linux-kernel - [PATCH v2 RESEND] media: uvcvideo: uvc_ctrl_get_rel

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Date:   Mon, 20 Nov 2023 19:47:51 +0100
From:   Gergo Koteles <soyer@....hu>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Gergo Koteles <soyer@....hu>
Subject: [PATCH v2 RESEND] media: uvcvideo: uvc_ctrl_get_rel_speed: use 0 as default

Devices with pan/tilt controls but without pan/tilt speed controls
return 1 for the default value of V4L2_CID_PAN_SPEED or
V4L2_CID_TILT_SPEED. For these controls, the value of 1 means a
move and that's not a good default.

Currently, for these controls the UVC_GET_DEF query returns
bPanSpeed or bTiltSpeed of CT_PANTILT_RELATIVE_CONTROL.

According to the UVC 1.5 specification, the default value of bPanSpeed
or bTiltSpeed should be 1 if the pan/tilt control doesn't support
speed control.

"If the control does not support speed control for the Tilt control,
it will return the value 1 in this field for all these requests."

This patch modifies the uvc_ctrl_get_rel_speed to return hardcoded 0
for UVC_GET_DEF query, because that's the stop or don't move value
for these V4L2 controls.

Previous discussion
Link: https://lore.kernel.org/all/CAP_ceTy6XVmvTTAmvCp1YU2wxHwXqnarm69Yaz8K4FmpJqYxAg@mail.gmail.com/

Signed-off-by: Gergo Koteles <soyer@....hu>
---
 drivers/media/usb/uvc/uvc_ctrl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 5e9d3da862dd..e131958c0930 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -444,9 +444,10 @@ static s32 uvc_ctrl_get_rel_speed(struct uvc_control_mapping *mapping,
 		return -data[first+1];
 	case UVC_GET_MAX:
 	case UVC_GET_RES:
+		return data[first+1];
 	case UVC_GET_DEF:
 	default:
-		return data[first+1];
+		return 0;
 	}
 }

base-commit: be9aac187433af6abba5fcc2e73d91d0794ba360
-- 
2.42.0