /*
>>>> +             * Append AB vote to the maximum bus usage.
>>>> +             * AB represents a quantitized 16bit value of the
>>>> +             * max ddr bandwidth we could use, let's simply
>>>> +             * request the maximum for now.
>>>> +             */
>>>> +            bw_index |= AB_VOTE(MAX_AB_VOTE);
>>>> +            bw_index |= AB_VOTE_ENABLE;
>>>> +        }
>>>>        }
>>>>          gmu->current_perf_index = perf_index;
>>>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_hfi.h b/drivers/gpu/drm/
>>>> msm/adreno/a6xx_hfi.h
>>>> index
>>>> 528110169398f69f16443a29a1594d19c36fb595..52ba4a07d7b9a709289acd244a751ace9bdaab5d 100644
>>>> --- a/drivers/gpu/drm/msm/adreno/a6xx_hfi.h
>>>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_hfi.h
>>>> @@ -173,6 +173,11 @@ struct a6xx_hfi_gx_bw_perf_vote_cmd {
>>>>        u32 bw;
>>>>    };
>>>>    +#define AB_VOTE_MASK        GENMASK(31, 16)
>>>> +#define MAX_AB_VOTE        (FIELD_MAX(AB_VOTE_MASK) - 1)
>>>> +#define AB_VOTE(vote)        FIELD_PREP(AB_VOTE_MASK, (vote))
>>>> +#define AB_VOTE_ENABLE        BIT(8)
>>>> +
>>>>    #define HFI_H2F_MSG_PREPARE_SLUMBER 33
>>>>      struct a6xx_hfi_prep_slumber_cmd {
>>>>
>>>> -- 
>>>> 2.34.1
>>>>
>>
>