linux-kernel - Re: [PATCH] ALSA: hda/tegra: enable clock during probe

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Message-ID: <da021878-5d89-c6d3-e5b2-4ab20f9b573b@nvidia.com>
Date:   Mon, 28 Jan 2019 11:36:58 +0530
From:   Sameer Pujar <spujar@...dia.com>
To:     Jon Hunter <jonathanh@...dia.com>, Takashi Iwai <tiwai@...e.de>
CC:     <pierre-louis.bossart@...ux.intel.com>, <perex@...ex.cz>,
        <alsa-devel@...a-project.org>, <thierry.reding@...il.com>,
        <rlokhande@...dia.com>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] ALSA: hda/tegra: enable clock during probe


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@...dia.com>
>>>>>>> Reviewed-by: Ravindra Lokhande <rlokhande@...dia.com>
>>>>>>> Reviewed-by: Jon Hunter <jonathanh@...dia.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
>