linux-kernel - Re: [linux-sunxi] [PATCH 3/6] drm/sun4i: dsi: Add bridge support

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Message-ID: <3206b448f031ce22acc2db979781f19c1dded20c.camel@bootlin.com>
Date:   Fri, 15 Mar 2019 14:48:07 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     jagan@...rulasolutions.com, Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Chen-Yu Tsai <wens@...e.org>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...glegroups.com, linux-amarula@...rulasolutions.com
Subject: Re: [linux-sunxi] [PATCH 3/6] drm/sun4i: dsi: Add bridge support

Hi,

On Fri, 2019-03-15 at 14:45 +0100, Maxime Ripard wrote:
> On Fri, Mar 15, 2019 at 02:32:55PM +0100, Paul Kocialkowski wrote:
> > Hi,
> > 
> > On Fri, 2019-03-15 at 18:38 +0530, Jagan Teki wrote:
> > > Some display panels would come up with a non-DSI output which
> > > can have an option to connect DSI interface by means of bridge
> > > convertor.
> > > 
> > > This DSI to non-DSI bridge convertor would require a bridge
> > > driver that would communicate the DSI controller for bridge
> > > functionalities.
> > > 
> > > So, add support for bridge functionalities in Allwinner DSI
> > > controller.
> > 
> > See a few comments below.
> > 
> > > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > > ---
> > >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 65 +++++++++++++++++++-------
> > >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h |  1 +
> > >  2 files changed, 49 insertions(+), 17 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > index 0960b96b62cc..64d74313b842 100644
> > > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > @@ -781,6 +781,9 @@ static void sun6i_dsi_encoder_enable(struct drm_encoder *encoder)
> > >  	if (!IS_ERR(dsi->panel))
> > >  		drm_panel_prepare(dsi->panel);
> > >  
> > > +	if (!IS_ERR(dsi->bridge))
> > > +		drm_bridge_pre_enable(dsi->bridge);
> > > +
> > >  	/*
> > >  	 * FIXME: This should be moved after the switch to HS mode.
> > >  	 *
> > > @@ -796,6 +799,9 @@ static void sun6i_dsi_encoder_enable(struct drm_encoder *encoder)
> > >  	if (!IS_ERR(dsi->panel))
> > >  		drm_panel_enable(dsi->panel);
> > >  
> > > +	if (!IS_ERR(dsi->bridge))
> > > +		drm_bridge_enable(dsi->bridge);
> > > +
> > >  	sun6i_dsi_start(dsi, DSI_START_HSC);
> > >  
> > >  	udelay(1000);
> > > @@ -812,6 +818,9 @@ static void sun6i_dsi_encoder_disable(struct drm_encoder *encoder)
> > >  	if (!IS_ERR(dsi->panel)) {
> > >  		drm_panel_disable(dsi->panel);
> > >  		drm_panel_unprepare(dsi->panel);
> > > +	} else if (!IS_ERR(dsi->bridge)) {
> > > +		drm_bridge_disable(dsi->bridge);
> > > +		drm_bridge_post_disable(dsi->bridge);
> > >  	}
> > >  
> > >  	phy_power_off(dsi->dphy);
> > > @@ -973,11 +982,16 @@ static int sun6i_dsi_attach(struct mipi_dsi_host *host,
> > >  	struct sun6i_dsi *dsi = host_to_sun6i_dsi(host);
> > >  
> > >  	dsi->device = device;
> > > -	dsi->panel = of_drm_find_panel(device->dev.of_node);
> > > -	if (IS_ERR(dsi->panel))
> > > -		return PTR_ERR(dsi->panel);
> > >  
> > > -	dev_info(host->dev, "Attached device %s\n", device->name);
> > > +	dsi->bridge = of_drm_find_bridge(device->dev.of_node);
> > > +	if (!dsi->bridge) {
> > 
> > You are using IS_ERR to check that the bridge is alive in the changes
> > above, but switch to checking that it's non-NULL at this point.
> > 
> > Are both guaranteed to be interchangeable?
> 
> They aren't. Any ERR_PTR will be !NULL
> 
> > > +		dsi->panel = of_drm_find_panel(device->dev.of_node);
> > > +		if (IS_ERR(dsi->panel))
> > > +			return PTR_ERR(dsi->panel);
> > > +	}
> > 
> > You should probably use drm_of_find_panel_or_bridge instead of
> > duplicating the logic here.
> 
> Or we can even use the drm_panel_bridge_add to simplify things.

Indeed, I was just looking at that and it seems to be specifically
tailored for this use case.

Cheers,

Paul

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com