linux-kernel - Re: [PATCH v3 3/8] drm/imagination: Use pwrseq for TH1520 GPU power management

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Message-ID: <e5a0bee2-ff74-47cf-ad2c-0c78b57ae6cf@kernel.org>
Date: Wed, 4 Jun 2025 08:36:10 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Michal Wilczynski <m.wilczynski@...sung.com>
Cc: 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>, Bartosz Golaszewski <brgl@...ev.pl>,
 Philipp Zabel <p.zabel@...gutronix.de>, Frank Binns
 <frank.binns@...tec.com>, Matt Coster <matt.coster@...tec.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>, Ulf Hansson <ulf.hansson@...aro.org>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 3/8] drm/imagination: Use pwrseq for TH1520 GPU power
 management

On 03/06/2025 21:43, Michal Wilczynski wrote:
>>> +	 * and resets. Otherwise, we fall back to managing them ourselves.
>>> +	 */
>>> +	pvr_dev->pwrseq = devm_pwrseq_get(dev, "gpu-power");
>>> +	if (IS_ERR(pvr_dev->pwrseq)) {
>>> +		int pwrseq_err = PTR_ERR(pvr_dev->pwrseq);
>>> +
>>> +		/*
>>> +		 * If the error is -EPROBE_DEFER, it's because the
>>> +		 * optional sequencer provider is not present
>>> +		 * and it's safe to fall back on manual power-up.
>>
>> It is safe but why it is desirable? The rule is rather to defer the
>> probe, assuming this is probe path.
> 
> Yeah this is probe path.
> 
> The GPU node will depend on the AON node, which will be the sole
> provider for the 'gpu-power' sequencer (based on the discussion in patch
> 1).
> 
> Therefore, if the AON/pwrseq driver has already completed its probe, and
> devm_pwrseq_get() in the GPU driver subsequently returns -EPROBE_DEFER
> (because pwrseq_get found 'no match' on the bus for 'gpu-power'), the
> interpretation is that the AON driver did not register this optional
> sequencer. Since AON is the only anticipated source, it implies the
> sequencer won't become available later from its designated provider.

I don't understand why you made this assumption. AON could be a module
and this driver built-in. AON will likely probe later.



Best regards,
Krzysztof