Re: [PATCH 2/2] drm/tegra: Obtain head number from DT

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 01/14/2014 07:14 AM, Thierry Reding wrote:
> On Mon, Jan 13, 2014 at 10:46:45AM -0700, Stephen Warren wrote:
>> On 01/13/2014 07:21 AM, Thierry Reding wrote:
>>> The head number of a given display controller is fixed in hardware and
>>> required to program outputs appropriately. Relying on the driver probe
>>> order to determine this number will not work, since that could yield a
>>> situation where the second head was probed first and would be assigned
>>> head number 0 instead of 1.
>>
>> This change makes the new properties mandatory, yet they aren't part of
>> the DT files yet. So, won't this patch break all display on Tegra?
> 
> I don't think it'll make anything worse than it currently is, since both
> display controllers can't run at the same time with the current code.

Sure it will; it will prevent any dc device from probing at all:

> +static int tegra_dc_parse_dt(struct tegra_dc *dc)
...
> +	err = of_property_read_u32(dc->dev->of_node, "nvidia,head", &value);
> +	if (err < 0)
 +		return err;
                ^^^^^^^^^^^
...
> @@ -1207,6 +1219,10 @@ static int tegra_dc_probe(struct platform_device *pdev)
...
> +	err = tegra_dc_parse_dt(dc);
> +	if (err < 0)
> +		return err;
                ^^^^^^^^^^^