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

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Message-ID: <ef05ac7a-8fa8-5776-312a-afecdeae10c6@nvidia.com>
Date:   Wed, 30 Jan 2019 09:35:35 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Sameer Pujar <spujar@...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 28/01/2019 06:06, Sameer Pujar wrote:
> 
> 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.

I am not going to block this and ultimately it is Iwai-san call.

However, I wonder if it would be appropriate to move the whole ...

 if (pm_runtime_enabled())
         ret = pm_runtime_get_sync();
 else
         ret = hda_tegra_runtime_resume();

... into the probe_work function? In other words, we are just resuming
when we really need to. Unless I am still misunderstanding Iwai-san
comment. Otherwise if Iwai-san is happy with V2 then go with that.

Cheers
Jon
-- 
nvpublic