Re: [PATCH] scsi: sd: add runtime pm to open / release

[Martin Kepplinger <martin.kepplinger@puri.sm>]

On 29.07.20 20:29, James Bottomley wrote:
> On Wed, 2020-07-29 at 14:25 -0400, Alan Stern wrote:
>> On Wed, Jul 29, 2020 at 06:43:48PM +0200, Martin Kepplinger wrote:
> [...]
>>>>> --- a/drivers/scsi/scsi_error.c
>>>>> +++ b/drivers/scsi/scsi_error.c
>>>>> @@ -554,16 +554,8 @@ int scsi_check_sense(struct scsi_cmnd
>>>>> *scmd)
>>>>>                  * so that we can deal with it there.
>>>>>                  */
>>>>>                 if (scmd->device->expecting_cc_ua) {
>>>>> -                       /*
>>>>> -                        * Because some device does not queue
>>>>> unit
>>>>> -                        * attentions correctly, we carefully
>>>>> check
>>>>> -                        * additional sense code and qualifier
>>>>> so as
>>>>> -                        * not to squash media change unit
>>>>> attention.
>>>>> -                        */
>>>>> -                       if (sshdr.asc != 0x28 || sshdr.ascq !=
>>>>> 0x00)
>>>>> {
>>>>> -                               scmd->device->expecting_cc_ua =
>>>>> 0;
>>>>> -                               return NEEDS_RETRY;
>>>>> -                       }
>>>>> +                       scmd->device->expecting_cc_ua = 0;
>>>>> +                       return NEEDS_RETRY;
>>>>
>>>> Well, yes, but you can't do this because it would lose us media
>>>> change events in the non-suspend/resume case which we really
>>>> don't want.  That's why I was suggesting a new flag.
>>>>
>>>> James
>>>
>>> also if I set expecting_cc_ua in resume() only, like I did?
>>
>> That wouldn't make any difference.  The information sent by your
>> card reader has sshdr.asc == 0x28 and sshdr.ascq == 0x00 (you can see
>> it in the log).  So because of the code here in scsi_check_sense(),
>> which you can't change, the Unit Attention sent by the card reader
>> would not be  retried even if you do set the flag in resume().
> 
> But if we had a new flag, like expecting_media_change, you could set
> that in resume and we could condition the above test in the code on it
> and reset it and do a retry if it gets set.  I'm not saying we have to
> do it this way, but it sounds like we have to do something in the
> kernel, so I think the flag will become necessary but there might be a
> bit of policy based dance around how it gets set in the kernel (to
> avoid losing accurate media change events).
> 
> James
> 

Maybe I should just start a new discussion with a patch, but the below
is what makes sense to me (when I understand you correctly) and seems to
work. I basically add a new flag, so that the old flags behave unchanged
and only call it during *runtime* resume for SD cards:


--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -553,15 +553,21 @@ int scsi_check_sense(struct scsi_cmnd *scmd)
                 * information that we should pass up to the upper-level
driver
                 * so that we can deal with it there.
                 */
-               if (scmd->device->expecting_cc_ua) {
+               if (scmd->device->expecting_cc_ua ||
+                   scmd->device->expecting_media_change) {
                        /*
                         * Because some device does not queue unit
                         * attentions correctly, we carefully check
                         * additional sense code and qualifier so as
-                        * not to squash media change unit attention.
+                        * not to squash media change unit attention;
+                        * unless expecting_media_change is set, indicating
+                        * that the media (most likely) didn't change
+                        * but a device only believes so (for example
+                        * because of suspend/resume).
                         */
-                       if (sshdr.asc != 0x28 || sshdr.ascq != 0x00) {
-                               scmd->device->expecting_cc_ua = 0;
+                       if ((sshdr.asc != 0x28 || sshdr.ascq != 0x00) ||
+                           scmd->device->expecting_media_change) {
+                               scmd->device->expecting_media_change = 0;
                                return NEEDS_RETRY;
                        }
                }
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index d90fefffe31b..b647fab2b663 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -114,6 +114,7 @@ static void sd_shutdown(struct device *);
 static int sd_suspend_system(struct device *);
 static int sd_suspend_runtime(struct device *);
 static int sd_resume(struct device *);
+static int sd_resume_runtime(struct device *);
 static void sd_rescan(struct device *);
 static blk_status_t sd_init_command(struct scsi_cmnd *SCpnt);
 static void sd_uninit_command(struct scsi_cmnd *SCpnt);
@@ -574,7 +575,7 @@ static const struct dev_pm_ops sd_pm_ops = {
        .poweroff               = sd_suspend_system,
        .restore                = sd_resume,
        .runtime_suspend        = sd_suspend_runtime,
-       .runtime_resume         = sd_resume,
+       .runtime_resume         = sd_resume_runtime,
 };

 static struct scsi_driver sd_template = {
@@ -3652,6 +3653,21 @@ static int sd_resume(struct device *dev)
        return ret;
 }

+static int sd_resume_runtime(struct device *dev)
+{
+       struct scsi_disk *sdkp = dev_get_drvdata(dev);
+
+       /* Some SD cardreaders report media change when resuming from
suspend
+        * because they can't keep track during suspend. */
+
+       /* XXX This is not unproblematic though: We won't notice when a card
+        * was really changed during runtime suspend! We basically rely
on users
+        * to unmount or suspend before doing so. */
+       sdkp->device->expecting_media_change = 1;
+
+       return sd_resume(dev);
+}
+
 /**
  *     init_sd - entry point for this driver (both when built in or when
  *     a module).
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index bc5909033d13..8c8f053f71c8 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -169,6 +169,8 @@ struct scsi_device {
                                 * this device */
        unsigned expecting_cc_ua:1; /* Expecting a CHECK_CONDITION/UNIT_ATTN
                                     * because we did a bus reset. */
+       unsigned expecting_media_change:1; /* Expecting media change
ASC/ASCQ
+                                             when it actually doesn't
change */
        unsigned use_10_for_rw:1; /* first try 10-byte read / write */
        unsigned use_10_for_ms:1; /* first try 10-byte mode sense/select */
        unsigned set_dbd_for_ms:1; /* Set "DBD" field in mode sense */