linux-kernel - Re: [PATCH v4 02/11] drm/bridge: dw-hdmi: add max bpc connector property

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Message-ID: <20200302091818.GC11960@pendragon.ideasonboard.com>
Date:   Mon, 2 Mar 2020 11:18:18 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Jernej Škrabec <jernej.skrabec@...l.net>,
        a.hajda@...sung.com, jonas@...boo.se,
        boris.brezillon@...labora.com, linux-amlogic@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v4 02/11] drm/bridge: dw-hdmi: add max bpc connector
 property

Hi Neil and Jonas,

(CC'ing Daniel for a framework question)

Thank you for the patch.

On Fri, Feb 21, 2020 at 09:50:18AM +0100, Neil Armstrong wrote:
> On 17/02/2020 07:38, Jernej Škrabec wrote:
> > Dne četrtek, 06. februar 2020 ob 20:18:25 CET je Neil Armstrong napisal(a):
> >> From: Jonas Karlman <jonas@...boo.se>
> >>
> >> Add the max_bpc property to the dw-hdmi connector to prepare support
> >> for 10, 12 & 16bit output support.
> >>
> >> Signed-off-by: Jonas Karlman <jonas@...boo.se>
> >> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
> >> ---
> >>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c index
> >> 9e0927d22db6..051001f77dd4 100644
> >> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> @@ -2406,6 +2406,10 @@ static int dw_hdmi_bridge_attach(struct drm_bridge
> >> *bridge) DRM_MODE_CONNECTOR_HDMIA,
> >>  				    hdmi->ddc);
> >>
> >> +	drm_atomic_helper_connector_reset(connector);
> > 
> > Why is this reset needed?
> 
> I assume it's to allocate a new connector state to attach a the bpc propery.
> 
> But indeed, this helper is never used here, but only as callback to the drm_connector_funcs->reset.
> 
> But, amdgpu calls :
> 	/*
> 	 * Some of the properties below require access to state, like bpc.
> 	 * Allocate some default initial connector state with our reset helper.
> 	 */
> 	if (aconnector->base.funcs->reset)
> 		aconnector->base.funcs->reset(&aconnector->base);
> 
> which is the same.

A comment would be useful:

	/*
	 * drm_connector_attach_max_bpc_property() requires the
	 * connector to have a state.
	 */
	drm_atomic_helper_connector_reset(connector);

	drm_connector_attach_max_bpc_property(connector, 8, 16);

I don't like this much though, it feels like the initial reset performed
by drm_mode_config_reset() should set default values for all state
members that are related to properties. Daniel, what's the rationale
behind the current implementation ?

This is a DRM core issue that shouldn't block this patch though, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> >> +
> >> +	drm_connector_attach_max_bpc_property(connector, 8, 16);
> >> +
> >>  	if (hdmi->version >= 0x200a && hdmi->plat_data->use_drm_infoframe)
> >>  		drm_object_attach_property(&connector->base,
> >>  			connector->dev-
> >> mode_config.hdr_output_metadata_property, 0);

-- 
Regards,

Laurent Pinchart