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author | Sakari Ailus <sakari.ailus@linux.intel.com> | 2021-06-23 14:38:31 +0200 |
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committer | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2021-08-04 14:43:50 +0200 |
commit | 013c35b22e6216b0bde04a1fc3a1a4b599a4e13f (patch) | |
tree | f268fe89a8188bbef404bae22b92b0b2f08e4776 /Documentation/driver-api | |
parent | e5a466d4bcf962daa8fea589b09a5675bda275a1 (diff) | |
download | linux-stable-013c35b22e6216b0bde04a1fc3a1a4b599a4e13f.tar.gz linux-stable-013c35b22e6216b0bde04a1fc3a1a4b599a4e13f.tar.bz2 linux-stable-013c35b22e6216b0bde04a1fc3a1a4b599a4e13f.zip |
media: Documentation: v4l: Rework LP-11 documentation, add callbacks
Rework LP-11 and LP-111 mode documentation to make it more understandable
and useful. This involves adding pre_streamon and post_streamon callbacks
that make it possible to explicitly transition the transmitter to either
mode.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Diffstat (limited to 'Documentation/driver-api')
-rw-r--r-- | Documentation/driver-api/media/tx-rx.rst | 40 |
1 files changed, 28 insertions, 12 deletions
diff --git a/Documentation/driver-api/media/tx-rx.rst b/Documentation/driver-api/media/tx-rx.rst index 12d492d25df2..e1e9258dd862 100644 --- a/Documentation/driver-api/media/tx-rx.rst +++ b/Documentation/driver-api/media/tx-rx.rst @@ -93,18 +93,34 @@ where LP-11 and LP-111 modes ^^^^^^^^^^^^^^^^^^^^^^ -The transmitter drivers must, if possible, configure the CSI-2 transmitter to -*LP-11 or LP-111 mode* whenever the transmitter is powered on but not active, -and maintain *LP-11 or LP-111 mode* until stream on. Only at stream on time -should the transmitter activate the clock on the clock lane and transition to -*HS mode*. - -Some transmitters do this automatically but some have to be explicitly -programmed to do so, and some are unable to do so altogether due to -hardware constraints. - -The receiver thus need to be configured to expect LP-11 or LP-111 mode from the -transmitter before the transmitter driver's ``.s_stream()`` op is called. +As part of transitioning to high speed mode, a CSI-2 transmitter typically +briefly sets the bus to LP-11 or LP-111 state, depending on the PHY. This period +may be as short as 100 µs, during which the receiver observes this state and +proceeds its own part of high speed mode transition. + +Most receivers are capable of autonomously handling this once the software has +configured them to do so, but there are receivers which require software +involvement in observing LP-11 or LP-111 state. 100 µs is a brief period to hit +in software, especially when there is no interrupt telling something is +happening. + +One way to address this is to configure the transmitter side explicitly to LP-11 +or LP-111 mode, which requires support from the transmitter hardware. This is +not universally available. Many devices return to this state once streaming is +stopped while the state after power-on is LP-00 or LP-000. + +The ``.pre_streamon()`` callback may be used to prepare a transmitter for +transitioning to streaming state, but not yet start streaming. Similarly, the +``.post_streamoff()`` callback is used to undo what was done by the +``.pre_streamon()`` callback. The caller of ``.pre_streamon()`` is thus required +to call ``.post_streamoff()`` for each successful call of ``.pre_streamon()``. + +In the context of CSI-2, the ``.pre_streamon()`` callback is used to transition +the transmitter to the LP-11 or LP-111 mode. This also requires powering on the +device, so this should be only done when it is needed. + +Receiver drivers that do not need explicit LP-11 or LP-111 mode setup are waived +from calling the two callbacks. Stopping the transmitter ^^^^^^^^^^^^^^^^^^^^^^^^ |