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

Martin Kepplinger
2020-07-30T08:52:57Z

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 */