linux-kernel - Re: [PATCH v2 0/4] ALSA: compress_offload: Add 64-bit safe timestamp API

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Message-ID: <aHD7/9MZbcOmn+08@opensource.cirrus.com>
Date: Fri, 11 Jul 2025 12:56:47 +0100
From: Charles Keepax <ckeepax@...nsource.cirrus.com>
To: Joris Verhaegen <verhaegen@...gle.com>
Cc: Vinod Koul <vkoul@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>,
        David Rhodes <david.rhodes@...rus.com>,
        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
Subject: Re: [PATCH v2 0/4] ALSA: compress_offload: Add 64-bit safe timestamp
 API

On Fri, Jul 11, 2025 at 10:36:26AM +0100, Joris Verhaegen wrote:
> The current compress offload timestamping API relies on
> struct snd_compr_tstamp, whose cumulative counters like
> copied_total are defined as __u32. On long-running high-resolution
> audio streams, these 32-bit counters can overflow,
> causing incorrect availability calculations.
> 
> This patch series introduces a parallel, 64-bit safe API to solve
> this problem while maintaining perfect backward compatibility with the
> existing UAPI. A new pointer64 operation and corresponding ioctls
> are added to allow the kernel to track counters using u64 and expose
> these full-width values to user-space.
> 
> The series is structured as follows:
> 
> Patch 1: Introduces the new internal pointer64 op, refactors the
> core logic to use it, and defines the new UAPI structs.
> 
> Patch 2: Exposes the SNDRV_COMPRESS_TSTAMP64 ioctl.
> 
> Patch 3: Exposes the corresponding SNDRV_COMPRESS_AVAIL64 ioctl.
> 
> Patch 4: Implements the new .pointer64 operation in various ASoC
> drivers that support compress offload.
> 
> This series has been tested on a Pixel 9 device. All compress offload
> use cases, including long-running playback, were verified to work
> correctly with the new 64-bit API, and no regressions were observed
> when using the legacy API.
> 
> Thanks,
> Joris (George) Verhaegen
> 
> Signed-off-by: Joris Verhaegen <verhaegen@...gle.com>
> 
> ---

Would it not be slightly simpler to just update all the in kernel
bits to use 64-bit and then only convert to 32-bit for the
existing 32-bit IOCTLs? Why do we need 32-bit callbacks into the
drivers for example?

Thanks,
Charles