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Subject[PATCH v5 0/3] fix runtime PM for SD card readers

(According to Alan Stern, "as far as I know, all") SD card readers send
MEDIA_CHANGED unit attention notification on (runtime) resume. We cannot
use runtime PM with these devices as I/O always fails in that case.

This fixes runtime PM for SD cardreaders. I'd appreciate any feedback.

To enable runtime PM for an SD cardreader number 0:0:0:0, do:

echo 0 > /sys/module/block/parameters/events_dfl_poll_msecs
echo 1000 > /sys/bus/scsi/devices/0:0:0:0/power/autosuspend_delay_ms
echo auto > /sys/bus/scsi/devices/0:0:0:0/power/control

thank you,

revision history
v5: (thank you Bart)
* simplify the sense request itself and remove unnecessary code

v4: (thank you Bart and Alan)
* send SENSE REQUEST in sd instead of adding a global scsi error flag.

v3: (thank you Bart)
* create a new BLIST entry to mark affected devices instead of the
sysfs module parameter for sd only. still, only sd implements handling
the flag for now.
* cc linux-pm list

* move module parameter to sd
* add Documentation

For the full background, the discussion started in June 2020 here:

Martin Kepplinger (3):
scsi: devinfo: add new flag BLIST_MEDIA_CHANGE
scsi: sd: send REQUEST SENSE for BLIST_MEDIA_CHANGE devices in
scsi: devinfo: add BLIST_MEDIA_CHANGE for Ultra HS-SD/MMC usb

drivers/scsi/scsi_devinfo.c | 1 +
drivers/scsi/sd.c | 26 +++++++++++++++++++++++++-
include/scsi/scsi_devinfo.h | 6 +++---
3 files changed, 29 insertions(+), 4 deletions(-)


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