[RFC 0/1] drm: Add Grain Media GM12U320 kms driver

[Noralf Trønnes]

Den 07.06.2017 21.50, skrev Marco Diego Aurélio Mesquita:
> On Wed, Jun 7, 2017 at 4:38 PM, Noralf Trønnes <noralf at tronnes.org> wrote:
>> Den 07.06.2017 20.46, skrev Marco Diego Aurélio Mesquita:
>>> Hi Noralf!
>>>
>>> On Wed, Jun 7, 2017 at 1:56 PM, Noralf Trønnes <noralf at tronnes.org> wrote:
>>>> tinydrm is targeted at displays on slow busses where userspace tells
>>>> the driver which part of the framebuffer it has changed to minimize
>>>> the transfer.
>>>>
>>>> The PL111 driver uses drm_simple_display_pipe and might be a better
>>>> example for your use case:
>>>> https://cgit.freedesktop.org/drm/drm-misc/tree/drivers/gpu/drm/pl111
>>> I'll investigate how to modify the pl111 driver to fit my needs then.
>>> Do you think is there any change that must be done to the
>>> pl111_get_panel function regarding the call to
>>> of_graph_get_next_endpoint? I mean, the udl driver (which the gm12u320
>>> driver is based on) does not have a panel; would any change be needed
>>> because of this?
>>
>> I guess you can keep your get_modes and do something like this:
>>
>> static const struct drm_connector_helper_funcs gm12u320_helper_funcs = {
>>      .get_modes = gm12u320_get_modes,
>> };
>>
>> .best_encoder has a default that fits your 1 encoder case.
>>
>> static const struct drm_connector_funcs gm12u320_connector_funcs = {
>>      .fill_modes = drm_helper_probe_single_connector_modes,
>>      .destroy = gm12u320_connector_destroy,
>>      .detect = gm12u320_detect,
>>      .dpms = drm_atomic_helper_connector_dpms,
>>      .reset = drm_atomic_helper_connector_reset,
>>      .atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
>>      .atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
>> };
>>
>> Then you init and add helper:
>>      drm_connector_init(dev, connector, &gm12u320_connector_funcs,
>>                 DRM_MODE_CONNECTOR_Unknown);
>>      drm_connector_helper_add(connector, &gm12u320_helper_funcs);
>>
>> And finally attach the connector to the pipe:
>>      drm_simple_display_pipe_init(..., connector);
>>
>> The connector is registered when the drm device is registered.
>>
> Thanks Noralf! That's exactly what I did and I'll test it soon. The
> parts that scare me the most are the calls to
> of_graph_get_next_endpoint, of_property_read_u32_array and of_node_put
> (in display.c, for example). I'm still not sure those will work.

You don't need those since you don't have a panel nor those pads:
https://cgit.freedesktop.org/drm/drm-misc/tree/Documentation/devicetree/bindings/display/arm,pl11x.txt

The reason I pointed you to the PL111 driver is because it's very simple,
so it's easy to see how the simple pipeline works.
It uses CMA memory and if you can use that all is well, but if you need
to access the framebuffer from the cpu, it's not so good, because cma
memory has uncached reads.
The udl driver handles memory in a different way.

I'm out of my depths here with memory and GEM and stuff.

Noralf.