linux-kernel - Re: [PATCH v3 2/7] drm/msm: adreno: add plumbing to generate bandwidth vote table for GMU

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Message-ID: <df17e3c8-7096-4b22-b85e-bff4bbdee3b2@linaro.org>
Date: Mon, 2 Dec 2024 09:41:06 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 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>, Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH v3 2/7] drm/msm: adreno: add plumbing to generate
 bandwidth vote table for GMU

On 29/11/2024 16:21, Konrad Dybcio wrote:
> On 28.11.2024 11:25 AM, Neil Armstrong wrote:
>> The Adreno GPU Management Unit (GMU) can also scale DDR Bandwidth along
>> the Frequency and Power Domain level, but by default we leave the
>> OPP core scale 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.
>>
>> In order to calculate vote values used by the GPU Management
>> Unit (GMU), we need to parse all the possible OPP Bandwidths and
>> create a vote value to be sent to the appropriate Bus Control
>> Modules (BCMs) declared in the GPU info struct.
>>
>> This vote value is called IB, while on the othe side the GMU also
>> takes another vote called AB which is a 16bit quantized value
>> of the bandwidth against the maximum supported bandwidth.
>>
>> The vote array will then be used to dynamically generate the GMU
>> bw_table sent during the GMU power-up.
>>
>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>> ---
>>   drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 174 ++++++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/msm/adreno/a6xx_gmu.h |  14 +++
>>   drivers/gpu/drm/msm/adreno/a6xx_gpu.h |   1 +
>>   drivers/gpu/drm/msm/adreno/a6xx_hfi.h |   5 +
>>   4 files changed, 194 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>> index 14db7376c712d19446b38152e480bd5a1e0a5198..ee2010a01186721dd377f1655fcf05ddaff77131 100644
>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>> @@ -9,6 +9,7 @@
>>   #include <linux/pm_domain.h>
>>   #include <linux/pm_opp.h>
>>   #include <soc/qcom/cmd-db.h>
>> +#include <soc/qcom/tcs.h>
>>   #include <drm/drm_gem.h>
>>   
>>   #include "a6xx_gpu.h"
>> @@ -1287,6 +1288,131 @@ static int a6xx_gmu_memory_probe(struct a6xx_gmu *gmu)
>>   	return 0;
>>   }
>>   
>> +/**
>> + * struct bcm_db - Auxiliary data pertaining to each Bus Clock Manager (BCM)
>> + * @unit: divisor used to convert bytes/sec bw value to an RPMh msg
>> + * @width: multiplier used to convert bytes/sec bw value to an RPMh msg
>> + * @vcd: virtual clock domain that this bcm belongs to
>> + * @reserved: reserved field
>> + */
>> +struct bcm_db {
>> +	__le32 unit;
>> +	__le16 width;
>> +	u8 vcd;
>> +	u8 reserved;
>> +};
>> +
>> +static u64 bcm_div(u64 num, u32 base)
>> +{
>> +	/* Ensure that small votes aren't lost. */
>> +	if (num && num < base)
>> +		return 1;
>> +
>> +	do_div(num, base);
>> +
>> +	return num;
>> +}
> 
> This should live in include/soc/qcom/bcm.h, similarly to tcs.h in
> that directory

Honestly, I don't think so, there's no bcm specific logic here, we
simply avoid returning 0 after a division

> 
>> +static int a6xx_gmu_rpmh_bw_votes_init(const struct a6xx_info *info,
>> +				       struct a6xx_gmu *gmu)
>> +{
>> +	const struct bcm_db *bcm_data[GMU_MAX_BCMS] = { 0 };
>> +	unsigned int bcm_index, bw_index, bcm_count = 0;
>> +
>> +	if (!info->bcms)
>> +		return 0;
>> +
>> +	/* Retrieve BCM data from cmd-db */
>> +	for (bcm_index = 0; bcm_index < GMU_MAX_BCMS; bcm_index++) {
>> +		size_t count;
>> +
>> +		/* Stop at first unconfigured bcm */
>> +		if (!info->bcms[bcm_index].name)
>> +			break;
>> +
>> +		bcm_data[bcm_index] = cmd_db_read_aux_data(
>> +						info->bcms[bcm_index].name,
>> +						&count);
>> +		if (IS_ERR(bcm_data[bcm_index]))
>> +			return PTR_ERR(bcm_data[bcm_index]);
>> +
>> +		if (!count)
>> +			return -EINVAL;
>> +
>> +		++bcm_count;
>> +	}
>> +
>> +	/* Generate BCM votes values for each bandwidth & BCM */
>> +	for (bw_index = 0; bw_index < gmu->nr_gpu_bws; bw_index++) {
>> +		u32 *data = gmu->gpu_ib_votes[bw_index];
>> +		u32 bw = gmu->gpu_bw_table[bw_index];
>> +
>> +		/* Calculations loosely copied from bcm_aggregate() & tcs_cmd_gen() */
> 
> Ditto, perhaps this should be exported from icc

I think it's a bad idea to share code because the overall structures and purposes
are completely different, and it will make the gpu maintenance a nightmare.

> 
> [...]
> 
> Konrad

Thanks,
Neil