On 10/7/21 9:24 AM, Alan Stern wrote:

On Wed, Oct 06, 2021 at 02:54:53PM -0700, Bart Van Assche wrote:

quoted

The following query shows which drivers define callbacks that are called
by the power management support code in the SCSI core (scsi_pm.c):

$ git grep -nHEwA16 "$(echo $(git grep -h 'scsi_register_driver(&' |
       sed 's/.*&//;s/\..*//') | sed 's/ /|/g')" |
     grep '\.pm[[:blank:]]*=[[:blank:]]'
drivers/scsi/sd.c-620-		.pm		= &sd_pm_ops,
drivers/scsi/sr.c-100-		.pm		= &sr_pm_ops,
drivers/scsi/ufs/ufshcd.c-9765-		.pm = &ufshcd_wl_pm_ops,

Since unconditionally runtime resuming a device during system resume is
not necessary, remove that code. Modify the SCSI disk (sd) driver such
that it follows the same approach as the UFS driver, namely to skip
system suspend and resume for devices that are runtime suspended. The
CD-ROM code does not need to be updated since its PM callbacks do not
affect the device power state.

You may already be aware of this, but in case you aren't...

The PM core already contains some provisions for handling these kinds
of things.  They are described in
Documentation/driver-api/pm/devices.rst.  See particularly the parts
relating to the DPM_FLAG_NO_DIRECT_COMPLETE, DPM_FLAG_SMART_PREPARE,
DPM_FLAG_SMART_SUSPEND, DPM_FLAG_MAY_SKIP_RESUME, and
power.direct_complete flags.

A follow-up patch after this series might be able to take advantage of
these facilities.

Hi Alan,

Thanks for the feedback. I was not yet aware of these flags. Since using 
these flags would make patch 3/3 only a few lines shorter and would make 
it harder to review for anyone who is not familiar with the DPM flags, 
I'm considering to keep patch 3/3 as is (this means not using the DPM 
flags).

Thanks,

Bart.