[DONTCOMMIT/WIP] gspca: Check device presence before accessing hardware

[Ezequiel Garcia <ezequiel@collabora.com>]

sd_desc->stop0 and sd_desc->stopN hooks are meant to access
the device hardware, stopping the transfer. Thus, hardware
presence should be checked before calling them.

This means that sd_desc.start is not allowed to allocate resources,
since sd_desc.stop0 and sd_desc.stopN won't be releasing when
the USB device is disconnected.

TODO: Check what's the deal with the konica device, which is allocating
URB memory in sd_desc.start. This seems wrong.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
---
 drivers/media/usb/gspca/gspca.c | 11 ++++++-----
 drivers/media/usb/gspca/gspca.h |  6 +++---
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/media/usb/gspca/gspca.c b/drivers/media/usb/gspca/gspca.c
index 4d7517411cc2..98b68a7a52c0 100644
--- a/drivers/media/usb/gspca/gspca.c
+++ b/drivers/media/usb/gspca/gspca.c
@@ -745,15 +745,16 @@ static void gspca_stream_off(struct gspca_dev *gspca_dev)
 {
 	gspca_dev->streaming = false;
 	gspca_dev->usb_err = 0;
-	if (gspca_dev->sd_desc->stopN)
+	if (gspca_dev->present && gspca_dev->sd_desc->stopN)
 		gspca_dev->sd_desc->stopN(gspca_dev);
 	destroy_urbs(gspca_dev);
 	gspca_input_destroy_urb(gspca_dev);
-	gspca_set_alt0(gspca_dev);
-	if (gspca_dev->present)
+	if (gspca_dev->present) {
+		gspca_set_alt0(gspca_dev);
 		gspca_input_create_urb(gspca_dev);
-	if (gspca_dev->sd_desc->stop0)
-		gspca_dev->sd_desc->stop0(gspca_dev);
+		if (gspca_dev->sd_desc->stop0)
+			gspca_dev->sd_desc->stop0(gspca_dev);
+	}
 	gspca_dbg(gspca_dev, D_STREAM, "stream off OK\n");
 }
 
diff --git a/drivers/media/usb/gspca/gspca.h b/drivers/media/usb/gspca/gspca.h
index b0ced2e14006..e0ca120d2e31 100644
--- a/drivers/media/usb/gspca/gspca.h
+++ b/drivers/media/usb/gspca/gspca.h
@@ -105,13 +105,13 @@ struct sd_desc {
 	cam_cf_op config;	/* called on probe */
 	cam_op init;		/* called on probe and resume */
 	cam_op init_controls;	/* called on probe */
-	cam_op start;		/* called on stream on after URBs creation */
+	cam_op start;		/* called on stream on after URBs creation. Can't allocate any resources here! */
 	cam_pkt_op pkt_scan;
 /* optional operations */
 	cam_op isoc_init;	/* called on stream on before getting the EP */
 	cam_op isoc_nego;	/* called when URB submit failed with NOSPC */
-	cam_v_op stopN;		/* called on stream off - main alt */
-	cam_v_op stop0;		/* called on stream off & disconnect - alt 0 */
+	cam_v_op stopN;		/* called on stream off, only if usb device is present - main alt */
+	cam_v_op stop0;		/* called on stream off, only if usb device is present - alt 0 */
 	cam_v_op dq_callback;	/* called when a frame has been dequeued */
 	cam_get_jpg_op get_jcomp;
 	cam_set_jpg_op set_jcomp;
-- 
2.20.1