linux-kernel - Re: [Freedreno] [PATCH 5/6] drm: msm: a6xx: use dev_pm_opp_set_bw to set DDR bandwidth

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Date:   Thu, 28 May 2020 16:32:57 +0530
From:   Sharat Masetty <smasetty@...eaurora.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     freedreno <freedreno@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, dri-devel@...edesktop.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Georgi Djakov <georgi.djakov@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Viresh Kumar <viresh.kumar@...aro.org>, saravanak@...gle.com,
        Sibi Sankar <sibis@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Jordan Crouse <jcrouse@...eaurora.org>
Subject: Re: [Freedreno] [PATCH 5/6] drm: msm: a6xx: use dev_pm_opp_set_bw to
 set DDR bandwidth

On 5/27/2020 9:08 PM, Rob Clark wrote:
> On Wed, May 27, 2020 at 1:47 AM Sharat Masetty <smasetty@...eaurora.org> wrote:
>> + more folks
>>
>> On 5/18/2020 9:55 PM, Rob Clark wrote:
>>> On Mon, May 18, 2020 at 7:23 AM Jordan Crouse <jcrouse@...eaurora.org> wrote:
>>>> On Thu, May 14, 2020 at 04:24:18PM +0530, Sharat Masetty wrote:
>>>>> This patches replaces the previously used static DDR vote and uses
>>>>> dev_pm_opp_set_bw() to scale GPU->DDR bandwidth along with scaling
>>>>> GPU frequency.
>>>>>
>>>>> Signed-off-by: Sharat Masetty <smasetty@...eaurora.org>
>>>>> ---
>>>>>    drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 6 +-----
>>>>>    1 file changed, 1 insertion(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>>>>> index 2d8124b..79433d3 100644
>>>>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>>>>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>>>>> @@ -141,11 +141,7 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
>>>>>
>>>>>         gmu->freq = gmu->gpu_freqs[perf_index];
>>>>>
>>>>> -     /*
>>>>> -      * Eventually we will want to scale the path vote with the frequency but
>>>>> -      * for now leave it at max so that the performance is nominal.
>>>>> -      */
>>>>> -     icc_set_bw(gpu->icc_path, 0, MBps_to_icc(7216));
>>>>> +     dev_pm_opp_set_bw(&gpu->pdev->dev, opp);
>>>>>    }
>>>> This adds an implicit requirement that all targets need bandwidth settings
>>>> defined in the OPP or they won't get a bus vote at all. I would prefer that
>>>> there be an default escape valve but if not you'll need to add
>>>> bandwidth values for the sdm845 OPP that target doesn't regress.
>>>>
>>> it looks like we could maybe do something like:
>>>
>>>     ret = dev_pm_opp_set_bw(...);
>>>     if (ret) {
>>>         dev_warn_once(dev, "no bandwidth settings");
>>>         icc_set_bw(...);
>>>     }
>>>
>>> ?
>>>
>>> BR,
>>> -R
>> There is a bit of an issue here - Looks like its not possible to two icc
>> handles to the same path.  Its causing double enumeration of the paths
>> in the icc core and messing up path votes. With [1] Since opp/core
>> already gets a handle to the icc path as part of table add,  drm/msm
>> could do either
>>
>> a) Conditionally enumerate gpu->icc_path handle only when pm/opp core
>> has not got the icc path handle. I could use something like [2] to
>> determine if should initialize gpu->icc_path*
>>
>> b) Add peak-opp-configs in 845 dt and mandate all future versions to use
>> this bindings. With this, I can remove gpu->icc_path from msm/drm
>> completely and only rely on opp/core for bw voting.
> The main thing is that we want to make sure newer dtb always works on
> an older kernel without regression.. but, hmm..  I guess the
> interconnects/interconnects-names properties haven't landed yet in
> sdm845.dtsi?  Maybe that lets us go with the simpler approach (b).
> Looks like we haven't wired up interconnect for 8916 or 8996 either,
> so probably we can just mandate this for all of them?

I checked all three 845, 820 and 8916 and none of them have the 
interconnect configs for GPU. So, I think we are good here. I'll go with 
option (b) and re-spin v3. Adding interconnects and opp-peak-kBps 
configs for previous chips can be taken up as a separate activity.

Sharat

> If we have landed the interconnect dts hookup for gpu somewhere that
> I'm overlooking, I guess we would have to go with (a) and keep the
> existing interconnects/interconnects-names properties.
>
> BR,
> -R
>
>> [1] - https://lore.kernel.org/patchwork/cover/1240687/
>>
>> [2] - https://patchwork.kernel.org/patch/11527573/
>>
>> Let me know your thoughts
>>
>> Sharat
>>
>>>> Jordan
>>>>
>>>>>    unsigned long a6xx_gmu_get_freq(struct msm_gpu *gpu)
>>>>> --
>>>>> 2.7.4
>>>>>
>>>> --
>>>> The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>>>> a Linux Foundation Collaborative Project
>>>> _______________________________________________
>>>> Freedreno mailing list
>>>> Freedreno@...ts.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/freedreno

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