Re: [PATCH 07/12] drm: drm_display_mode: add signal polarity flags

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Russell,

On Tuesday 18 March 2014 12:56:23 Russell King - ARM Linux wrote:
> On Tue, Mar 18, 2014 at 01:41:54PM +0100, Laurent Pinchart wrote:
> > Hi Lothar,
> > 
> > That's not my point. I *know* that DE is a data gating signal with a
> > polarity already defined by the DRM_MODE_FLAG_POL_DE_(LOW|HIGH) flags.
> > Like all other signals it gets generated on a clock edge and is sampled
> > on a clock edge. The DRM_MODE_FLAG_POL_DE_*EDGE flags proposed above
> > describe seem to describe just that, *not* the signal polarity. I thus
> > want to know whether there are systems where the data signals and the DE
> > signal need to be sampled on different edges of the pixel clock.
> 
> That's not relevant to this patch series though.  This patch series is
> about adding configuration which will allow iMX6 SoCs to be properly
> configured for their displays.
> 
> iMX has the ability to:
> 
> - define the polarity of the clock signal
> - define the polarity of the other signals
> 
> It does not have the ability to define which clock edge individual signals
> like vsync (frame clock), hsync (line clock), disable enable change on
> independently.
> 
> So, it doesn't make sense _here_ for the display enable to be defined by
> an edge - it's not something that can be changed here.  What can only be
> changed is it's active level.
> 
> Of course, there may be some which can do this, and that's a separate
> problem that would need to be addressed when there's hardware that does
> support it.
> 
> The objection which Lothar is raising is that _this_ definition does not
> match the _hardware_ capabilities which it is intended to be used with,
> which is a very valid objection.

Thank you for the clarification. That absolutely makes sense.

-- 
Regards,

Laurent Pinchart