linux-kernel - Re: [PATCH] ALSA: pcm: fix incorrect hw

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Date:   Fri, 15 May 2020 11:30:54 +0200
From:   Jaroslav Kysela <perex@...ex.cz>
To:     "Lu, Brent" <brent.lu@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        Takashi Iwai <tiwai@...e.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Richard Fontana <rfontana@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        paulhsia <paulhsia@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: pcm: fix incorrect hw_base increase

Dne 15. 05. 20 v 11:04 Lu, Brent napsal(a):
>>
>> Is this a bugfix needed for older kernels as well?  When did this issue show
>> up?
>>
>> thanks,
>>
>> greg k-h
> 
> It happens when DMA stop moving data from host to DSP/DAI for a long time
> (> half of buffer time). I know host driver should do something about it. But if
> not, the HWSYNC will keep increasing the hw_base and hw_ptr and confuses
> user space program.

I'm afraid, but with this code, you turn off the hw_ptr jiffies code. It would 
be better to fix the driver in this case (return the updated / estimated DMA 
pointer, increase DMA buffer size etc.). This "lag" is unacceptable.

						Jaroslav

> 
> Regards,
> Brent
> 


-- 
Jaroslav Kysela <perex@...ex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.