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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

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)


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

> +
> +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

> +
> +	/* 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

> +
> +		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

> +
> +		++bcm_count;

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

> +	}
> +
> +	/* 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

> +
> +			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]

> +				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

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

Konrad