Hi Boris,

On Wednesday 27 August 2014 09:52:35 Boris BREZILLON wrote:

On Tue, 26 Aug 2014 01:39:21 +0200 Laurent Pinchart wrote:

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On Thursday 21 August 2014 19:26:33 Boris BREZILLON wrote:

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On Thu, 21 Aug 2014 19:08:53 +0200
Laurent Pinchart [off-list ref] wrote:

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While this could be acceptable when all drivers are statically
linked in the kernel, it might be problematic when you're using
modules, meaning that you won't be able to display anything on your
LCD panel until your HDMI bridge module has been loaded.

No. HDMI should be using proper hotplugging anyway, hence it should
be always be loaded anyway. You're in for a world of pain if you
think you can run DRM with a driver that's composed of separate
kernel modules.

I was talking about the external RGB to HDMI encoder, should the
driver for this encoder (which is not on On Chip block) be compiled
statically too ?

Given the move to multiplatform kernels we need to aim for as few
modules compiled in as possible. I'd say this includes HDMI encoders,
panels and display controllers.

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Also if you don't want to use deferred probe, then you're in for the
full hotplugging panel dance and that implies that you need to fix a
bunch of things in DRM (one being the framebuffer console
instantiation that I referred to in the other thread).

For now, I wait until there is a device connected on the RGB
connector (connector status set to connector_status_connected) before
creating an fbdev. It might not be the cleanest way to solve this
issue, but it works :-).

Do you create a new drm_encoder at runtime for the HDMI encoder when
it appears ? I thought the DRM core and API were not able to correctly
cope with that.

I haven't started to work on the HDMI encoder yet, and ATM I only have
a single connector (which is true from an HW POV), which is then bound
to an LCD panel (the only type of remote endpoint I currently support).

BTW, I wonder how my use case should be represented in the DRM
subsystem. As I said, from an HW POV I only have one RGB (or whatever
name you choose for it) connector. But on such kind of connectors you
can connect several output devices (panels, encoders, ...).
And in my case I have 2 devices on the same RGB connector: a panel and
an RGB to HDMI converter.

The DRM connector object was initially meant to model a physical user-
accessible connector on a board (VGA, DVI, HDMI, ...) and the properties
of the monitor plugged into it. It has then been (ab)used to represent
panels, as they're similar to monitors.

In your case the VGA and HDMI connectors should be modeled as DRM
connectors, the RGB to HDMI encoder as a DRM encoder, and the LCDC as a
DRM CRTC.

I don't have any VGA connector (or I'm missing something :-)),

My bad.

but I have an LCD panel and an RGB to HDMI encoder connected on the same RGB
connector.

There's no such thing as an RGB connector in DRM. Your SoC has a parallel RGB 
video output (I assume it's a DPI bus). From a DRM point of view, that bus 
corresponds to the output of the CRTC.

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As DRM hardcodes the pipeline model to CRTC -> encoder -> connector, you
will also need a DRM encoder in the VGA path. I suppose your board has a
VGA DAC, that's the component you should expose as a DRM encoder (even if
it can't be controlled and doesn't limit the valid modes).

Actually, my problem is that both devices are connected on the same RGB
connector, and thus share the same display mode (resolution, HSYNC,
VSYNC, RGB output mode, ...).
This means that all remote devices have to agree on a specific mode if
we want to mirror the display on several output devices, otherwise we
must disable one of the output devices.

That's not really a problem. From a DRM perspective you need to model your 
device as

,------.       ,---------------.       ,-----------------.
| CRTC | -+--> | Dummy Encoder | ----> | Panel Connector |
`------´  |    `---------------´       `-----------------´
          |    ,---------------.       ,-----------------.
          \--> | HDMI Encoder  | ----> | HDMI Connector  |
               `---------------´       `-----------------´

The HDMI pipeline is pretty straightforward.

You have told me that the panel has a parallel RGB input without any encoder 
in the panel pipeline (by the way, which panel model are you using ?). 
However, DRM requires an encoder in every pipeline. You will thus need to 
instantiate a dummy encoder. One option would be to set the encoder and 
connector types to DRM_MODE_ENCODER_LVDS and DRM_MODE_CONNECTOR_LVDS 
respectively, as that's what userspace usually expects for panels. That 
doesn't reflect the reality in your case though, so creating a new 
DRM_MODE_CONNECTOR_DPI type might be needed, possibly to be used with 
DRM_MODE_ENCODER_NONE.

As neither encoder can modify the mode, the same mode will be output on the 
two connectors.

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You also can't be using the current device tree bindings because
they all assume a dependency from the display controller/output to
the panel. For hotplugging you'd need the dependency the other way
around (the panel needs to refer to the output by phandle).

Here [1] is a proposal for notification support in the drm_panel
infrastructure (which is not that complicated), and here [2] is how
I use it in my atmel-hlcdc driver to generate hotplug events.

Is there a way we could use the component framework for that ? I know
that partial notification isn't supported at the moment, but Russell
agreed it was a real use case that should be implemented at some
point.

I'll give it a try.

-- 
Regards,

Laurent Pinchart