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

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Date:   Fri, 25 Jan 2019 14:04:56 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Takashi Iwai <tiwai@...e.de>
CC:     Sameer Pujar <spujar@...dia.com>,
        <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 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 :-)

Jon

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