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SubjectRe: [PATCH] ALSA: hda/tegra: enable clock during probe
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On 1/25/2019 7:34 PM, Jon Hunter wrote:
> On 25/01/2019 13:58, Takashi Iwai wrote:
>> On Fri, 25 Jan 2019 14:26:27 +0100,
>> Jon Hunter wrote:
>>>
>>> On 25/01/2019 12:40, Takashi Iwai wrote:
>>>> On Fri, 25 Jan 2019 12:36:00 +0100,
>>>> Jon Hunter wrote:
>>>>>
>>>>> On 24/01/2019 19:08, Takashi Iwai wrote:
>>>>>> On Thu, 24 Jan 2019 18:36:43 +0100,
>>>>>> Sameer Pujar wrote:
>>>>>>> If CONFIG_PM is disabled or runtime PM calls are forbidden, the clocks
>>>>>>> will not be ON. This could cause issue during probe, where hda init
>>>>>>> setup is done. This patch checks whether runtime PM is enabled or not.
>>>>>>> If disabled, clocks are enabled in probe() and disabled in remove()
>>>>>>>
>>>>>>> This patch does following minor changes as cleanup,
>>>>>>> * return code check for pm_runtime_get_sync() to take care of failure
>>>>>>> and exit gracefully.
>>>>>>> * In remove path runtime PM is disabled before calling snd_card_free().
>>>>>>> * hda_tegra_disable_clocks() is moved out of CONFIG_PM_SLEEP check.
>>>>>>> * runtime PM callbacks moved out of CONFIG_PM check
>>>>>>>
>>>>>>> Signed-off-by: Sameer Pujar <spujar@nvidia.com>
>>>>>>> Reviewed-by: Ravindra Lokhande <rlokhande@nvidia.com>
>>>>>>> Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
>>>>>> (snip)
>>>>>>> @@ -555,6 +553,13 @@ static int hda_tegra_probe(struct platform_device *pdev)
>>>>>>> if (!azx_has_pm_runtime(chip))
>>>>>>> pm_runtime_forbid(hda->dev);
>>>>>>>
>>>>>>> + /* explicit resume if runtime PM is disabled */
>>>>>>> + if (!pm_runtime_enabled(hda->dev)) {
>>>>>>> + err = hda_tegra_runtime_resume(hda->dev);
>>>>>>> + if (err)
>>>>>>> + goto out_free;
>>>>>>> + }
>>>>>>> +
>>>>>>> schedule_work(&hda->probe_work);
>>>>>> Calling runtime_resume here is really confusing...
>>>>> Why? IMO it is better to have a single handler for resuming the device
>>>>> and so if RPM is not enabled we call the handler directly. This is what
>>>>> we have been advised to do in the past and do in other drivers. See ...
>>>> The point is that we're not "resuming" anything there. It's in the
>>>> early probe stage, and the device state is uninitialized, not really
>>>> suspended. It'd end up with just calling the same helper
>>>> (hda_tegra_enable_clocks()), though.
>>> Yes and you can make the same argument for every driver that calls
>>> pm_runtime_get_sync() during probe to turn on clocks, handle resets,
>>> etc, because at the end of the day the very first call to
>>> pm_runtime_get_sync() invokes the runtime_resume callback, when we have
>>> never been suspended.
>> Although there are some magical pm_runtime_*() in some places, most of
>> such pm_runtime_get_sync() is for the actual runtime PM management (to
>> prevent the runtime suspend), while the code above is for explicitly
>> setting up something for non-PM cases.
>>
>> And if pm_runtime_get_sync() is obviously superfluous, we should
>> remove such calls. Really.
> Yes agree.
>
>>> Yes at the end of the day it is the same and given that we have done
>>> this elsewhere I think it is good to be consistent if/where we can.
>> The code becomes less readable, and that's a good reason against it :)
> I don't its less readable. However, I do think it is less error prone :-)

Do we have a consensus here? Request others to provide opinions to help
close on this.

Thanks,
Sameer.

> Jon
>

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