Re: [PATCH 6/6] drm/msm/dsi: Parse DSI lanes via DT

[Rob Herring <robh@kernel.org>]

On Tue, Feb 23, 2016 at 01:11:24PM +0200, Tomi Valkeinen wrote:
> 
> 
> On 23/02/16 12:43, Archit Taneja wrote:
> > 
> > 
> > On 02/23/2016 02:48 PM, Tomi Valkeinen wrote:
> >>
> >> On 22/02/16 22:10, Rob Herring wrote:
> >>
> >>>> If we want all DSI host controllers to use a common binding to describe
> >>>> lanes, we'd need to go with the most flexible one, and the driver
> >>>> restricts it to the subsets that we support.
> >>
> >> True, but I wonder if that's necessary. The lane property for the SoC
> >> should be read by the SoC specific driver, right? So the DT property can
> >> be anything. I'm not sure if there's ever a reason for a generic code to
> >> observe the DSI lane setup.
> > 
> > Yeah, it is very SoC specific.

Agreed.

> > The only place where it might matter is if a panel/bridge ever needs to
> > know what pins implement what lanes on the platform. A common binding
> > there might help us keep the panel driver generic. Although, this need
> > itself is a bit hypothetical.
> 
> My opinion here is that if the panel/bridge needs to know something
> about the DSI lanes/pins, we should have that data in the
> panel's/bridge's endpoint data.
> 
> So if both SoC and the DSI peripheral need complex DSI pin/lane setup,
> you might have very similar data on both sides. There's possibly some
> duplication there, but I think it keeps things much simpler.
> 
> For example, if the SoC needs OMAP style DSI pin data, and the DSI
> peripheral needs to know the amount of DSI lanes used (but nothing
> else), you might think it's nice if the DSI peripheral would peek at the
> SoC side data, finding out about the DSI lanes.
> 
> But I think in that case you should just add a "num-lanes" property to
> the DSI peripheral. The DT data for a device should be private to the
> driver handling the device, except for some special cases like following
> the graph.

num-lanes might not be enough. You could need to have a mask instead. 
Not sure if there is really any h/w like that though.

Also, I think it is fine for a parent to look at standard properties in 
a child.

Rob