linux-kernel - Re: [PATCH v4 2/3] ALSA: compress_offload: Add SNDRV_COMPRESS

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Message-ID: <CAAntYmLYVeMEpEtzhhMZ_kyAuwqv5suQK=rjF4ixgu1QH3yk=w@mail.gmail.com>
Date: Wed, 6 Aug 2025 12:34:46 +0100
From: George Verhaegen <verhaegen@...gle.com>
To: Vinod Koul <vkoul@...nel.org>
Cc: Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, Liam Girdwood <lgirdwood@...il.com>, 
	Mark Brown <broonie@...nel.org>, Cezary Rojewski <cezary.rojewski@...el.com>, 
	Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>, 
	Bard Liao <yung-chuan.liao@...ux.intel.com>, 
	Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>, 
	Kai Vehmanen <kai.vehmanen@...ux.intel.com>, 
	Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>, Srinivas Kandagatla <srini@...nel.org>, 
	Daniel Baluta <daniel.baluta@....com>, Orson Zhai <orsonzhai@...il.com>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, Chunyan Zhang <zhang.lyra@...il.com>, 
	Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>, Masami Hiramatsu <mhiramat@...nel.org>, 
	kernel-team@...roid.com, linux-sound@...r.kernel.org, 
	linux-kernel@...r.kernel.org, patches@...nsource.cirrus.com, 
	linux-arm-msm@...r.kernel.org, sound-open-firmware@...a-project.org, 
	linux-arm-kernel@...ts.infradead.org, Miller Liang <millerliang@...gle.com>
Subject: Re: [PATCH v4 2/3] ALSA: compress_offload: Add SNDRV_COMPRESS_TSTAMP64
 ioctl

On Tue, 05 Aug 2025 06:47:59 +0200,
Vinod Koul wrote:
>
> On 01-08-25, 10:27, Joris Verhaegen wrote:
> > The previous patch introduced the internal infrastructure for handling
> > 64-bit timestamps. This patch exposes this capability to user-space.
> >
> > Define the new ioctl command SNDRV_COMPRESS_TSTAMP64, which allows
> > applications to fetch the overflow-safe struct snd_compr_tstamp64.
> >
> > The ioctl dispatch table is updated to handle the new command by
> > calling a new snd_compr_tstamp64 handler, while the legacy path is
> > renamed to snd_compr_tstamp32 for clarity.
> >
> > This patch bumps the SNDRV_COMPRESS_VERSION to 0.4.0.
> >
> > Reviewed-by: Miller Liang <millerliang@...gle.com>
> > Tested-by: Joris Verhaegen <verhaegen@...gle.com>
> > Signed-off-by: Joris Verhaegen <verhaegen@...gle.com>
> > ---
> >  include/uapi/sound/compress_offload.h |  5 +++--
> >  sound/core/compress_offload.c         | 19 +++++++++++++------
> >  2 files changed, 16 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/uapi/sound/compress_offload.h b/include/uapi/sound/compress_offload.h
> > index abd0ea3f86ee..70b8921601f9 100644
> > --- a/include/uapi/sound/compress_offload.h
> > +++ b/include/uapi/sound/compress_offload.h
> > @@ -13,8 +13,7 @@
> >  #include <sound/asound.h>
> >  #include <sound/compress_params.h>
> >
> > -
> > -#define SNDRV_COMPRESS_VERSION SNDRV_PROTOCOL_VERSION(0, 3, 0)
> > +#define SNDRV_COMPRESS_VERSION SNDRV_PROTOCOL_VERSION(0, 4, 0)
> >  /**
> >   * struct snd_compressed_buffer - compressed buffer
> >   * @fragment_size: size of buffer fragment in bytes
> > @@ -208,6 +207,7 @@ struct snd_compr_task_status {
> >   * Note: only codec params can be changed runtime and stream params cant be
> >   * SNDRV_COMPRESS_GET_PARAMS: Query codec params
> >   * SNDRV_COMPRESS_TSTAMP: get the current timestamp value
> > + * SNDRV_COMPRESS_TSTAMP64: get the current timestamp value in 64 bit format
> >   * SNDRV_COMPRESS_AVAIL: get the current buffer avail value.
> >   * This also queries the tstamp properties
> >   * SNDRV_COMPRESS_PAUSE: Pause the running stream
> > @@ -230,6 +230,7 @@ struct snd_compr_task_status {
> >                                              struct snd_compr_metadata)
> >  #define SNDRV_COMPRESS_TSTAMP              _IOR('C', 0x20, struct snd_compr_tstamp)
> >  #define SNDRV_COMPRESS_AVAIL               _IOR('C', 0x21, struct snd_compr_avail)
> > +#define SNDRV_COMPRESS_TSTAMP64            _IOR('C', 0x22, struct snd_compr_tstamp64)
> >  #define SNDRV_COMPRESS_PAUSE               _IO('C', 0x30)
> >  #define SNDRV_COMPRESS_RESUME              _IO('C', 0x31)
> >  #define SNDRV_COMPRESS_START               _IO('C', 0x32)
> > diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> > index d3164aa07158..445220fdb6a0 100644
> > --- a/sound/core/compress_offload.c
> > +++ b/sound/core/compress_offload.c
> > @@ -736,18 +736,23 @@ snd_compr_set_metadata(struct snd_compr_stream *stream, unsigned long arg)
> >     return retval;
> >  }
> >
> > -static inline int
> > -snd_compr_tstamp(struct snd_compr_stream *stream, unsigned long arg)
> > +static inline int snd_compr_tstamp(struct snd_compr_stream *stream,
> > +                              unsigned long arg, bool is_32bit)
> >  {
> >     struct snd_compr_tstamp64 tstamp64 = { 0 };
> >     struct snd_compr_tstamp tstamp32 = { 0 };
> > +   const void *copy_from = &tstamp64;
> > +   size_t copy_size = sizeof(tstamp64);
> >     int ret;
> >
> >     ret = snd_compr_update_tstamp(stream, &tstamp64);
> >     if (ret == 0) {
> > -           snd_compr_tstamp32_from_64(&tstamp32, &tstamp64);
> > -           ret = copy_to_user((struct snd_compr_tstamp __user *)arg,
> > -                              &tstamp32, sizeof(tstamp32)) ?
> > +           if (is_32bit) {
> > +                   snd_compr_tstamp32_from_64(&tstamp32, &tstamp64);
> > +                   copy_from = &tstamp32;
> > +                   copy_size = sizeof(tstamp32);
> > +           }
>
> Most of the applications and people would be 32bit right now and we
> expect this to progressively change, but then this imposes a penalty as
> default path is 64 bit, since we expect this ioctl to be called very
> frequently, should we do this optimization for 64bit here?

Valid point about optimizing the common path. But since the underlying
.pointer op was changed in the patch V3 to always return a 64-bit
snd_compr_tstamp64, there is no longer a "native" 32-bit path to fetch.

Any call to the legacy SNDRV_COMPRESS_TSTAMP ioctl must fetch the 64-bit
value and then truncate it down. The current patch reflects this by sharing the
common 64-bit fetch and then conditionally performing the truncation to 32-bit.
Splitting the function would result in two functions that both call
snd_compr_update_tstamp() to get the 64-bit data, so there would be code
duplication with no performance gain.

Thanks,
George