linux-kernel - Re: [PATCH RFC v1 1/1] scsi: pm: Leave runtime resume along if block layer PM is enabled

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Date:   Sat, 14 Nov 2020 12:57:21 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Can Guo <cang@...eaurora.org>, asutoshd@...eaurora.org,
        nguyenb@...eaurora.org, hongwus@...eaurora.org,
        ziqichen@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com
Cc:     Stanley Chu <stanley.chu@...iatek.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH RFC v1 1/1] scsi: pm: Leave runtime resume along if block
 layer PM is enabled

On 11/12/20 10:30 PM, Can Guo wrote:
> If block layer runtime PM is enabled for one SCSI device, then there is
> no need to forcibly change the SCSI device and its request queue's runtime
> PM status to active in scsi_dev_type_resume(), since block layer PM shall
> resume the SCSI device on the demand of bios.

Please change "along" into "alone" in the subject of this patch (if that
is what you meant).

> +	if (scsi_is_sdev_device(dev)) {
> +		struct scsi_device *sdev;
>  
> +		sdev = to_scsi_device(dev);

A minor comment: I think that "struct scsi_device *sdev =
to_scsi_device(dev);" fits on a single line.

> +		 * If block layer runtime PM is enabled for the SCSI device,
> +		 * let block layer PM handle its runtime PM routines.

Please change "its runtime PM routines" into "runtime resume" or
similar. I think that will make the comment more clear.

> +		if (sdev->request_queue->dev)
> +			return err;
> +	}

The 'dev' member only exists in struct request_queue if CONFIG_PM=y so
the above won't compile if CONFIG_PM=n. How about adding a function in
include/linux/blk-pm.h to check whether or not runtime PM has been enabled?

Otherwise this patch looks good to me.

Thanks,

Bart.