Re: [PATCH v5 09/20] drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers

From: Doug Anderson <dianders@chromium.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Andrzej Hajda <a.hajda@samsung.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Jernej Skrabec <jernej.skrabec@siol.net>,
	Sam Ravnborg <sam@ravnborg.org>, Wolfram Sang <wsa@kernel.org>,
	MSM <linux-arm-msm@vger.kernel.org>,
	Rob Clark <robdclark@chromium.org>,
	Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>,
	Stephen Boyd <swboyd@chromium.org>,
	Steev Klimaszewski <steev@kali.org>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	linux-i2c <linux-i2c@vger.kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	"open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
	Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
	Robert Foss <robert.foss@linaro.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 09/20] drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers
Date: Mon, 3 May 2021 09:55:20 -0700	[thread overview]
Message-ID: <CAD=FV=XGYHNasnqaFopUnuZNaBn+Nbf4+ak7vUoERaA8pRBTsw@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdbZxauBFLvR_MMx4WD+K6DftK19Fivt_mkE=+Xr2EPUvQ@mail.gmail.com>

Hi,

On Sat, May 1, 2021 at 4:59 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Fri, Apr 23, 2021 at 6:59 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> > Let's use the newly minted aux bus to break up the driver into sub
> > drivers. We're not doing a full breakup here: all the code is still in
> > the same file and remains largely untouched. The big goal here of
> > using sub-drivers is to allow part of our code to finish probing even
> > if some other code needs to defer. This can solve some chicken-and-egg
> > problems. Specifically:
> > - In commit 48834e6084f1 ("drm/panel-simple: Support hpd-gpios for
> >   delaying prepare()") we had to add a bit of a hack to simpel-panel
> >   to support HPD showing up late. We can get rid of that hack now
> >   since the GPIO part of our driver can finish probing early.
> > - We have a desire to expose our DDC bus to simple-panel (and perhaps
> >   to a backlight driver?). That will end up with the same
> >   chicken-and-egg problem. A future patch to move this to a sub-driver
> >   will fix it.
> > - If/when we support the PWM functionality present in the bridge chip
> >   for a backlight we'll end up with another chicken-and-egg
> >   problem. If we allow the PWM to be a sub-driver too then it solves
> >   this problem.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> > Changes in v5:
> > - Fix module compile problems (Bjorn + kbuild bot)
> > - Remove useless MODULE_DEVICE_TABLE (Bjorn).
>
> This is generally a good idea. I have no idea when to use
> auxbus or MFD

It was a bit hard for me to figure out too. I think historically this
could have been implemented by MFD but I believe that the point of
introducing the AUX bus was that MFD wasn't a great fit for things
like this. It's talked about a bit in
"Documentation/driver-api/auxiliary_bus.rst". For me the important
thing here is that we think of the bridge chip as one device, not a
collection of IP blocks glued together in one package. As some
evidence, the DT bindings don't have sub-nodes for this. There's a
single DT node that says that this one device is the bridge, is a GPIO
controller, and can provide a PWM.

> but I trust that you researched that so:
> Acked-by: Linus Walleij <linus.walleij@linaro.org>

Thanks! I'll land it then to whittle the patch stack down to just the
controversial EDID one.

-Doug