Re: [PATCH V0 1/1] ALSA: pcm: fix blocking while loop in snd_pcm_update_hw_ptr0()

On Fri, 25 Feb 2022 13:26:36 +0100, Raghu Ballappa Bankapur wrote:

Hi Takashi,

Thanks for your feedback.

I see your below statement

But, having either this zero check or minimal hw_ptr_buffer_jiffies=1 would be good in anyway, even if we add more check for the hw_params for no-period-wakeup case.

Please review if those changes are Ok

If you mean about your posted patch for "those changes", as Jaroslav suggested in the thread, we may take a different approach: just set the minimal hw_ptr_buffer_jiffies to 1.

Could you try this and submit the fix if that works for you?

thanks,

Takashi

Regards Raghu

On 2/25/2022 4:53 PM, Takashi Iwai wrote:

On Fri, 25 Feb 2022 11:52:05 +0100,
Jaroslav Kysela wrote:

    On 25. 02. 22 11:39, Raghu Bankapur wrote:

        When period interrupts are disabled, while loop in snd_pcm_update_hw_ptr0()
        results in the machine locking up if runtime->hw_ptr_buffer_jiffies is 0.
        Validate runtime->hw_ptr_buffer_jiffies value before while loop to avoid
        delta check.

    I would set hw_ptr_buffer_jiffies to 1 in this case in snd_pcm_post_start().

I thought of it at the first glance, but after reading the code again,
I doubt whether it makes sense at all to allow this condition.
Since the buffer size is too small and the rate is too high, we can't
calculate the buffer crossing condition accurately under such
condition.

But, having either this zero check or minimal hw_ptr_buffer_jiffies=1
would be good in anyway, even if we add more check for the hw_params
for no-period-wakeup case.

thanks,

Takashi