[PATCH 1/3] media: Documentation: Document how link frequencies can be chosen

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Document how link frequencies can be selected for the link-frequencies
property.

Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
 Documentation/driver-api/media/camera-sensor.rst   | 14 ++++++++++++++
 .../userspace-api/media/drivers/camera-sensor.rst  |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst
index 6456145f96ed..0de5c86cbd1f 100644
--- a/Documentation/driver-api/media/camera-sensor.rst
+++ b/Documentation/driver-api/media/camera-sensor.rst
@@ -29,6 +29,20 @@ used in the system. Using another frequency may cause harmful effects
 elsewhere. Therefore only the pre-determined frequencies are configurable by the
 user.
 
+On choosing link frequencies
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Choosing link frequencies for a board is generally a part of the hardware design
+process as one needs to ensure an EMC-safe frequency the sensor supports with
+the given external clock frequency exists. On development systems this may be
+less than an immediate concern, so more or less anything that sensor and the
+rest of the applicable hardware supports can be used.
+
+If the sensor's PLL tree is not documented and all that is available are
+register lists, even knowing the frequency a driver uses may be difficult. This
+could still be :ref:`calculated from the number of lanes, sensor's output image
+size, blanking values and frame rate <media_camera_raw_frame_interval>`.
+
 ACPI
 ~~~~
 
diff --git a/Documentation/userspace-api/media/drivers/camera-sensor.rst b/Documentation/userspace-api/media/drivers/camera-sensor.rst
index 919a50e8b9d9..7ffed5c2338c 100644
--- a/Documentation/userspace-api/media/drivers/camera-sensor.rst
+++ b/Documentation/userspace-api/media/drivers/camera-sensor.rst
@@ -54,6 +54,8 @@ less all modern raw camera sensors.
 
 The frame interval is calculated using the following equation::
 
+.. _media_camera_raw_frame_interval:
+
 	frame interval = (analogue crop width + horizontal blanking) *
 			 (analogue crop height + vertical blanking) / pixel rate
 
-- 
2.39.2




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