[PATCH v2 2/3] ARM: dts: imx6qdl-wandboard: Add HDMI support

[s.hauer@pengutronix.de (Sascha Hauer)]

On Tue, Oct 15, 2013 at 11:35:00AM +0100, Russell King - ARM Linux wrote:
> On Tue, Oct 15, 2013 at 10:18:30AM +0100, Russell King - ARM Linux wrote:
> > On Tue, Oct 15, 2013 at 09:46:18AM +0200, Sascha Hauer wrote:
> > > This sounds like the wrong clock polarity. Could you try inverting
> > > sig_cfg.clk_pol in imx-drm/ipuv3-crtc.c?
> > 
> > I tweaked it a different way - I used devmem2 to directly poke at the
> > register.  Inverting bit 17 (iow, clearing it) seems to fix the
> > problem.
> 
> As a follow-up, the driver says this:
> 
>         unsigned clk_pol:1;     /* true = rising edge */
> 
> This is interpreted by the ipu-di.c driver as:
> 
>         if (!sig->clk_pol)
>                 di_gen |= DI_GEN_POLARITY_DISP_CLK;
> 
> note the inversion.  U-boot does something slightly different here
> (apparantly it describes clk_pol in the same way though):
> 
>                 if (sig.clk_pol)
>                         di_gen |= DI_GEN_POL_CLK;
> 
> It's also reported that u-boot sets sig.clk_pol when
> FB_SYNC_CLK_LAT_FALL bit is not set (which confirms that clk_pol
> indicates rising edge active.)
> 
> Now, the confusing bit.  The docs for the imx6s/dl say that bit 17
> when set is "active high" vs clear "active low".  This appears to
> define a level active state.  The code seems to define an edge
> instead.  What's more is that u-boot and the kernel seem to describe
> 'clk_pol' in the same way yet interpret it differently.
> 
> Should that inversion in the kernel be there?

I could measure the pin with an oscilloscope on some board using
the parallel display output. That should how this bit really behaves
and we can cleanup the comments and/or code.

Won't have time for this before Edinburgh though.

Sascha

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