Re: USB mass-storage devices and READ CAPACITY(16)

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Fri, 15 Jun 2012, Alan Stern wrote:

> On Fri, 15 Jun 2012, Hans de Goede wrote:
> 
> > Hi,
> > 
> > On 06/15/2012 08:20 PM, Alan Stern wrote:
> > > As we can see from recent bug reports, a lot of USB mass-storage
> > > devices cannot handle READ CAPACITY(16) commands properly.  They send
> > > back garbage and are unusable as a result.
> > >
> > > Should we go ahead and set a flag on all these devices, telling the sd
> > > driver to try READ CAPACITY(10) first?  That's a lot easier than adding
> > > more and more entries to unusual_devs.h.
> > 
> > That certainly sound reasonable to me. Note that the 071b:3203 really
> > needs the US_FL_NO_READ_CAPACITY_16 flag though, as it wrongly reports
> > a capacity of -1 when there is no sd card in its slot, and in response
> > to that the kernel tries READ CAPACITY(16) and things go downhill
> > from there...
> 
> Yes, we need to be able to have both flags set for the same device.  
> For that card reader they would mean try READ CAPACITY(10) first, and 
> if it fails, don't try READ CAPACITY(16).

In other words, I'm suggesting we adopt this patch and get rid Hans's 
new unusual_devs entry.

Alan Stern




Index: usb-3.4/include/scsi/scsi_device.h
===================================================================
--- usb-3.4.orig/include/scsi/scsi_device.h
+++ usb-3.4/include/scsi/scsi_device.h
@@ -151,6 +151,7 @@ struct scsi_device {
 					   SD_LAST_BUGGY_SECTORS */
 	unsigned no_read_disc_info:1;	/* Avoid READ_DISC_INFO cmds */
 	unsigned no_read_capacity_16:1; /* Avoid READ_CAPACITY_16 cmds */
+	unsigned try_rc_10_first:1;	/* Try READ_CAPACACITY_10 first */
 	unsigned is_visible:1;	/* is the device visible in sysfs */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
Index: usb-3.4/drivers/scsi/sd.c
===================================================================
--- usb-3.4.orig/drivers/scsi/sd.c
+++ usb-3.4/drivers/scsi/sd.c
@@ -1899,6 +1899,8 @@ static int sd_try_rc16_first(struct scsi
 {
 	if (sdp->host->max_cmd_len < 16)
 		return 0;
+	if (sdp->try_rc_10_first)
+		return 0;
 	if (sdp->scsi_level > SCSI_SPC_2)
 		return 1;
 	if (scsi_device_protection(sdp))
Index: usb-3.4/drivers/usb/storage/scsiglue.c
===================================================================
--- usb-3.4.orig/drivers/usb/storage/scsiglue.c
+++ usb-3.4/drivers/usb/storage/scsiglue.c
@@ -202,6 +202,12 @@ static int slave_configure(struct scsi_d
 		if (us->fflags & US_FL_NO_READ_CAPACITY_16)
 			sdev->no_read_capacity_16 = 1;
 
+		/*
+		 * Many devices do not respond properly to READ_CAPACITY_16.
+		 * Tell the SCSI layer to try READ_CAPACITY_10 first.
+		 */
+		sdev->try_rc_10_first = 1;
+
 		/* assume SPC3 or latter devices support sense size > 18 */
 		if (sdev->scsi_level > SCSI_SPC_2)
 			us->fflags |= US_FL_SANE_SENSE;

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