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

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Message-ID: <fb95d8f8-b6a5-6848-8b28-52e2c77a90bd@linux.intel.com>
Date:   Sun, 3 Dec 2017 21:11:39 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vinod Koul <vinod.koul@...el.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 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.