[PATCH] usb: uas: expose US_FL_NO_ATA_1X in sysfs as deny_ata_passthrough

["Mateusz Jończyk" <mat.jonczyk@o2.pl>]

The uas driver blocks access to ATA passthrough commands for some
devices it considers buggy (via the US_FL_NO_ATA_1X flag in
unusual_uas.h and uas_detect.h). However, it does not expose any
meaningful information whether the command was blocked by the driver or
is genuinly not supported by the hardware. This creates a problem for
the smartmontools program and makes it difficult for it to provide a
useful error message (with instructions to disable UAS on the drive to
get SMART readings).

So, expose the information in sysfs as deny_ata_passthrough. Other
quirks may be added in the future if there is any demand.

Link: https://www.smartmontools.org/wiki/SAT-with-UAS-Linux
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
---
 drivers/usb/storage/uas.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 8655edbd66b1..aaea74297026 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -910,6 +910,25 @@ static int uas_sdev_configure(struct scsi_device *sdev,
 	return 0;
 }
 
+/* Sysfs interface */
+static ssize_t deny_ata_passthrough_show(struct device *dev, struct device_attribute *attr,
+					 char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+	struct uas_dev_info *devinfo = sdev->hostdata;
+
+	return sprintf(buf, "%d\n", !!(devinfo->flags & US_FL_NO_ATA_1X));
+}
+
+static DEVICE_ATTR_RO(deny_ata_passthrough);
+
+static struct attribute *uas_sdev_attrs[] = {
+	&dev_attr_deny_ata_passthrough.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(uas_sdev);
+
 static const struct scsi_host_template uas_host_template = {
 	.module = THIS_MODULE,
 	.name = "uas",
@@ -929,6 +948,7 @@ static const struct scsi_host_template uas_host_template = {
 	.dma_alignment = 511,
 	.dma_boundary = PAGE_SIZE - 1,
 	.cmd_size = sizeof(struct uas_cmd_info),
+	.sdev_groups = uas_sdev_groups,
 };
 
 #define UNUSUAL_DEV(id_vendor, id_product, bcdDeviceMin, bcdDeviceMax, \
-- 
2.47.3