[PATCH v2 2/3] drm/edid: Implement SCDC support detection

[Daniel Vetter]

On Mon, Dec 05, 2016 at 06:11:44PM +0100, Thierry Reding wrote:
> On Mon, Dec 05, 2016 at 05:21:24PM +0100, Daniel Vetter wrote:
> > On Mon, Dec 05, 2016 at 12:11:46PM +0100, Thierry Reding wrote:
> > > On Mon, Dec 05, 2016 at 09:16:27AM +0100, Daniel Vetter wrote:
> > > > On Mon, Dec 05, 2016 at 08:57:43AM +0100, Thierry Reding wrote:
> > > > > On Sat, Dec 03, 2016 at 04:35:24AM +0000, Sharma, Shashank wrote:
> > > > > > Hi Thierry, 
> > > > > > 
> > > > > > If you can please have a look on this patch, I had written one to parse HF-VSDB, which was covering SCDC detection too. 
> > > > > > https://patchwork.kernel.org/patch/9452259/ 
> > > > > 
> > > > > I think there had been pushback before about caching capabilities from
> > > > > EDID, so from that point of view my patch is more inline with existing
> > > > > EDID parsing API.
> > > > 
> > > > Hm, where was that pushback? We do have a bit a mess between explicitly
> > > > parsing stuff (e.g. eld) and stuffing parsed data into drm_display_info.
> > > 
> > > You did object to a very similar patch some time ago that did a similar
> > > thing for DPCD stuff. And also Villa had commented on an earlier patch
> > > from Jose about concerns of bloating core structures:
> > > 
> > > 	https://patchwork.freedesktop.org/patch/104806/
> > 
> > DPCD I complained about because somehow we ended up with 2 sets of
> > helpers, one filling a struct and the others returning directly. I
> > objected to the fact that there's 2 (and imo your patch duplicated even
> > more), not that I think one approach is clearly inferior to the other.
> 
> My recollection is that I had proposed that I do the work of
> transitioning users of the parsers to the cached information but you had
> said that it wasn't worth the churn and that we should just go with the
> existing scheme of passing around the DPCD buffer and extending the
> parsers as necessary.

Hm, I guess it wasn't clear to me that you've offered to do all the
conversions. Doing that would be awesome I think (but quite a bit of
work), and if we bother with it, parsing into a struct is imo the better
idea long-term.

> From that I inferred that the same would be true for EDID and since we
> already have a couple of helpers that operate on struct edid * and which
> return features, continuing that scheme was preferred.
> 
> Anyway, I don't really care either way. Maybe you and Ville can duke it
> out whether or not we want all of the fields parsed, irrespective of
> whether or not they will be used. Then I'll go with whatever you decide.
> 
> > Demanding that there's some real users is also a valid point.
> > 
> > > > I think long-term stuffing it into drm_display_info is probably better,
> > > > since then we only have 1 interaction point between the probe code and the
> > > > atomic_check code. That should be useful for eventually fixing the lack of
> > > > locking between the two, if I ever get around to that ;-)
> > > 
> > > I don't really have objections to caching the results of parsing, it's
> > > what I had proposed and what seemed most natural back when I was working
> > > on the DPCD helpers. But if we now agree that this is the preferred way
> > > to do things, then we should at least agree that it applies to all areas
> > > for the sake of consistency.
> > > 
> > > Also, it might be worth looking into improving the structures, and maybe
> > > adding new ones to order things more conveniently or at least group them
> > > in some logical way. In my opinion some of our data structures are
> > > becoming somewhat... unwieldy.
> > 
> > We're pretty good at consuming fairly invasive refactorings in drm-misc.
> > So it just boils down to get some agreement on what things should look
> > like (+1 from my side to parsing stuff into structs as a general idea),
> > and then massaging all the existing users of the "wrong" interface using
> > cocci and sed.
> > 
> > Unfortunately "just" ;-)
> 
> I think by now it would be useful to have a nested structure within
> struct drm_display_info that contains HDMI specific bits. We already
> have a number of candidates that could be extracted into such a
> structure (drm_detect_hdmi_monitor(), drm_detect_monitor_audio(),
> drm_rgb_quant_range_selectable(), ...).
> 
> Another possibility would be to subclass struct drm_display_info, as
> in:
> 
> 	struct drm_hdmi_info {
> 		struct drm_display_info display;
> 
> 		/* HDMI specific information */
> 		...
> 	};
> 
> Or yet another would be to create struct drm_hdmi_info as a separate
> structure and provide a helper which will extract the necessary info
> from the EDID. Drivers could then store that in driver-private data
> whereas struct drm_display_info could be reduced to the generic bits
> that it used to have.

I think nested drm_hdmi_info within drm_display_info sounds like a fine
idea.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch