linux-kernel - [PATCH] media: uvcvideo: Fix comments in uvc_meta_detect

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Message-Id: <20250714-uvc-meta-followup-v1-1-67bd2dc05ef2@chromium.org>
Date: Mon, 14 Jul 2025 16:45:43 +0000
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Hans de Goede <hansg@...nel.org>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Hans Verkuil <hverkuil@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH] media: uvcvideo: Fix comments in uvc_meta_detect_msxu

The comments can be more precise. Let's fix them.

Fixes: 6cb786f040ad ("media: uvcvideo: Auto-set UVC_QUIRK_MSXU_META")
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
This series fixes the uvc metadata series landed in:
https://patchwork.linuxtv.org/project/linux-media/patch/998c5fb0-8d32-496c-a1e2-cc9c1a73ede0@kernel.org/

There is no need to Cc: stable, because the series have not landed in
any stable kernel.
---
 drivers/media/usb/uvc/uvc_metadata.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_metadata.c b/drivers/media/usb/uvc/uvc_metadata.c
index 229e08ff323eed9129d835b24ea2e8085bb713b8..2905e46514d74cee09215d86e8eb7ad6e787ece1 100644
--- a/drivers/media/usb/uvc/uvc_metadata.c
+++ b/drivers/media/usb/uvc/uvc_metadata.c
@@ -196,7 +196,10 @@ static int uvc_meta_detect_msxu(struct uvc_device *dev)
 	if (!data)
 		return -ENOMEM;
 
-	/* Check if the metadata is already enabled. */
+	/*
+	 * Check if the metadata is already enabled, or if the device always
+	 * returns metadata.
+	 */
 	ret = uvc_query_ctrl(dev, UVC_GET_CUR, entity->id, dev->intfnum,
 			     MSXU_CONTROL_METADATA, data, sizeof(*data));
 	if (ret)
@@ -208,9 +211,9 @@ static int uvc_meta_detect_msxu(struct uvc_device *dev)
 	}
 
 	/*
-	 * We have seen devices that require 1 to enable the metadata, others
-	 * requiring a value != 1 and others requiring a value >1. Luckily for
-	 * us, the value from GET_MAX seems to work all the time.
+	 * Set the value of MSXU_CONTROL_METADATA to the value from GET_MAX to
+	 * enable the production of MSXU metadata.
+	 * https://learn.microsoft.com/en-us/windows-hardware/drivers/stream/uvc-extensions-1-5#2229-metadata-control
 	 */
 	ret = uvc_query_ctrl(dev, UVC_GET_MAX, entity->id, dev->intfnum,
 			     MSXU_CONTROL_METADATA, data, sizeof(*data));

---
base-commit: d968e50b5c26642754492dea23cbd3592bde62d8
change-id: 20250714-uvc-meta-followup-1ccb6e8efc2b

Best regards,
-- 
Ricardo Ribalda <ribalda@...omium.org>