Re: [PATCH v3] drm: Renesas R-Car Display Unit DRM driver

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jun 19, 2013 at 01:45:45AM +0200, Laurent Pinchart wrote:
> Hello Adam,
> 
> Ping ?
> 
> Daniel, would it help getting the driver in v3.11 if I resubmit it now with a 
> get_modes operation that just returns 0 ?

Yeah, I guess that works, too.
-Daniel

> 
> On Friday 14 June 2013 16:03:19 Daniel Vetter wrote:
> > On Fri, Jun 14, 2013 at 02:54:04AM +0200, Laurent Pinchart wrote:
> > > On Friday 07 June 2013 10:50:55 Daniel Vetter wrote:
> > > > On Fri, Jun 07, 2013 at 09:44:45AM +0200, Laurent Pinchart wrote:
> > > > > On Wednesday 05 June 2013 10:55:05 Daniel Vetter wrote:
> > > > > > On Wed, Jun 05, 2013 at 03:51:53AM +0200, Laurent Pinchart wrote:
> > > > > > > On Tuesday 04 June 2013 20:36:20 Daniel Vetter wrote:
> > > > > > > > On Tue, Jun 4, 2013 at 8:03 PM, Laurent Pinchart wrote:
> > > > > > > > > On Tuesday 04 June 2013 16:12:36 Daniel Vetter wrote:
> > > > > > > > >> On Tue, Jun 04, 2013 at 04:53:40AM +0200, Laurent Pinchart 
> wrote:
> > > > > > [snip]
> > > > > > 
> > > > > > > > >> > +static int rcar_du_vga_connector_get_modes(struct
> > > > > > > > >> > drm_connector
> > > > > > > > >> > *connector)
> > > > > > > > >> > +{
> > > > > > > > >> > +   return drm_add_modes_noedid(connector, 1280, 768);
> > > > > > > > >> > +}
> > > > > > > > >> 
> > > > > > > > >> This (and the dummy detect function below) looks a bit funny,
> > > > > > > > >> since it essentially overrides the default behaviour already
> > > > > > > > >> provided by the crtc helpers. Until rcar has at least proper
> > > > > > > > >> detect support for VGA
> > > > > > > > > 
> > > > > > > > > I would add that but the DDC signals are not connected on the
> > > > > > > > > boards I have access to :-/
> > > > > > > > > 
> > > > > > > > >> I'd just kill this and use the connector force support (and
> > > > > > > > >> manually adding the right resolutions).
> > > > > > > > > 
> > > > > > > > > Looks like that's a candidate for better documentation... How
> > > > > > > > > does force support work ?
> > > > > > > > 
> > > > > > > > Grep for DRM_FORCE_ON, iirc it can be set on the commandline,
> > > > > > > > where you can also force a specific mode. The best I could find
> > > > > > > > wrt docs is the kerneldoc for
> > > > > > > > drm_mode_parse_command_line_for_connector. With a bit more
> > > > > > > > reading it looks like it's intermingled with the fbdev helper
> > > > > > > > code, but should be fairly easy to extract and used by your
> > > > > > > > driver.
> > > > > > > 
> > > > > > > It makes sense to force the connector state from command line, but
> > > > > > > I'm not sure if the same mechanism is the best solution here. As
> > > > > > > the driver has no way to know the connector state, the best we can
> > > > > > > do is guess what modes are supported. I can just return 0 in the
> > > > > > > get_modes handler, but then the core will not call
> > > > > > > drm_add_modes_noedid(), and modes will need to be added manually.
> > > > > > > 
> > > > > > > Is your point that for a board on which the VGA connector state
> > > > > > > can't be detected, the user should always be responsible for
> > > > > > > adding all the modes supported by the VGA monitor on the command
> > > > > > > line ?
> > > > > > 
> > > > > > My point is that we already have both an established code for
> > > > > > connected outputs without EDID to add fallback modes and means to
> > > > > > force connectors to certain states. Your code here seems to reinvent
> > > > > > that wheel, so I wonder what we should/need to improve in the common
> > > > > > code to suit your needs.
> > > > > 
> > > > > The currently available code might suit my needs, it might just be
> > > > > that I fail to see how to use it properly.
> > > > > 
> > > > > Regarding the "code for connected outputs without EDID to add fallback
> > > > > modes" you're referring to, is that
> > > > > 
> > > > >         if (count == 0 && connector->status ==
> > > > >         connector_status_connected)
> > > > >                 count = drm_add_modes_noedid(connector, 1024, 768);
> > > > > 
> > > > > in drm_helper_probe_single_connector_modes() ? That function will only
> > > > > be called if the connector status is connector_status_connected. There
> > > > > are two ways to enforce that:
> > > > > 
> > > > > - returning connector_status_connected from the connector detect()
> > > > > operation, which seems to defeat the purpose of having
> > > > > connector_status_unknown completely.
> > > > 
> > > > We might want to add such a default mode also for unknown, I'm not sure.
> > > > Userspace policy is to first try to light up any connected outputs, and
> > > > if> there's none try to light up any unknown outputs. Not sure whether
> > > > userspace (i.e. X) will automatically add a default mode. fbcon might
> > > > also handle this less gracefully.
> > > > 
> > > > Personally I'm ok with extending this to unknown, it shouldn't really
> > > > hurt (since we already try really hard not to leak unknown anywhere
> > > > visible).
> > > 
> > > Do you mean something like
> > > 
> > > diff --git a/drivers/gpu/drm/drm_crtc_helper.c
> > > b/drivers/gpu/drm/drm_crtc_helper.c index f554516..9aae384 100644
> > > --- a/drivers/gpu/drm/drm_crtc_helper.c
> > > +++ b/drivers/gpu/drm/drm_crtc_helper.c
> > > @@ -160,7 +160,8 @@ int drm_helper_probe_single_connector_modes(struct
> > > drm_connector *connector,> 
> > >  #endif
> > >  		count = (*connector_funcs->get_modes)(connector);
> > > -	if (count == 0 && connector->status == connector_status_connected)
> > > +	if (count == 0 && (connector->status == connector_status_connected ||
> > > +			   connector->status == connector_status_unknown))
> > >  		count = drm_add_modes_noedid(connector, 1024, 768);
> > >  	if (count == 0)
> > >  		goto prune;
> > > 
> > > If so I can submit a proper patch.
> > 
> > Yeah, but Ajax is the guy with the opinion that matters here. Cc'ed.
> 
> -- 
> Regards,
> 
> Laurent Pinchart
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch