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From: "Klymenko, Anatoliy" <Anatoliy.Klymenko@amd.com>
To: Maxime Ripard <mripard@kernel.org>
CC: Laurent Pinchart <laurent.pinchart@ideasonboard.com>, Maarten Lankhorst
	<maarten.lankhorst@linux.intel.com>, Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>, "Simek,
 Michal" <michal.simek@amd.com>, Andrzej Hajda <andrzej.hajda@intel.com>, Neil
 Armstrong <neil.armstrong@linaro.org>, Robert Foss <rfoss@kernel.org>, Jonas
 Karlman <jonas@kwiboo.se>, Jernej Skrabec <jernej.skrabec@gmail.com>,
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	<linux-arm-kernel@lists.infradead.org>, "linux-kernel@vger.kernel.org"
	<linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 4/4] drm/atomic-helper: Add select_output_bus_format
 callback
Thread-Topic: [PATCH 4/4] drm/atomic-helper: Add select_output_bus_format
 callback
Thread-Index: AQHaapGE8X8PDnmqPkCPFIu/krDfHg==
Date: Wed, 28 Feb 2024 22:00:19 +0000
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Hi Maxime,

Thanks for the review.

> -----Original Message-----
> From: Maxime Ripard <mripard@kernel.org>
> Sent: Wednesday, February 28, 2024 7:30 AM
> To: Klymenko, Anatoliy <Anatoliy.Klymenko@amd.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>; Maarten Lankhor=
st
> <maarten.lankhorst@linux.intel.com>; Thomas Zimmermann
> <tzimmermann@suse.de>; David Airlie <airlied@gmail.com>; Daniel Vetter
> <daniel@ffwll.ch>; Simek, Michal <michal.simek@amd.com>; Andrzej Hajda
> <andrzej.hajda@intel.com>; Neil Armstrong <neil.armstrong@linaro.org>; Ro=
bert
> Foss <rfoss@kernel.org>; Jonas Karlman <jonas@kwiboo.se>; Jernej Skrabec
> <jernej.skrabec@gmail.com>; dri-devel@lists.freedesktop.org; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH 4/4] drm/atomic-helper: Add select_output_bus_format
> callback
>=20
> Hi,
>=20
> On Mon, Feb 26, 2024 at 08:44:45PM -0800, Anatoliy Klymenko wrote:
> > Add select_output_bus_format to CRTC atomic helpers callbacks. This
> > callback Will allow CRTC to participate in media bus format
> > negotiation over connected DRM bridge chain and impose CRTC-specific
> restrictions.
> > A good example is CRTC implemented as FPGA soft IP. This kind of CRTC
> > will most certainly support a single output media bus format, as
> > supporting multiple runtime options consumes extra FPGA resources. A
> > variety of options for FPGA are usually achieved by synthesizing IP
> > with different parameters.
> >
> > Incorporate select_output_bus_format callback into the format
> > negotiation stage to fix the input bus format of the first DRM bridge i=
n the
> chain.
> >
> > Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@amd.com>
> > ---
> >  drivers/gpu/drm/drm_bridge.c             | 19 +++++++++++++++++--
> >  include/drm/drm_modeset_helper_vtables.h | 31
> > +++++++++++++++++++++++++++++++
> >  2 files changed, 48 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_bridge.c
> > b/drivers/gpu/drm/drm_bridge.c index 521a71c61b16..453ae3d174b4 100644
> > --- a/drivers/gpu/drm/drm_bridge.c
> > +++ b/drivers/gpu/drm/drm_bridge.c
> > @@ -32,6 +32,7 @@
> >  #include <drm/drm_edid.h>
> >  #include <drm/drm_encoder.h>
> >  #include <drm/drm_file.h>
> > +#include <drm/drm_modeset_helper_vtables.h>
> >  #include <drm/drm_of.h>
> >  #include <drm/drm_print.h>
> >
> > @@ -879,7 +880,8 @@ static int select_bus_fmt_recursive(struct drm_brid=
ge
> *first_bridge,
> >  	unsigned int i, num_in_bus_fmts =3D 0;
> >  	struct drm_bridge_state *cur_state;
> >  	struct drm_bridge *prev_bridge;
> > -	u32 *in_bus_fmts;
> > +	struct drm_crtc *crtc =3D crtc_state->crtc;
> > +	u32 *in_bus_fmts, in_fmt;
> >  	int ret;
> >
> >  	prev_bridge =3D drm_bridge_get_prev_bridge(cur_bridge);
> > @@ -933,7 +935,20 @@ static int select_bus_fmt_recursive(struct drm_bri=
dge
> *first_bridge,
> >  		return -ENOMEM;
> >
> >  	if (first_bridge =3D=3D cur_bridge) {
> > -		cur_state->input_bus_cfg.format =3D in_bus_fmts[0];
> > +		in_fmt =3D in_bus_fmts[0];
> > +		if (crtc->helper_private &&
> > +		    crtc->helper_private->select_output_bus_format) {
> > +			in_fmt =3D crtc->helper_private-
> >select_output_bus_format(
> > +							crtc,
> > +							crtc->state,
> > +							in_bus_fmts,
> > +							num_in_bus_fmts);
> > +			if (!in_fmt) {
> > +				kfree(in_bus_fmts);
> > +				return -ENOTSUPP;
> > +			}
> > +		}
> > +		cur_state->input_bus_cfg.format =3D in_fmt;
>=20
> I don't think we should start poking at the CRTC internals, but we should=
 rather
> provide a helper here.

Makes sense, thank you. ACK.

>=20
> >  		cur_state->output_bus_cfg.format =3D out_bus_fmt;
> >  		kfree(in_bus_fmts);
> >  		return 0;
> > diff --git a/include/drm/drm_modeset_helper_vtables.h
> > b/include/drm/drm_modeset_helper_vtables.h
> > index 881b03e4dc28..7c21ae1fe3ad 100644
> > --- a/include/drm/drm_modeset_helper_vtables.h
> > +++ b/include/drm/drm_modeset_helper_vtables.h
> > @@ -489,6 +489,37 @@ struct drm_crtc_helper_funcs {
> >  				     bool in_vblank_irq, int *vpos, int *hpos,
> >  				     ktime_t *stime, ktime_t *etime,
> >  				     const struct drm_display_mode *mode);
> > +
> > +	/**
> > +	 * @select_output_bus_format
> > +	 *
> > +	 * Called by the first connected DRM bridge to negotiate input media
> > +	 * bus format. CRTC is expected to pick preferable media formats from
> > +	 * the list supported by the DRM bridge chain.
>=20
> There's nothing restricting it to bridges here. Please rephrase this to r=
emove the
> bridge mention. The user is typically going to be the encoder, and bridge=
s are just
> an automagic implementation of an encoder.
>=20

OK. I'll fix than in the next version.

> And generally speaking, I'd really like to have an implementation availab=
le before
> merging this.
>

Well, 2 instances of this callback implementations exist as drafts, as this=
 is the new API. A little bit of a chicken and egg problem. I'll try to gro=
om at least one of them into upstreamable shape and attach it to the patch =
set.

> Maxime

-Anatoliy