Re: [PATCH v4 4/9] drm/msm/dpu: make fix_core_ab_vote consistent with fix_core_ib_vote

[Dmitry Baryshkov]

On 11 January 2025 01:49:23 EET, Abhinav Kumar <quic_abhinavk at quicinc.com> wrote:
>
>
>On 1/9/2025 6:02 PM, Dmitry Baryshkov wrote:
>> On Thu, Jan 09, 2025 at 05:40:23PM -0800, Abhinav Kumar wrote:
>>> 
>>> 
>>> On 1/5/2025 7:07 PM, Dmitry Baryshkov wrote:
>>>> The fix_core_ab_vote is an average bandwidth value, used for bandwidth
>>>> overrides in several cases. However there is an internal inconsistency:
>>>> fix_core_ib_vote is defined in KBps, while fix_core_ab_vote is defined
>>>> in Bps.
>>>> 
>>>> Fix that by changing the type of the variable to u32 and using * 1000ULL
>>>> multiplier when setting up the dpu_core_perf_params::bw_ctl value.
>>>> 
>>> 
>>> Actually after looking at this, I have another question.
>>> 
>>> How did you conclude that fix_core_ib_vote is in KBps?
>>> 
>>> min_dram_ib is in KBps in the catalog but how is fix_core_ib_vote?
>>> 
>>> It depends on the interpretation perhaps. If the debugfs was supposed to
>>> operate under the expectation that the provided value will be pre-multiplied
>>> by 1000 and given then that explains why it was not multiplied again.
>>> 
>>> And I cross-checked some of the internal usages of the debugfs, the values
>>> provided to it were in Bps and not KBps.
>> 
>> Well... As you wrote min_dram_ib is in KBps. So, by comparing the next
>> two lines, fix_core_ib_vote should also be in kBps, as there is no
>> premultiplier:
>> 
>>                  perf->max_per_pipe_ib = core_perf->fix_core_ib_vote;
>> [...]
>>                  perf->max_per_pipe_ib = perf_cfg->min_dram_ib;
>> 
>> And then, as a proof, perf->max_per_pipe_ib is passed to icc_set_bw()
>> without any modifications:
>> 
>>                  icc_set_bw(kms->path[i], avg_bw, perf.max_per_pipe_ib);
>> 
>
>Understood max_per_pipe_ib. But then by the same logic, fix_core_ab_vote is always in Bps and not in KBps because bw_ctl is in Bps.
>
>Is it really a discrepancy that fix_core_ib_vote is defined in KBps, while fix_core_ab_vote is defined in Bps because they are just following the units in which bw_ctl and max_per_pipe_ib were defined in resp.

Yes. They come in pair, as a part of the user interface. If one is in Bps and another one in KBps, it is very easy to forget that and misinterpret them or to make a mistake while programming them. Not to mention that the threshold files, which are related to AB, are in KBps.

>
>> 
>>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
>>>> ---
>>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c | 4 ++--
>>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.h | 2 +-
>>>>    2 files changed, 3 insertions(+), 3 deletions(-)
>>>> 
>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
>>>> index 7263ab63a692554cd51a7fd91bd6250330179240..7cabc8f26908cfd2dbbffebd7c70fc37d9159733 100644
>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
>>>> @@ -125,7 +125,7 @@ static void _dpu_core_perf_calc_crtc(const struct dpu_core_perf *core_perf,
>>>>    		perf->max_per_pipe_ib = 0;
>>>>    		perf->core_clk_rate = 0;
>>>>    	} else if (core_perf->perf_tune.mode == DPU_PERF_MODE_FIXED) {
>>>> -		perf->bw_ctl = core_perf->fix_core_ab_vote;
>>>> +		perf->bw_ctl = core_perf->fix_core_ab_vote * 1000ULL;
>>>>    		perf->max_per_pipe_ib = core_perf->fix_core_ib_vote;
>>>>    		perf->core_clk_rate = core_perf->fix_core_clk_rate;
>>>>    	} else {
>>>> @@ -479,7 +479,7 @@ int dpu_core_perf_debugfs_init(struct dpu_kms *dpu_kms, struct dentry *parent)
>>>>    			&perf->fix_core_clk_rate);
>>>>    	debugfs_create_u32("fix_core_ib_vote", 0600, entry,
>>>>    			&perf->fix_core_ib_vote);
>>>> -	debugfs_create_u64("fix_core_ab_vote", 0600, entry,
>>>> +	debugfs_create_u32("fix_core_ab_vote", 0600, entry,
>>>>    			&perf->fix_core_ab_vote);
>>>>    	return 0;
>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.h
>>>> index ca4595b4ec217697849af02446b23ed0857a0295..5e07119c14c6a9ed3413d0eaddbd93df5cc3f79d 100644
>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.h
>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.h
>>>> @@ -51,7 +51,7 @@ struct dpu_core_perf {
>>>>    	u32 enable_bw_release;
>>>>    	u64 fix_core_clk_rate;
>>>>    	u32 fix_core_ib_vote;
>>>> -	u64 fix_core_ab_vote;
>>>> +	u32 fix_core_ab_vote;
>>>>    };
>>>>    int dpu_core_perf_crtc_check(struct drm_crtc *crtc,
>>>> 
>>