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

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Date:   Fri, 15 May 2020 09:04:46 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Brent Lu <brent.lu@...el.com>
Cc:     alsa-devel@...a-project.org, Jaroslav Kysela <perex@...ex.cz>,
        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
Subject: Re: [PATCH] ALSA: pcm: fix incorrect hw_base increase

On Fri, May 15, 2020 at 12:09:39PM +0800, Brent Lu wrote:
> The hw_base will be increased by runtime->buffer_size frames
> unconditionally if the runtime->status->hw_ptr is not updated for over
> half of buffer time. As the hw_base increases, so does the
> runtime->status->hw_ptr which could lead to invalid return value when
> user space program calls snd_pcm_avail() function.
> 
> By updating runtime->hw_ptr_jiffies each time the HWSYNC is called,
> the hw_base will keep the same when buffer stall happens, so does the
> hw_ptr.
> 
> Signed-off-by: Brent Lu <brent.lu@...el.com>
> ---
>  sound/core/pcm_lib.c | 1 +
>  1 file changed, 1 insertion(+)

Is this a bugfix needed for older kernels as well?  When did this issue
show up?

thanks,

greg k-h