linux-kernel - Re: [PATCH v2 4/4] drm/imagination: Skip clocks if platform PM manages resources

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Message-ID: <1226d261-247a-4a7c-a414-7db4a24fab9e@imgtec.com>
Date: Tue, 15 Apr 2025 09:15:23 +0000
From: Matt Coster <Matt.Coster@...tec.com>
To: Maxime Ripard <mripard@...nel.org>,
        Michal Wilczynski
	<m.wilczynski@...sung.com>
CC: "Rafael J. Wysocki" <rafael@...nel.org>,
        Danilo Krummrich
	<dakr@...nel.org>, Pavel Machek <pavel@...nel.org>,
        Drew Fustini
	<drew@...7.com>, Guo Ren <guoren@...nel.org>,
        Fu Wei <wefu@...hat.com>, Rob
 Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor
 Dooley <conor+dt@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Philipp
 Zabel <p.zabel@...gutronix.de>,
        Frank Binns <Frank.Binns@...tec.com>,
        Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann
	<tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter
	<simona@...ll.ch>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v2 4/4] drm/imagination: Skip clocks if platform PM
 manages resources

On 15/04/2025 09:55, Maxime Ripard wrote:
> On Mon, Apr 14, 2025 at 08:52:58PM +0200, Michal Wilczynski wrote:
>> Update the Imagination PVR driver to skip clock management during
>> initialization if the platform PM has indicated that it manages platform
>> resources.
>>
>> This is necessary for platforms like the T-HEAD TH1520, where the GPU's
>> clocks and resets are managed via a PM domain, and should not be
>> manipulated directly by the GPU driver.
>>
>> Signed-off-by: Michal Wilczynski <m.wilczynski@...sung.com>
>> ---
>>  drivers/gpu/drm/imagination/pvr_device.c | 14 ++++++++++----
>>  1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/imagination/pvr_device.c b/drivers/gpu/drm/imagination/pvr_device.c
>> index 1704c0268589bdeb65fa6535f9ec63182b0a3e94..f40468b99cf14da418aeecde086f009695ff877c 100644
>> --- a/drivers/gpu/drm/imagination/pvr_device.c
>> +++ b/drivers/gpu/drm/imagination/pvr_device.c
>> @@ -504,10 +504,16 @@ pvr_device_init(struct pvr_device *pvr_dev)
>>  	if (err)
>>  		return err;
>>  
>> -	/* Enable and initialize clocks required for the device to operate. */
>> -	err = pvr_device_clk_init(pvr_dev);
>> -	if (err)
>> -		return err;
>> +	/*
>> +	 * Only initialize clocks if they are not managed by the platform's
>> +	 * PM domain.
>> +	 */
>> +	if (!device_platform_resources_pm_managed(dev)) {
>> +		/* Enable and initialize clocks required for the device to operate. */
>> +		err = pvr_device_clk_init(pvr_dev);
>> +		if (err)
>> +			return err;
>> +	}
> 
> So, how does that work for devfreq? I can understand the rationale for
> resets and the sys clock, but the core clock at least should really be
> handled by the driver.

I agree, this feels a bit "all or nothing" to me. There's only one clock
on this platform that has issues, we can still control the other two
just fine.

I thought fixed clocks were the standard mechanism for exposing
non-controllable clocks to device drivers?

Cheers,
Matt

> 
> Maxime


-- 
Matt Coster
E: matt.coster@...tec.com


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