From: Vinod Koul <vkoul@kernel.org>
To: Bard Liao <yung-chuan.liao@linux.intel.com>
Cc: alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org,
gregkh@linuxfoundation.org, srinivas.kandagatla@linaro.org,
rander.wang@linux.intel.com,
pierre-louis.bossart@linux.intel.com, sanyog.r.kale@intel.com,
bard.liao@intel.com
Subject: Re: [PATCH] soundwire: cadence: add paranoid check on self-clearing bits
Date: Mon, 2 Aug 2021 09:20:20 +0530 [thread overview]
Message-ID: <YQdrfNA08UITBjvB@matsya> (raw)
In-Reply-To: <20210714051349.13064-1-yung-chuan.liao@linux.intel.com>
On 14-07-21, 13:13, Bard Liao wrote:
> From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
>
> The Cadence IP exposes a small number of self-clearing bits in
> the MCP_CONTROL and MCP_CONFIG_UPDATE registers.
>
> We currently do not check that those bits are indeed cleared,
> e.g. during resume operations. That could lead to resuming peripheral
> devices too early.
>
> In addition, if we happen to read these registers, update one of the
> fields and write the register back, we may be writing stale data that
> might have been cleared in hardware. These sort of race conditions
> could lead to e.g. doing a hw_reset twice or stopping a clock that
> just restarted. There is no clear way of avoiding these potential race
> conditions other than making sure that these registers fields are
> cleared before any read-modify-write sequence. If we detect this sort
> of errors, we only log them since there is no clear recovery
> possible. The only way out is likely to restart the IP with a
> suspend/resume cycle.
>
> Note that the checks are performed before updating the registers, as
> well as after the Intel 'sync go' sequence in multi-link mode. That
> should cover both the start and end of suspend/resume hardware
> configurations. The Multi-Master mode gates the configuration updates
> until the 'sync go' signal is asserted, so we only check on init and
> after the end of the 'sync go' sequence.
>
> The duration of the usleep_range() was defined by the GSYNC frequency
> used in multi-master mode. With a 4kHz frequency, any configuration
> change might be deferred by up to 250us. Extending the range to
> 1000-1500us should guarantee that the configuration change is
> completed without any significant impact on the overall resume
> time.
There were some checkpatch warns, but I think code will looks worse if
we split lines up, so applied now
--
~Vinod
prev parent reply other threads:[~2021-08-02 3:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-14 5:13 [PATCH] soundwire: cadence: add paranoid check on self-clearing bits Bard Liao
2021-08-02 3:50 ` Vinod Koul [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YQdrfNA08UITBjvB@matsya \
--to=vkoul@kernel.org \
--cc=alsa-devel@alsa-project.org \
--cc=bard.liao@intel.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pierre-louis.bossart@linux.intel.com \
--cc=rander.wang@linux.intel.com \
--cc=sanyog.r.kale@intel.com \
--cc=srinivas.kandagatla@linaro.org \
--cc=yung-chuan.liao@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).