linux-kernel - Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer

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Date:   Mon, 4 Sep 2017 21:45:32 +0900
From:   Takashi Sakamoto <o-takashi@...amocchi.jp>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     alsa-devel@...a-project.org, keescook@...omium.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, john.stultz@...aro.org, tglx@...utronix.de,
        hch@....org, anna-maria@...utronix.de
Subject: Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer

Hi,

On Sep 2 2017 10:19, Takashi Sakamoto wrote:
> Well, in sound subsystem, there're a few drivers which uses hrtimer:
>   - snd-pcsp
>   - snd-sh-dac-audio
>   - snd-soc-imx-pcm-fiq
> 
> As a quick glance, 'snd-sh-dac-audio' includes the same bug, too. 
> Additionally, 'snd-soc-imx-pcm-fiq' maintains hrtimer with loose manner 
> in a point of state of PCM substream and it shall gain the same bug if 
> improved. Later, I posted some patches for them.

After reading code thoroughly, I conclude that no need to fix these two
drivers. They're programmed with own protections. The former
(snd-sh-dac-audio) has 'struct snd_sh_dac.empty' and the latter
(snd-soc-imx-pcm-fiq) has 'struct imx_pcm_runtime_data.playing' and
'.capturing', to avoid cancellation of hrtimer on hrtimer callback.

These ways are not necessarily efficient but actually have no trouble.
I leave them as is.

Regards

Takashi Sakamoto