Add new hardware strobe signal control to v4l uAPI documentation.

Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
---
 Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
index 03a58ef94be7c870f55d5a9bb09503995dbfb402..af43e7329cb77cf952b8996cd8c5384eae08c3fc 100644
--- a/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
+++ b/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
@@ -191,3 +191,9 @@ Flash Control IDs
     Duration the flash should be on when the flash LED is in flash mode
     (V4L2_FLASH_LED_MODE_FLASH). The unit should be microseconds (µs)
     if possible.
+
+``V4L2_CID_FLASH_HW_STROBE_SIGNAL (boolean)``
+    Enable or disable the output of a hardware strobe signal. This is typically
+    set on a sensor that provides a hardware strobe output which is connected
+    to a flash device/LEDs. The flash device should then be configured to use
+    an external strobe source (V4L2_FLASH_STROBE_SOURCE_EXTERNAL).

-- 
2.47.2