Re: [PATCH v5 2/7] drm/msm: adreno: add plumbing to generate bandwidth vote table for GMU

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

On 12/12/2024 20:55, Konrad Dybcio wrote:
> On 11.12.2024 9:29 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 other side 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 vote will be calculated later when setting the frequency.
>>
>> The vote array will then be used to dynamically generate the GMU
>> bw_table sent during the GMU power-up.
>>
>> 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 | 144 ++++++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/msm/adreno/a6xx_gmu.h |  13 +++
>>   drivers/gpu/drm/msm/adreno/a6xx_gpu.h |   1 +
>>   3 files changed, 158 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>> index 14db7376c712d19446b38152e480bd5a1e0a5198..36696d372a42a27b26a018b19e73bc6d8a4a5235 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 +1288,101 @@ 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;
>> +};
> 
> No. This is a direct copypasta of drivers/interconnect/qcom/icc-rpmh.h
> You cannot just randomly duplicate things..
> 
> Move it out to a shared header in include/ (and remove the duplicate from
> clk-rpmh.c while at it)
> 

Not sure if this a good idea

> 
> I'd also really prefer if you took
> 
> drivers/interconnect/qcom/bcm-voter.c : tcs_list_gen()
> 
> and abstracted it to operate on struct bcm_db with any additional
> required parameters passed as arguments.. Still left some comments
> on this version if you decide to go with it

They are still very different, look closely, tcs_list_gen is designed to
operate on BW aggregations + scsaling, it would make no sense to unify them.

The calculation is simple enough, I made it explicitely easy to read and
maintain, but honestly there's nothing special.

> 
>> +
>> +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;
> 
> You already checked that from the caller

Good catch

> 
>> +
>> +	/* 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;
> 
> Unconfigured doesn't really fit here.. Maybe just mention the list is NULL
> -terminated

Ack

> 
>> +
>> +		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;
> 
> If this condition ever happens, it'll be impossible to track down,
> please add an err message

Hmm sure

> 
>> +
>> +		++bcm_count;
> 
> I've heard somewhere that prefixed increments are discouraged for
> "reasons" and my OCD would like to support that

Never got this memo...

> 
>> +	}
>> +
>> +	/* 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() */
>> +		for (bcm_index = 0; bcm_index < bcm_count; bcm_index++) {
>> +			bool commit = false;
>> +			u64 peak;
>> +			u32 vote;
>> +
>> +			/* Skip unconfigured BCM */
>> +			if (!bcm_data[bcm_index])
>> +				continue;
> 
> I don't see how this is useful here

It's a leftover, will drop

> 
>> +
>> +			if (bcm_index == bcm_count - 1 ||
>> +			    (bcm_data[bcm_index + 1] &&
>> +			     bcm_data[bcm_index]->vcd != bcm_data[bcm_index + 1]->vcd))
>> +				commit = true;
>> +
>> +			if (!bw) {
>> +				data[bcm_index] = BCM_TCS_CMD(commit, false, 0, 0);
>> +				continue;
>> +			}
>> +
>> +			if (info->bcms[bcm_index].fixed) {
> 
> You may want to take a pointer to info->bcms[bcm_index]

Sure, will help

> 
>> +				u32 perfmode = 0;
>> +
>> +				if (bw >= info->bcms[bcm_index].perfmode_bw)
>> +					perfmode = info->bcms[bcm_index].perfmode;
>> +
>> +				data[bcm_index] = BCM_TCS_CMD(commit, true, 0, perfmode);
>> +				continue;
>> +			}
>> +
>> +			/* Multiply the bandwidth by the width of the connection */
>> +			peak = (u64)bw * le16_to_cpu(bcm_data[bcm_index]->width);
>> +			do_div(peak, info->bcms[bcm_index].buswidth);
>> +
>> +			/* Input bandwidth value is in KBps, scale the value to BCM unit */
>> +			peak *= 1000ULL;
> 
> I don't think this needs to be ULL since the other argument is an u64
> 
>> +			do_div(peak, le32_to_cpu(bcm_data[bcm_index]->unit));
>> +
>> +			vote = clamp(peak, 1, BCM_TCS_CMD_VOTE_MASK);
>> +
>> +			data[bcm_index] = BCM_TCS_CMD(commit, true, vote, vote);
> 
> x is the avg vote, y is the peak vote

downstream sets both calculated from the exact same value and the same way...

> 
> Just noting down for my future self I guess, a6xx sets ab=0,
> a7xx sets ab=ib like you did here

Probably, I'll need to check on that, but it can be done in a second step when enabling it on a6xx

> 
> Konrad