Re: [RFC PATCH] dt-bindings: display: ti,tfp410.txt: convert to yaml

["Ricardo Cañuelo" <ricardo.canuelo@collabora.com>]

Hi Laurent,

On mié 06-05-2020 18:53:20, Laurent Pinchart wrote:
> I didn't if I remember correctly, I just mapped it to the hardware
> features. The hardware register indeed takes a value between 0 and 7,
> and that is mapped to [-4,3] x t(STEP). I don't mind either option.

I was taking a look at the ti-tfp410.c driver to see if it needs any
changes to support the updated deskew property ranges [0-7], but I don't
fully understand what this does (line 276):

	/* Get the setup and hold time from vendor-specific properties. */
	of_property_read_u32(dvi->dev->of_node, "ti,deskew", (u32 *)&deskew);
	if (deskew < -4 || deskew > 3)
		return -EINVAL;

	timings->setup_time_ps = min(0, 1200 - 350 * deskew);
	timings->hold_time_ps = min(0, 1300 + 350 * deskew);

It looks like that the driver doesn't really apply the deskew settings
to the device and that this has not been really tested, so it's probably
not a big deal.

I guess what you wanted to do was to adjust the setup and hold times
around 1200 and 1300 ps respectively in increments/decrements of 350 ps
depending on the deskew value, as the datasheet describes. But this code
would set timings->setup_time_ps to 0 regardless of the deskew value,
and timings->hold_time_ps would be either 0 or a very big integer value
if deskew is -4 (both setup_time_ps and hold_time_ps are u32).

Am I missing something? Was this intentional?

Thanks,
Ricardo