linux-kernel - Re: [PATCH v5 2/7] drm/panel: simple: Add ability to override typical timing

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Date:   Wed, 10 Jul 2019 15:56:39 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     devicetree@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Enric Balletbò <enric.balletbo@...labora.com>,
        Stéphane Marchesin <marcheu@...omium.org>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v5 2/7] drm/panel: simple: Add ability to override typical timing

Hi,

On Mon, Jul 8, 2019 at 10:56 AM Sam Ravnborg <sam@...nborg.org> wrote:
>
> On Mon, Jul 01, 2019 at 09:39:06AM -0700, Doug Anderson wrote:
> > Hi,
> >
> > On Sun, Jun 30, 2019 at 1:55 PM Sam Ravnborg <sam@...nborg.org> wrote:
> > >
> > > Hi Douglas.
> > >
> > > > > +
> > > > > +   /* Only add timings if override was not there or failed to validate */
> > > > > +   if (num == 0 && panel->desc->num_timings)
> > > > > +           num = panel_simple_get_timings_modes(panel);
> > > > > +
> > > > > +   /*
> > > > > +    * Only add fixed modes if timings/override added no mode.
> > > >
> > > > This part I fail to understand.
> > > > If we have a panel where we in panel-simple have specified the timings,
> > > > and done so using display_timing so with proper {min, typ, max} then it
> > > > should be perfectly legal to specify a more precise variant in the DT
> > > > file.
> > > > Or what did I miss here?
> > >
> > > Got it now.
> > > If display_mode is used for timings this is what you call "fixed mode".
> > > Hmm, if I got confused someone else may also be confused by this naming.
> >
> > The name "fixed mode" comes from the old code, though I guess in the
> > old code it used to refer to a mode that came from either the
> > display_timing or the display_mode.
> >
> > How about if I call it "panel_simple_get_from_fixed_display_mode"?
> > ...or if you have another suggestion feel free to chime in.
> What we really want to distingush here is the use of display_mode
> and display_timings (if I got the names right).
> That display_mode specify a fixed timing and display_timing specify
> a valid range is something in the semantics of the two types.
> So naming that refer to display_mode versus display_timing will make the
> code simpler to understand. and then a nice comment that when
> display_mode
> is used one looses the possibility to use override_mode.
> That would be fine to have in the struct in the driver.

OK, I can change the names here and try to find a good place to add a comment.


> > NOTE: Since this feedback is minor and this patch has been outstanding
> > for a while (and is blocking other work), I am assuming that the best
> > path forward is for Heiko to land this patch with Thierry's Ack and
> > I'll send a follow-up.  Please yell if you disagree.
> Let's give the patches a spin more as we have passed the possibility for
> the current merge window.

Any way I can convince you to change your mind here?  There are no
functional changes requested so far in your feedback and no bugs--it's
just a few variable names and comments.  By landing the existing
patches as-is:

1. We stop spamming all the people CCed on this whole series (which
includes device tree patches) that might be interested in the series
as a whole but aren't interested in details.

2. We can debate the bikeshed-type issues on their own merit and I
don't have to debate removing existing Acks / Reviewed-by / Tested-by
tags as I make changes.

3. Even if it's not a good time to land the patches right now we know
that these patches will be ready to land as soon as the window opens.
As I mentioned earlier these patches are blocking other work [1] and
landing that patch is actually preventing Matthias from submitting
another series of patches to add support for rk3288-veyron-tiger and
rk3288-veyron-fievel.  Certainly I know that upstream doesn't make a
policy of landing things just to suit the timelines of a downstream
project, but in this case there seems very little downsides to landing
the existing patches and taking a later cleanup patch.


> I am on vacation at the moment and thus slow in responses, but will be back
> at the home office next week and will be more responsive again.
>
>         Sam - who is enjoying the alps in Austria

Hope you have had a great vacation!

[1] https://lkml.kernel.org/r/20190625222629.154619-1-mka@chromium.org

-Doug