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SubjectRe: [PATCH RFC v2 1/1] scsi: pm: Leave runtime PM status alone during system resume/thaw/restore
Hi Alan,

On 2020-11-21 00:35, Alan Stern wrote:
> On Fri, Nov 20, 2020 at 12:37:22AM -0800, Can Guo wrote:
>> Runtime resume is handled by runtime PM framework, no need to forcibly
>> set runtime PM status to RPM_ACTIVE during system resume/thaw/restore.
>
> Sorry, I don't understand this explanation at all.
>
> Sure, runtime resume is handled by the runtime PM framework. But this
> patch changes the code for system resume, which is completely
> different.
>
> Following a system resume, the hardware will be at full power. We
> don't
> want the kernel to think that the device is still in runtime suspend;
> otherwise is would never put the device back into low-power mode.

How about adding below lines to the patch?

diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index 908f27f..7ebe582 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -75,9 +75,11 @@ static int scsi_dev_type_resume(struct device *dev,
const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm :
NULL;
int err = 0;

- err = cb(dev, pm);
- scsi_device_resume(to_scsi_device(dev));
- dev_dbg(dev, "scsi resume: %d\n", err);
+ if (pm_runtime_active(dev)) {
+ err = cb(dev, pm);
+ scsi_device_resume(to_scsi_device(dev));
+ dev_dbg(dev, "scsi resume: %d\n", err);
+ }

return err;
}
Whenever a device is accessed, the issuer or somewhere in the path
should do something like pm_runtime_get_sync (e.g. in sg_open()) or
pm_runtime_resume() (e.g. in blk_queue_enter()), in either sync or
async way. After the job (read/write/ioctl or whatever) is done,
either a pm_runtime_put_sync() or auto runtime suspend puts the device
back into runtime suspended/low-power mode. Since the func
scsi_bus_suspend_common() does nothing if device is already in runtime
suspended mode, scsi_dev_type_resume() should only resume the device
if it is runtime active.

Thanks,

Can Guo.

> Alan Stern
>
>> Cc: Stanley Chu <stanley.chu@mediatek.com>
>> Cc: Bart Van Assche <bvanassche@acm.org>
>> Cc: Alan Stern <stern@rowland.harvard.edu>
>> Signed-off-by: Can Guo <cang@codeaurora.org>
>> ---
>>
>> Changes since v1:
>> - Incorporated Bart's comments
>>
>> ---
>> drivers/scsi/scsi_pm.c | 24 +-----------------------
>> 1 file changed, 1 insertion(+), 23 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
>> index 3717eea..908f27f 100644
>> --- a/drivers/scsi/scsi_pm.c
>> +++ b/drivers/scsi/scsi_pm.c
>> @@ -79,25 +79,6 @@ static int scsi_dev_type_resume(struct device *dev,
>> scsi_device_resume(to_scsi_device(dev));
>> dev_dbg(dev, "scsi resume: %d\n", err);
>>
>> - if (err == 0) {
>> - pm_runtime_disable(dev);
>> - err = pm_runtime_set_active(dev);
>> - pm_runtime_enable(dev);
>> -
>> - /*
>> - * Forcibly set runtime PM status of request queue to "active"
>> - * to make sure we can again get requests from the queue
>> - * (see also blk_pm_peek_request()).
>> - *
>> - * The resume hook will correct runtime PM status of the disk.
>> - */
>> - if (!err && scsi_is_sdev_device(dev)) {
>> - struct scsi_device *sdev = to_scsi_device(dev);
>> -
>> - blk_set_runtime_active(sdev->request_queue);
>> - }
>> - }
>> -
>> return err;
>> }
>>
>> @@ -165,11 +146,8 @@ static int scsi_bus_resume_common(struct device
>> *dev,
>> */
>> if (strncmp(scsi_scan_type, "async", 5) != 0)
>> async_synchronize_full_domain(&scsi_sd_pm_domain);
>> - } else {
>> - pm_runtime_disable(dev);
>> - pm_runtime_set_active(dev);
>> - pm_runtime_enable(dev);
>> }
>> +
>> return 0;
>> }
>>
>> --
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
>> Linux Foundation Collaborative Project.
>>

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