[Patch 2/4] dt-bindings: display/ti: Add plane binding to dispc node

[Rob Herring]

On Wed, Mar 14, 2018 at 6:23 AM, Tomi Valkeinen <tomi.valkeinen at ti.com> wrote:
> On 09/03/18 20:27, Benoit Parrot wrote:
>
>>> Is logical plane a h/w concept?
>>
>> It does represent a hardware resource.
>
> Logical plane is not a hw concept, it just describes a group of one or
> two HW planes. Then again, in the context of 2k+ displays, two HW planes
> must always be used together, so that way it could be considered a
> single HW resource.
>
>>> Really, I'm skeptical that any of this belongs in DT. For example,
>>> can't you figure out you need 2 physical planes whenever your
>>> panel/timing width is greater than 2048?
>>
>> As stated in the description I added above, we cannot have resources
>> exposed to user-space which can "disappear" dynamically.
>> Doing so would break user-space applications which rely on these
>> resources.

Isn't this the point of atomic mode setting? If you have 2 planes
free, then you can support the mode, otherwise you fail. How would a
plane be in use if you are doing modesetting unless it is on another
display?

> The question is, if not in DT, then where? I agree that this is not
> exactly describing the HW. But it can't be done dynamically either (or
> at least we have not figured out a way). And it must be user configurable.

If you are plugging in a monitor, doesn't it have to be dynamic?

> Module parameters are an option, but it would be somewhat difficult to
> give all this information there. And also, if your board has a 2k+
> display, you must have these configurations given to the driver, it's
> not optional.

Can't you look at the panel size on boot or module load and determine
if you need to combine planes or not. The main difference I see is
that the driver would have to figure out which planes to use rather
than DT telling it what planes to use. Is deciding which planes a hard
problem?

>
> And while it's perhaps stretching the definitions a bit, I guess one
> could argue that this describes the HW in a way: it describes how the HW
> resources must be used if you have a display of 2k+ width, and is not as
> such related to Linux or DRM.
>
>  Tomi
>
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