linux-kernel - Re: [alsa-devel] [PATCH v4 09/15] soundwire: Add slave status handling

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Date:   Mon, 4 Dec 2017 08:51:00 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        ALSA <alsa-devel@...a-project.org>, Mark <broonie@...nel.org>,
        Takashi <tiwai@...e.de>, patches.audio@...el.com,
        alan@...ux.intel.com,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Sagar Dharia <sdharia@...eaurora.org>,
        srinivas.kandagatla@...aro.org, plai@...eaurora.org,
        Sudheer Papothi <spapothi@...eaurora.org>
Subject: Re: [alsa-devel] [PATCH v4 09/15] soundwire: Add slave status
 handling

On Sun, Dec 03, 2017 at 09:11:39PM -0600, Pierre-Louis Bossart wrote:
> On 12/3/17 11:11 AM, Vinod Koul wrote:
> >On Fri, Dec 01, 2017 at 05:52:03PM -0600, Pierre-Louis Bossart wrote:
> >
> >>>+		status = sdw_read(slave, SDW_DP0_INT);
> >>>+		if (status < 0) {
> >>>+			dev_err(slave->bus->dev,
> >>>+				"SDW_DP0_INT read failed:%d", status);
> >>>+			return status;
> >>>+		}
> >>>+
> >>>+		count++;
> >>>+
> >>>+		/* we can get alerts while processing so keep retrying */
> >>
> >>This is not incorrect, but this goes beyond what the spec requires.
> >>
> >>The additional read is to make sure some interrupts are not lost due to a
> >>known race condition. It would be enough to mask the status read the second
> >>time to only check if the interrupts sources which were cleared are still
> >>signaling something.
> >>
> >>With the code as it is, you may catch *new* interrupt sources, which could
> >>impact the arbitration/priority/policy in handling interrupts. It's not
> >>necessarily bad, but you'd need to document whether you want to deal with
> >>the race condition described in the MIPI spec or try to be smarter.
> >
> >This was based on your last comment, lets discuss more offline on this to
> >see what else is required here.
> 
> I am fine if you leave the code as is for now, it's not bad but can be
> optimized.

Not bad is not good here :)

Okay I still havent grabbed my coffee, so help me out here. I am not sure I
understand here, can you point me to the part of spec handling you were
referring and what should be *ideally* done

-- 
~Vinod