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Subject: Re: [PATCH 2/3] [media] tc358743: Increase FIFO level to 300.
From: Philipp Zabel <p.zabel@pengutronix.de>
To: Hans Verkuil <hansverk@cisco.com>,
        Sakari Ailus <sakari.ailus@iki.fi>
Cc: Dave Stevenson <dave.stevenson@raspberrypi.org>,
        Mauro Carvalho Chehab <mchehab@s-opensource.com>,
        Mats Randgaard <matrandg@cisco.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hans.verkuil@cisco.com>,
        linux-media@vger.kernel.org,
        Sakari Ailus <sakari.ailus@linux.intel.com>
Date: Thu, 21 Sep 2017 11:04:40 +0200
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Hi Hans,

On Wed, 2017-09-20 at 15:12 +0200, Hans Verkuil wrote:
[...]
> I don't like it :-)
> 
> Currently g_mbus_config returns (and I quote from v4l2-mediabus.h): "How
> many lanes the client can use". I.e. the capabilities of the HW.
> 
> If we are going to use this to communicate how many lines are currently
> in use, then I would propose that we add a lane mask, i.e. something like
> this:
> 
> /* Number of lanes in use, 0 == use all available lanes (default) */
> #define V4L2_MBUS_CSI2_LANE_MASK                (3 << 10)
> 
> And add comments along the lines that this is a temporary fix.
> 
> I would feel a lot happier (or a lot less unhappy) if we'd do it this way.
> Rather than re-interpreting bits that are not quite what they should be.
> 
> I'd also add a comment that all other flags must be 0 if the device tree is
> used. This to avoid mixing the two.

I would like to try this.

Currently the driver sets the V4L2_MBUS_CSI2_[1-4]_LANE bits according
to csi_lanes_in_use, which is wrong as you say.

After moving the csi_lanes_in_use info into a new
V4L2_MBUS_CSI2_LANE_MASK bitfield, the V4L2_MBUS_CSI2_[1-4]_LANE bits
could be either set to zero or to the really connected lanes as
configured in the device tree (csi->bus.num_data_lanes) in the DT case.

What would the bits be set to in the pdata case, though? Should a lane
count setting be added to tc358743_platform_data with, defaulting to all
bits set?

regards
Philipp