[alsa-devel] [PATCH 0/7] ALSA: Fix/improve PCM ack callback

[Takashi Sakamoto]

Hi,

On May 22 2017 04:02, Takashi Iwai wrote:
> Hi,
> 
> this is a series of patches to fix the potential bugs in PCM ack
> callback using the pcm-indirect helper functions, and also to enhance
> the ack callback to be called properly in all appl_ptr updates, as
> similarly done by Pierre and Subhransu's patches.
> 
> The changes in the pcm-indirect helper code and its users are fairly
> trivial, just passing the error code back.
> 
> ARM/R-Pi people are Cc'ed because of bcm2835-audio driver.
> 
> 
> Takashi
> 
> ===
> 
> Takashi Iwai (7):
>    ALSA: pcm: Fix negative appl_ptr handling in pcm-indirect helpers
>    ALSA: mips: Deliver indirect-PCM transfer error
>    ALSA: cs46xx: Deliver indirect-PCM transfer error
>    ALSA: emu10k1: Deliver indirect-PCM transfer error
>    ALSA: rme32: Deliver indirect-PCM transfer error
>    staging: bcm2835-audio: Deliver indirect-PCM transfer error
>    ALSA: pcm: Call ack() whenever appl_ptr is updated
> 
>   .../vc04_services/bcm2835-audio/bcm2835-pcm.c      |  5 +--
>   include/sound/pcm-indirect.h                       | 10 ++++-
>   sound/core/pcm_native.c                            | 46 +++++++++++++++++-----
>   sound/mips/hal2.c                                  | 14 +++----
>   sound/pci/cs46xx/cs46xx_lib.c                      |  8 ++--
>   sound/pci/emu10k1/emupcm.c                         |  4 +-
>   sound/pci/rme32.c                                  | 10 ++---
>   7 files changed, 63 insertions(+), 34 deletions(-)

I mostly agree with this patchset, except for one point.

The added helper function, apply_appl_ptr(), copies given data to the 
runtime for application-side pointer, then call 'struct 
snd_pcm_ops.ack'. We have similar code block in 'sound/core/pcm_lib.c', 
as well. See 'snd_pcm_lib_write1()' and 'snd_pcm_lib_read1()'.

In a point of code maintenance, it's better to share the function 
between two objects; pcm_native.o and pcm_lib.o.

For instance, I can propose a below patch. I expect you to squash it up 
within one of your patches.

========== 8< ----------

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index ab4b1d1e44ee..9d048f91bd3f 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -2010,6 +2010,12 @@ typedef int (*transfer_f)(struct 
snd_pcm_substream *substream, unsigned int hwof
  			  unsigned long data, unsigned int off,
  			  snd_pcm_uframes_t size);

+/* This symbol is shared by several relocatable objects for the same shared
+ * object.
+ */
+int snd_pcm_apply_appl_ptr(struct snd_pcm_substream *substream,
+			  snd_pcm_uframes_t appl_ptr);
+
  static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream 
*substream,
  					    unsigned long data,
  					    snd_pcm_uframes_t size,
@@ -2087,11 +2093,9 @@ static snd_pcm_sframes_t 
snd_pcm_lib_write1(struct snd_pcm_substream *substream,
  			break;
  		}
  		appl_ptr += frames;
-		if (appl_ptr >= runtime->boundary)
-			appl_ptr -= runtime->boundary;
-		runtime->control->appl_ptr = appl_ptr;
-		if (substream->ops->ack)
-			substream->ops->ack(substream);
+		err = snd_pcm_apply_appl_ptr(substream, appl_ptr);
+		if (err < 0)
+			goto _end_unlock;

  		offset += frames;
  		size -= frames;
@@ -2321,9 +2325,9 @@ static snd_pcm_sframes_t snd_pcm_lib_read1(struct 
snd_pcm_substream *substream,
  		appl_ptr += frames;
  		if (appl_ptr >= runtime->boundary)
  			appl_ptr -= runtime->boundary;
-		runtime->control->appl_ptr = appl_ptr;
-		if (substream->ops->ack)
-			substream->ops->ack(substream);
+		err = snd_pcm_apply_appl_ptr(substream, appl_ptr);
+		if (err < 0)
+			goto _end_unlock;

  		offset += frames;
  		size -= frames;
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 7bc4a0bbad6f..0b176b35ade1 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2456,9 +2456,11 @@ static int do_pcm_hwsync(struct snd_pcm_substream 
*substream)
  }

  /* update to the given appl_ptr and call ack callback if needed;
- * when an error is returned, take back to the original value
+ * when an error is returned, take back to the original value.
+ * The given argument should have valid value as application pointer on PCM
+ * buffer.
   */
-static int apply_appl_ptr(struct snd_pcm_substream *substream,
+int snd_pcm_apply_appl_ptr(struct snd_pcm_substream *substream,
  			  snd_pcm_uframes_t appl_ptr)
  {
  	struct snd_pcm_runtime *runtime = substream->runtime;
@@ -2492,7 +2494,7 @@ static snd_pcm_sframes_t forward_appl_ptr(struct 
snd_pcm_substream *substream,
  	appl_ptr = runtime->control->appl_ptr + frames;
  	if (appl_ptr >= (snd_pcm_sframes_t)runtime->boundary)
  		appl_ptr -= runtime->boundary;
-	ret = apply_appl_ptr(substream, appl_ptr);
+	ret = snd_pcm_apply_appl_ptr(substream, appl_ptr);
  	return ret < 0 ? ret : frames;
  }

@@ -2512,7 +2514,7 @@ static snd_pcm_sframes_t rewind_appl_ptr(struct 
snd_pcm_substream *substream,
  	appl_ptr = runtime->control->appl_ptr - frames;
  	if (appl_ptr < 0)
  		appl_ptr += runtime->boundary;
-	ret = apply_appl_ptr(substream, appl_ptr);
+	ret = snd_pcm_apply_appl_ptr(substream, appl_ptr);
  	return ret < 0 ? ret : frames;
  }

@@ -2644,7 +2646,8 @@ static int snd_pcm_sync_ptr(struct 
snd_pcm_substream *substream,
  	}
  	snd_pcm_stream_lock_irq(substream);
  	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_APPL)) {
-		err = apply_appl_ptr(substream, sync_ptr.c.control.appl_ptr);
+		err = snd_pcm_apply_appl_ptr(substream,
+					     sync_ptr.c.control.appl_ptr);
  		if (err < 0) {
  			snd_pcm_stream_unlock_irq(substream);
  			return err;


Regards

Takashi Sakamoto