Re: [PATCH 3/6] ARM: dts: da850-lcdk: enable the LCD controller

From: Bartosz Golaszewski
Date: Fri Sep 30 2016 - 05:42:27 EST

2016-09-29 20:40 GMT+02:00 Karl Beldan <karl.beldan@xxxxxxxxx>:
> Hi,
> On Thu, Sep 29, 2016 at 06:31:52PM +0200, Bartosz Golaszewski wrote:
>> From: Karl Beldan <kbeldan@xxxxxxxxxxxx>
>> This adds the pins used by the LCD controller, and uses 'tilcdc,panel'
>> with some default timings for 800x600.
>> Tested on an LCDK connected on the VGA port (the LCDC is connected to
>> this port via a THS8135).
>> Signed-off-by: Karl Beldan <kbeldan@xxxxxxxxxxxx>
>> [Bartosz:
>> - fixed whitespace errors
>> - tweaked the description
> The description tweak you mention is the removal of an erratum which is
> in the mentioned commit I put on github @
> (
> it included an erratum wrt FIFO threshold I think is worth keeping:
> {
> There is an erratum (fifo-th) "LCDC: Underflow During Initialization":
> [...]
> "This problem may occur if the LCDC FIFO threshold size (
> LCDDMA_CTRL[TH_FIFO_READY]) is left at its default value after reset.
> Increasing the FIFO threshold size will reduce or eliminate underflows.
> Setting the threshold size to 256 double words or larger is
> recommended."
> }

Isn't this the issue that is fixed by changing the memory priority for lcdc?

>> - fixed the incorrect hback-porch value
> It can't be a fix, this value depends on the monitor connected.

Thanks, I'm new to drm. From reading the datasheet it seemed to me
that this depends on the resolution. FWIW it seems that most LCDs are
able to adjust to this themselves - I tested with two different
displays and the value I introduced worked on both while the previous
one shifted the image to the right. I'll look into that.

>> - other minor tweaks]
> I didn't see any other change while diffing.

Dropped the refresh rate from the timings node name.