linux-kernel - [PATCH v2 0/3] media: qcom: camss: V4L2_CID_PIXEL_RATE/LINK

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Date:   Thu, 18 Feb 2021 01:11:31 +0300
From:   Andrey Konovalov <andrey.konovalov@...aro.org>
To:     junak.pub@...il.com, robert.foss@...aro.org,
        sakari.ailus@...ux.intel.com
Cc:     todor.too@...il.com, agross@...nel.org, bjorn.andersson@...aro.org,
        mchehab@...nel.org, laurent.pinchart@...asonboard.com,
        jacopo@...ndi.org, linux-media@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/3] media: qcom: camss: V4L2_CID_PIXEL_RATE/LINK_FREQ fixes

The first patch adds printing a warning in v4l2_get_link_freq() if
V4L2_CID_LINK_FREQ isn't implemented (this is a mandatory control for
CSI-2 transmitter drivers [1], but many sensor drivers don't have it
currently).

The second patch is the start of the work discussed in the "[RFC] Repurpose
V4L2_CID_PIXEL_RATE for the sampling rate in the pixel array" thread [2].
I plan to send a few other similar patches for other CSI receiver drivers,
and if the current patchset needs to wait for those before it can be merged,
that's fine for me.

The reason I decided to post the camss patch first is the patch [3] by
Vladimir Lypak. The third patch in this series is the Vladimir's patch
rebased onto the changes done by the second patch. By replacing getting
the pixel clock with v4l2_get_link_freq() the second patch also fixes the
integer overflow which Vladimir's patch addresses. So the third patch
only needs to fix drivers/media/platform/qcom/camss/camss-vfe.c which
the second patch doesn't touch.

The resulting patchset is free from the "undefined reference to `__udivdi3'"
issue [4] as the u64 value is only divided by a power of 2, which doesn't
need do_div().

[1] https://linuxtv.org/downloads/v4l-dvb-apis-new/driver-api/csi2.html
[2] https://www.spinics.net/lists/linux-media/msg183183.html
[3] https://www.spinics.net/lists/linux-media/msg186875.html
[4] https://www.spinics.net/lists/linux-media/msg186918.html

Changes in v2:

* Added [PATCH 1/3] v4l: common: v4l2_get_link_freq: add printing a warning

* camss_get_link_freq() changed to take the actual number of lanes as the
  third arg vs the number of lanes multiplied by 2 in the first version

* Fixed checkpatch warnings and bad indentation