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

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Date:   Fri, 15 May 2020 12:09:39 +0800
From:   Brent Lu <brent.lu@...el.com>
To:     alsa-devel@...a-project.org
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Richard Fontana <rfontana@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brent Lu <brent.lu@...el.com>,
        paulhsia <paulhsia@...omium.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] ALSA: pcm: fix incorrect hw_base increase

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(+)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 872a852..d531e1b 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -433,6 +433,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
 
  no_delta_check:
 	if (runtime->status->hw_ptr == new_hw_ptr) {
+		runtime->hw_ptr_jiffies = curr_jiffies;
 		update_audio_tstamp(substream, &curr_tstamp, &audio_tstamp);
 		return 0;
 	}
-- 
2.7.4