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

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Date:   Wed, 1 Feb 2017 01:13:49 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Steve Longerbeam <slongerbeam@...il.com>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>, robh+dt@...nel.org,
        mark.rutland@....com, shawnguo@...nel.org, kernel@...gutronix.de,
        fabio.estevam@....com, mchehab@...nel.org, hverkuil@...all.nl,
        nick@...anahar.org, markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, bparrot@...com,
        geert@...ux-m68k.org, arnd@...db.de, sudipm.mukherjee@...il.com,
        minghsiu.tsai@...iatek.com, tiffany.lin@...iatek.com,
        jean-christophe.trotin@...com, horms+renesas@...ge.net.au,
        niklas.soderlund+renesas@...natech.se, robert.jarzmik@...e.fr,
        songjun.wu@...rochip.com, andrew-ct.chen@...iatek.com,
        gregkh@...uxfoundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev
 driver

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.

-- 
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