Hi Boris, On Wednesday 16 July 2014 15:05:22 Boris BREZILLON wrote: > On Tue, 15 Jul 2014 13:07:58 +0200 Laurent Pinchart wrote: > > On Tuesday 15 July 2014 12:52:54 Thierry Reding wrote: > >> On Tue, Jul 15, 2014 at 12:43:02PM +0200, Laurent Pinchart wrote: > >>> On Tuesday 15 July 2014 12:37:19 Thierry Reding wrote: > >>>> On Tue, Jul 15, 2014 at 12:20:02PM +0200, Laurent Pinchart wrote: > >>>>> On Tuesday 15 July 2014 12:06:19 Boris BREZILLON wrote: > >>>>>> On Mon, 14 Jul 2014 12:05:43 +0200 Thierry Reding wrote: > >>>>>>> On Mon, Jul 07, 2014 at 06:42:59PM +0200, Boris BREZILLON wrote: > >>>>>>>> The Atmel HLCDC (HLCD Controller) IP available on some Atmel SoCs > >>>>>>>> (i.e. at91sam9n12, at91sam9x5 family or sama5d3 family) provides > >>>>>>>> a display controller device. > >>>>>>>> > >>>>>>>> The HLCDC block provides a single RGB output port, and only > >>>>>>>> supports LCD panels connection to LCD panels for now. > >>>>>>>> > >>>>>>>> The atmel,panel property link the HLCDC RGB output with the LCD > >>>>>>>> panel connected on this port (note that the HLCDC RGB connector > >>>>>>>> implementation makes use of the DRM panel framework). > >>>>>>>> > >>>>>>>> Connection to other external devices (DRM bridges) might be added > >>>>>>>> later by mean of a new atmel,xxx (atmel,bridge) property. > >>>>>>>> > >>>>>>>> Signed-off-by: Boris BREZILLON > >>>>>>>> <boris.brezillon@xxxxxxxxxxxxxxxxxx> > >>>>>>>> --- > >>>>>>>> > >>>>>>>> .../devicetree/bindings/drm/atmel-hlcdc-dc.txt | 59 ++++++++ > >>>>>>>> 1 file changed, 59 insertions(+) > >>>>>>>> create mode 100644 > >>>>>>>> Documentation/devicetree/bindings/drm/atmel-hlcdc-dc.txt > >>>>> > >>>>> [snip] > >>>>> > >>>>>>>> + - atmel,panel: Should contain a phandle with 2 parameters. > >>>>>>>> + The first cell is a phandle to a DRM panel device > >>>>>>>> + The second cell encodes the RGB mode, which can take the > >>>>>>>> following values: > >>>>>>>> + * 0: RGB444 > >>>>>>>> + * 1: RGB565 > >>>>>>>> + * 2: RGB666 > >>>>>>>> + * 3: RGB888 > >>>>>>> > >>>>>>> These are properties of the panel and should be obtained from the > >>>>>>> panel directly rather than an additional cell in this specifier. > >>>>>> > >>>>>> Okay. > >>>>>> What's the preferred way of doing this ? > >>>>>> What about defining an rgb-mode property in the panel node. > >>>>> > >>>>> You could do that, but it won't help you much, as the HLCDC driver > >>>>> must not parse properties from the panel node. You should instead > >>>>> extend the drm_panel API with a function to retrieve panel > >>>>> properties. The HLCDC driver will then query the panel driver at > >>>>> runtime for the interface type. The panel driver will get the > >>>>> information from hardcoded data in the driver, from DT or possibly > >>>>> in some cases by querying the panel hardware directly. > >>>> > >>>> My preference for this would be that we either add this to some > >>>> existing structure (struct drm_display_info seems like a good > >>>> candidate) or if the number of parameters grows out of hands, then > >>>> maybe even introduce a new type of device that's specific for the > >>>> interface. DRM panels are an abstraction for panels, that is, > >>>> interface-agnostic, and if we start exposing interface specific > >>>> parameters things will start to become very unwieldy. > >>> > >>> I agree with the goal of keeping drm_panel interface-agnostic. > >>> However, one way or another, interface parameters will need to be > >>> communicated between the panel driver and the controller driver. My > >>> preference, if we need to extend the number and/or scope of parameters > >>> beyond what drm_display_info could reasonably contain, would be to > >>> implement a new drm_panel operation to query/configure interface > >>> parameters, using a structure that contains the interface type and a > >>> union of type-specific structures. This would keep the API generic in > >>> the sense of not requiring explicit knowledge of all interfaces in the > >>> drivers, while offering the flexibility we need with a way to easily > >>> detect the interface type at runtime and react on unknown/unsupported > >>> types. > >> > >> That's exactly what I was hoping could be avoided. If instead we modeled > >> the interface type as a bus, we could for example have an lvds_bus along > >> with an lvds_device and then use that as the natural place to store > >> these properties. Much like we do for DSI. > > > > And I believe that's what we should avoid ;-) First of all, let's not > > forget that Linux models control busses, not data busses. DSI is a > > special case as it combines the control and data busses, but in the > > general case the same implementation isn't possible. An LVDS panel > > controlled through I2C needs to be an I2C device sitting on an I2C bus. > > > > Then, I believe it would make all drivers simpler if we had a single > > object type to deal with, with proper abstractions for bus types. A > > drm_panel that can model panels regardless of the data bus type, with one > > operation that conveys bus-specific information, makes storing the objects > > and communicating with them simpler than having to deal with different > > kind of devices. > > Could you detail a bit what you mean by "single object type" ? > > Is this about making a common abstraction class (by mean of > drm_xxx and drm_xxx_funcs) that could represent any display device > (drm_bridge, drm_panel, ...) ? Exactly :-) This is similar to what exists in V4L, with a v4l2_subdev object able to model any kind of IP core or external chip. I don't think we will get there in one go, but I'd like to start by merging drm_encoder and drm_bridge on the kernel side. Both objects model the same hardware, a drm_encoder on one board could be a drm_bridge on another one. >From a userspace point of view drm_encoder won't go away, and we can't chain multiple encoders, so the change would be internal to the kernel only. Then, as a next step, I believe using the same object to model panels would be a good idea, but there's no consensus on that. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
