Re: [PATCH 1/7] soundwire: bus: use sdw_update_no_pm when initializing a device

From: Vinod Koul <vkoul@kernel.org>
To: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc: Bard Liao <yung-chuan.liao@linux.intel.com>,
	alsa-devel@alsa-project.org, tiwai@suse.de,
	gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
	ranjani.sridharan@linux.intel.com, hui.wang@canonical.com,
	broonie@kernel.org, srinivas.kandagatla@linaro.org,
	jank@cadence.com, sanyog.r.kale@intel.com,
	rander.wang@linux.intel.com, bard.liao@intel.com
Subject: Re: [PATCH 1/7] soundwire: bus: use sdw_update_no_pm when initializing a device
Date: Tue, 8 Dec 2020 10:26:00 +0530	[thread overview]
Message-ID: <20201208045600.GE8403@vkoul-mobl> (raw)
In-Reply-To: <668b4d5c-d9eb-0256-ce26-df38e32cc520@linux.intel.com>

On 07-12-20, 09:31, Pierre-Louis Bossart wrote:
> On 12/6/20 10:43 PM, Vinod Koul wrote:
> > On 05-12-20, 08:59, Pierre-Louis Bossart wrote:
> > > Thanks for the review Vinod.
> > > 
> > > On 12/5/20 1:45 AM, Vinod Koul wrote:
> > > > On 03-12-20, 04:46, Bard Liao wrote:
> > > > > From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> > > > > 
> > > > > When a Slave device is resumed, it may resume the bus and restart the
> > > > > enumeration. During that process, we absolutely don't want to call
> > > > > regular read/write routines which will wait for the resume to
> > > > > complete, otherwise a deadlock occurs.
> > > > > 
> > > > > Fixes: 60ee9be25571 ('soundwire: bus: add PM/no-PM versions of read/write functions')
> > > > 
> > > > Change looks okay, but not sure why this is a fix for adding no pm
> > > > version?
> > > 
> > > when we added the no_pm version, we missed the two cases below where
> > > sdw_update() was used and that creates a deadlock. To me that's a conceptual
> > > bug, we didn't fully use the no_pm versions, hence the Fixes tag.
> > 
> > Documentation says:
> > "A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
> > is used to make it easy to determine where a bug originated, which can help
> > review a bug fix. This tag also assists the stable kernel team in determining
> > which stable kernel versions should receive your fix. This is the preferred
> > method for indicating a bug fixed by the patch. See :ref:`describe_changes`
> > for more details."
> > 
> > I do not this this helps here as this does not help distros etc
> > I would say this is incremental development which improved a case not
> > done properly earlier, unless you would like this to be backported.. In
> > that case it helps folks...
> 
> IMHO the changes in the series are absolutely required to have a reliable
> suspend-resume operation and will need to be back-ported. When I said
> 'conceptual bug', I didn't mean a hypothetical case, I really meant that a
> proven race condition and timeouts will occur. That's not good... We will
> provide the list of this patches to distros that are known to support
> SoundWire as a 'must apply'.
> 
> If you look at the series, we provided Fixes tags for all patches except
> 'cosmetic' ones which don't fundamentally change the behavior (Patch 3,
> patch 7) or when the code has not reached Linus' tree (patch 5).
> 
> That said, 5.10 was the first release where SoundWire started to be
> functional so there's no need to apply these patches to earlier versions of
> the stable tree.
> 
> Does this help?

Yes, that helps, thanks

-- 
~Vinod