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From: Hans Petter Selasky <>
To: Linux Media Mailing List <>
Subject: [PATCH] Genesys Logic UVC microscopes used to work with Linux
Date: Sun, 6 Jun 2021 15:32:55 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>


Some USB video class compliant devices, like Genesys Logic camera chips, 
used in cheap microscopes, doesn't provide any image if there are UVC 
SET current value commands for the processing unit, before the camera 
stream is activated. Fix this by not issuing any UVC SET current value 
commands, if the value was not changed. This should also work fine with 
existing UVC compliant webcams and optimized the number of needed 
processing unit control endpoint requests.

Signed-off-by: Hans Petter Selasky <>

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c 
index b3dde98499f4..0d7137eca331 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -1697,7 +1697,13 @@ int uvc_ctrl_set(struct uvc_fh *handle,
         if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS)
                 ctrl->handle = handle;

-       ctrl->dirty = 1;
+       /* Avoid setting the current value. */
+       if (!ctrl->dirty &&
+           memcmp(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_BACKUP),
+                  uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
+                  ctrl->info.size) != 0)
+               ctrl->dirty = 1;
         ctrl->modified = 1;
         return 0;

  reply	other threads:[~2021-06-06 13:34 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-05 21:32 Genesys Logic UVC microscopes used to work with Linux, but no longer do Hans Petter Selasky
2021-06-06 13:32 ` Hans Petter Selasky [this message]
2021-06-07 20:17   ` [PATCH] Genesys Logic UVC microscopes used to work with Linux Ricardo Ribalda Delgado
2021-06-07 22:29     ` Laurent Pinchart
2021-06-06 19:41 ` Genesys Logic UVC microscopes used to work with Linux, but no longer do Ricardo Ribalda Delgado
2021-06-07 13:09   ` Hans Petter Selasky

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