linux-kernel - Re: [PATCH 11/17] drm/msm: Add support for IFPC

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Message-ID: <5471754b-5dec-4107-96d6-a6075328d824@oss.qualcomm.com>
Date: Wed, 23 Jul 2025 12:27:25 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Akhil P Oommen <akhilpo@....qualcomm.com>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/17] drm/msm: Add support for IFPC

On 7/22/25 11:27 PM, Akhil P Oommen wrote:
> On 7/22/2025 7:19 PM, Dmitry Baryshkov wrote:
>> On Sun, Jul 20, 2025 at 05:46:12PM +0530, Akhil P Oommen wrote:
>>> Add a new quirk to denote IFPC (Inter-Frame Power Collapse) support
>>> for a gpu. Based on this flag send the feature ctrl hfi message to
>>> GMU to enable IFPC support.
>>>
>>> Signed-off-by: Akhil P Oommen <akhilpo@....qualcomm.com>
>>> ---

[...]

>>> +static int a6xx_hfi_enable_ifpc(struct a6xx_gmu *gmu)
>>> +{
>>> +	if (gmu->idle_level != GMU_IDLE_STATE_IFPC)
>>> +		return 0;
>>> +
>>> +	return a6xx_hfi_feature_ctrl_msg(gmu, HFI_FEATURE_IFPC, 1, 0x1680);
>>
>> magic number?
>>
> 
> Let me check.

techpack-graphics/adreno_a6xx_gmu.c:
537:#define A6X_GMU_LONG_IFPC_HYST      FIELD_PREP(GENMASK(15, 0), 0x1680)
541:#define A6X_GMU_LONG_IFPC_HYST_FLOOR        FIELD_PREP(GENMASK(15, 0), 0x0F00)

(same value for a7/a8)

0x0f00 is 3840, which smells oddly like the XO clock rate (possibly mul/div2)

(38.4 MHz or 19.2) / 3840 is (1000 or 500) (ms? us? cycles?) and the other one is
(333 or 667) - without any further information I'd estimate this is some sort of
scheduler tuning

Konrad