[PATCH 2/2] RFC: drm/pl111: Support using the VGA bridge as fallback

[Daniel Vetter]

On Tue, Sep 5, 2017 at 9:43 PM, Eric Anholt <eric at anholt.net> wrote:
> Daniel Vetter <daniel at ffwll.ch> writes:
>
>> On Fri, Sep 01, 2017 at 11:46:29AM +0200, Linus Walleij wrote:
>>> If we cannot find a panel, assume that the output from the
>>> PL111 is connected directly to a "dumb" VGA connector,
>>> so look up the connector from that bridge.
>>>
>>> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
>>> ---
>>> This is how the new API is used in the PL111.
>>> ---
>>>  drivers/gpu/drm/pl111/Kconfig     | 1 +
>>>  drivers/gpu/drm/pl111/pl111_drv.c | 3 +++
>>>  2 files changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/pl111/Kconfig b/drivers/gpu/drm/pl111/Kconfig
>>> index e5e2abd66491..82cb3e60ddc8 100644
>>> --- a/drivers/gpu/drm/pl111/Kconfig
>>> +++ b/drivers/gpu/drm/pl111/Kconfig
>>> @@ -8,6 +8,7 @@ config DRM_PL111
>>>      select DRM_GEM_CMA_HELPER
>>>      select DRM_BRIDGE
>>>      select DRM_PANEL_BRIDGE
>>> +    select DRM_DUMB_VGA_DAC
>>>      select VT_HW_CONSOLE_BINDING if FRAMEBUFFER_CONSOLE
>>>      help
>>>        Choose this option for DRM support for the PL111 CLCD controller.
>>> diff --git a/drivers/gpu/drm/pl111/pl111_drv.c b/drivers/gpu/drm/pl111/pl111_drv.c
>>> index f5bc6f160e60..6db423bbd84e 100644
>>> --- a/drivers/gpu/drm/pl111/pl111_drv.c
>>> +++ b/drivers/gpu/drm/pl111/pl111_drv.c
>>> @@ -67,6 +67,7 @@
>>>  #include <drm/drm_of.h>
>>>  #include <drm/drm_bridge.h>
>>>  #include <drm/drm_panel.h>
>>> +#include <drm/dumb_vga_dac.h>
>>>
>>>  #include "pl111_drm.h"
>>>  #include "pl111_versatile.h"
>>> @@ -128,6 +129,8 @@ static int pl111_modeset_init(struct drm_device *dev)
>>>      if (panel) {
>>>              priv->panel = panel;
>>>              priv->connector = panel->connector;
>>> +    } else {
>>> +            priv->connector = drm_dumb_vga_get_connector(bridge);
>>
>> Why do you need to set this? The only code I could find tries to set
>> polarity values from bus_flags, and for VGA I'd assume you want to instead
>> key this off the mode?
>>
>> Wrt the more general problem: They way we solve this in the i915 atomic
>> framework is that the various ->fixup calls fill out relevant fields in
>> the drm_crtc_state. I guess we could add an ->atomic_check to bridges, add
>> a bus_flags to drm_crtc_state (or maybe just let everyone patch up
>> adjusted_mode->flags) instead?
>
> It seems to me like the bus_flags/format should be specific to each link
> in the display output chain, rather than global to it.

Yeah that might be the even more general option, to have a
drm_bridge_state for this stuff. Thanks to the driver private state
support recently added you can add state pointers for any void * (and
with a bit of glue even set up type-safe duplicate/get/for_each
wrappers). But I'm not clear whether we really need that much
generality or not. Currently it's used for the intel shared dpll stuff
and the dp mst state, in case someone needs to dig for examples.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch