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

[Krzysztof Kozlowski <krzk@kernel.org>]

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