Re: [PATCH v5 4/7] drm/msm: adreno: find bandwidth index of OPP and set it along freq index

[Neil Armstrong <neil.armstrong@linaro.org>]

On 12/12/2024 21:21, Konrad Dybcio wrote:
> On 11.12.2024 9:29 AM, Neil Armstrong wrote:
>> The Adreno GPU Management Unit (GMU) can also scale the DDR Bandwidth
>> along the Frequency and Power Domain level, until now we left the OPP
>> core scale the OPP bandwidth via the interconnect path.
>>
>> In order to enable bandwidth voting via the GPU Management
>> Unit (GMU), when an opp is set by devfreq we also look for
>> the corresponding bandwidth index in the previously generated
>> bw_table and pass this value along the frequency index to the GMU.
>>
>> The GMU also takes another vote called AB which is a 16bit quantized
>> value of the floor bandwidth against the maximum supported bandwidth.
>>
>> The AB is calculated with a default 25% of the bandwidth like the
>> downstream implementation too inform the GMU firmware the minimal
>> quantity of bandwidth we require for this OPP.
>>
>> Since we now vote for all resources via the GMU, setting the OPP
>> is no more needed, so we can completely skip calling
>> dev_pm_opp_set_opp() in this situation.
>>
>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>> Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
>> Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
>> ---
>>   drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 39 +++++++++++++++++++++++++++++++++--
>>   drivers/gpu/drm/msm/adreno/a6xx_gmu.h |  2 +-
>>   drivers/gpu/drm/msm/adreno/a6xx_hfi.c |  6 +++---
>>   drivers/gpu/drm/msm/adreno/a6xx_hfi.h |  5 +++++
>>   4 files changed, 46 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>> index 36696d372a42a27b26a018b19e73bc6d8a4a5235..46ae0ec7a16a41d55755ce04fb32404cdba087be 100644
>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>> @@ -110,9 +110,11 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp,
>>   		       bool suspended)
>>   {
>>   	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>> +	const struct a6xx_info *info = adreno_gpu->info->a6xx;
>>   	struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
>>   	struct a6xx_gmu *gmu = &a6xx_gpu->gmu;
>>   	u32 perf_index;
>> +	u32 bw_index = 0;
>>   	unsigned long gpu_freq;
>>   	int ret = 0;
>>   
>> @@ -125,6 +127,37 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp,
>>   		if (gpu_freq == gmu->gpu_freqs[perf_index])
>>   			break;
>>   
>> +	/* If enabled, find the corresponding DDR bandwidth index */
>> +	if (info->bcms && gmu->nr_gpu_bws > 1) {
> 
> if (gmu->nr_gpu_bws)

gmu->nr_gpu_bws == 1 means there's not BW in the OPPs (index 0 is the "off" state)

> 
>> +		unsigned int bw = dev_pm_opp_get_bw(opp, true, 0);
>> +
>> +		for (bw_index = 0; bw_index < gmu->nr_gpu_bws - 1; bw_index++) {
>> +			if (bw == gmu->gpu_bw_table[bw_index])
>> +				break;
>> +		}
>> +
>> +		/* Vote AB as a fraction of the max bandwidth */
>> +		if (bw) {
> 
> This seems to only be introduced with certain a7xx too.. you should
> ping the GMU with HFI_VALUE_GMU_AB_VOTE to check if it's supported

Good point

> 
>> +			u64 tmp;
>> +
>> +			/* For now, vote for 25% of the bandwidth */
>> +			tmp = bw * 25;
>> +			do_div(tmp, 100);
>> +
>> +			/*
>> +			 * The AB vote consists of a 16 bit wide quantized level
>> +			 * against the maximum supported bandwidth.
>> +			 * Quantization can be calculated as below:
>> +			 * vote = (bandwidth * 2^16) / max bandwidth
>> +			 */
>> +			tmp *= MAX_AB_VOTE;
>> +			do_div(tmp, gmu->gpu_bw_table[gmu->nr_gpu_bws - 1]);
>> +
>> +			bw_index |= AB_VOTE(clamp(tmp, 1, MAX_AB_VOTE));
>> +			bw_index |= AB_VOTE_ENABLE;
>> +		}
>> +	}
> 
> BTW, did you dump the values we send to the GMU here and in the RPMh
> builder part & validate against downstream?

It matches how downstream builds the Ab vote yes

> 
> Konrad