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

Alan Stern
2020-07-30T15:10:35Z

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