linux-kernel - Re: [PATCH] soundwire: intel: don't save hw

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Message-ID: <ZDaB4Nea32pNWpeN@matsya>
Date:   Wed, 12 Apr 2023 15:33:12 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Bard Liao <yung-chuan.liao@...ux.intel.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        pierre-louis.bossart@...ux.intel.com, bard.liao@...el.com
Subject: Re: [PATCH] soundwire: intel: don't save hw_params for use in prepare

On 21-03-23, 10:26, Bard Liao wrote:
> From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> 
> The existing code copies the hw_params pointer and reuses it later in
> .prepare, specifically to re-initialize the ALH DMA channel
> information that's lost in suspend-resume cycles.
> 
> This is not needed, we can directly access the information from the
> substream/rtd - as done for the HDAudio DAIs in
> sound/soc/sof/intel/hda-dai.c
> 
> In addition, using the saved pointer causes the suspend-resume test
> cases to fail on specific platforms, depending on which version of GCC
> is used. Péter Ujfalusi and I have spent long hours to root-cause this
> problem that was reported by the Intel CI first with 6.2-rc1 and again
> v6.3-rc1. In the latter case we were lucky that the problem was 100%
> reproducible on local test devices, and found out that adding a
> dev_dbg() or adding a call to usleep_range() just before accessing the
> saved pointer "fixed" the issue. With errors appearing just by
> changing the compiler version or minor changes in the code generated,
> clearly we have a memory management Heisenbug.
> 
> The root-cause seems to be that the hw_params pointer is not
> persistent. The soc-pcm code allocates the hw_params structure on the
> stack, and passes it to the BE dailink hw_params and DAIs
> hw_params. Saving such a pointer and reusing it later during the
> .prepare stage cannot possibly work reliably, it's broken-by-design
> since v5.10. It's astonishing that the problem was not seen earlier.
> 
> This simple fix will have to be back-ported to -stable, due to changes
> to avoid the use of the get/set_dmadata routines this patch will only
> apply on kernels older than v6.1.

Applied, thanks

-- 
~Vinod