Message-ID: <4aee601a-f72c-7c94-60cb-ec2546900b8c@nvidia.com>
Date:   Wed, 30 Jan 2019 16:26:31 +0530
From:   Sameer Pujar <spujar@...dia.com>
To:     Takashi Iwai <tiwai@...e.de>, Jon Hunter <jonathanh@...dia.com>
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 1/30/2019 4:09 PM, Takashi Iwai wrote:
> On Wed, 30 Jan 2019 10:35:35 +0100,
> Jon Hunter wrote:
>>
>> 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.
> Only from my personal taste, I find the v2 patch is better.
> It like simpler, after all.  That is, the code in v1 patch
>
> 	probe() {
> 		....
> 		pm_runtime_enable();
> 		....
> 		if (!pm_runtime_enabled())
> 			hda_tegra_runtime_resume();
> 		schedule_work();
> 	}
>
> 	work() {
> 		pm_runtime_get_sync();
> 		....
> 		pm_runtime_put();
> 	}
>
> becomes shorter in v2:
>
> 	probe() {
> 		....
> 		hda_tegra_enable_clocks();
> 		schedule_work();
> 	}
>
> 	work() {
> 		....
> 		pm_runtime_enable();
> 	}
>
>
> However, the point about hda_tegra_remove() you raised in the v2 patch
> is still valid.  (BTW, I guess the discussion followed in that thread
> was somehow misunderstood; your argument was about hda_tegra_remove()
> while Sameer discussed about the probe.)  It can be with
> hda_tegra_disable_clocks() if we want more consistency.
>
> Though, I don't mind too much about that as long as the proper comment
> is given.
We might need entire functionality of hda_tegra_runtime_suspend() 
replicated here,
if hda_tegra_disable_clocks() were to be used. Right now it takes care 
of both the
cases where runtime PM is enabled/disabled. If you all agree, we can 
move the
discussion to v2 patch.

Thanks,
Sameer.
>
> thanks,
>
> Takashi

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