Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev driver

From	Russell King - ARM Linux <linux@armlinux.org.uk>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev driver
Date	2017-02-01 02:20 +0100
Message-ID	<t5RKx-7Qx-5@gated-at.bofh.it> (permalink)
References	<sWOLT-2qI-3@gated-at.bofh.it> <sWOLU-2qI-53@gated-at.bofh.it> <t5ubg-28G-13@gated-at.bofh.it> <t5Doe-7zo-15@gated-at.bofh.it> <t5RAR-7Nm-13@gated-at.bofh.it>
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Hi Steve,

On Tue, Jan 31, 2017 at 05:02:40PM -0800, Steve Longerbeam wrote:
> But this also puts a requirement on MIPI sensors that s_power(ON)
> should only place the D_PHY in LP-11, and _not_ start the clock lane.
> But perhaps that is correct behavior anyway.

If the CSI2 DPHY is held in reset state, it shouldn't matter what the
sensor does.  In the case of IMX219, it needs a full setup of the
device, including enabling it to stream (so it starts the clock lane
etc) in order to get it into LP-11 state.  Merely disabling the XCLR
signal leaves the lanes grounded.

I do seem to remember reading in one of the MIPI specs that this is
rather expected behaviour, though I can't point at a paragraph this
late in the night.

So, the only way to satisfy these requirements is this order:

- assert PHY reset signals (so blocking any activity on the CSI lanes)
- initialise the sensor (including allowing it to start streaming and
  then stopping the stream - at that point, the lanes will be in LP-11.)
- deassert the resets as per the iMX6 documentation and follow the
  remaining procedure.

I'll look at your other points tomorrow.

Thanks.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev  driver Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-01-31 01:10 +0100
  Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev  driver Philipp Zabel <p.zabel@pengutronix.de> - 2017-01-31 11:00 +0100
    Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev  driver Steve Longerbeam <slongerbeam@gmail.com> - 2017-02-01 02:10 +0100
      Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev  driver Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-02-01 02:20 +0100

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