linux-kernel - [PATCH 1/4] media: uvcvideo: Fix comments in uvc_meta_detect

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Message-Id: <20250818-uvc-iq-switch-v1-1-f7ea5e740ddd@chromium.org>
Date: Mon, 18 Aug 2025 20:15:36 +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>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-usb@...r.kernel.org, Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH 1/4] 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")
Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
Link: https://lore.kernel.org/r/20250716-uvc-meta-followup-v2-1-d3c2b995af3d@chromium.org
Signed-off-by: Hans de Goede <hansg@...nel.org>
---
 drivers/media/usb/uvc/uvc_metadata.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_metadata.c b/drivers/media/usb/uvc/uvc_metadata.c
index 3b0b392895119bb6ac300fc40b89a7ea00e56b40..b0960f0553cfcb30b0036d2ad8877fafa225c6a4 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 +211,11 @@ 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 reported by
+	 * GET_MAX to enable production of MSXU metadata. The GET_MAX request
+	 * reports the maximum size of the metadata, if its value is 0 then MSXU
+	 * metadata is not supported. For more information, see
+	 * 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));

-- 
2.51.0.rc1.167.g924127e9c0-goog