Date:   Tue, 4 Aug 2020 11:39:59 +0200
From:   Martin Kepplinger <martin.kepplinger@...i.sm>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     James Bottomley <James.Bottomley@...senpartnership.com>,
        Bart Van Assche <bvanassche@....org>,
        Can Guo <cang@...eaurora.org>, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...i.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release

On 30.07.20 17:10, Alan Stern wrote:
> On Thu, Jul 30, 2020 at 10:52:14AM +0200, Martin Kepplinger wrote:
>> 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 */
> 
> That's pretty much what James was suggesting, except for one thing: You 
> must not set sdkp->device->expecting_media_change to 1 for all devices 
> in sd_runtime_resume().  Only for devices which may generate a spurious 
> Unit Attention following runtime resume -- and maybe not even for all of 
> them, depending on what the user wants.
> 
> Alan Stern
> 

when I mount the SD card myself or via Nautilus, things work. When I put
sth like:

/dev/sda1 /mnt/sda1 auto auto,nofail 0 2

into fstab, I *still* get (constantly) when accessing the files:

[   50.838061] sd 0:0:0:0: [sda] tag#0 device offline or changed

why could that be? is there another place we would add such a new flag
(not only resume())?

                              martin

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