netdev - Re: [PATCH v5 5/6] drm: sun4i: Add support for enabling DDC I2C bus to sun8i_dw

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Date:   Thu, 23 May 2019 14:27:01 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     linux-sunxi@...glegroups.com, Chen-Yu Tsai <wens@...e.org>,
        Rob Herring <robh+dt@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v5 5/6] drm: sun4i: Add support for enabling DDC I2C bus
 to sun8i_dw_hdmi glue

On Tue, May 21, 2019 at 02:15:19PM +0200, Ondřej Jirman wrote:
> Hi Maxime,
>
> On Tue, May 21, 2019 at 01:46:11PM +0200, Maxime Ripard wrote:
> > Hi,
> >
> > On Tue, May 21, 2019 at 01:50:08AM +0200, megous@...ous.com wrote:
> > > From: Ondrej Jirman <megous@...ous.com>
> > >
> > > Orange Pi 3 board requires enabling a voltage shifting circuit via GPIO
> > > for the DDC bus to be usable.
> > >
> > > Add support for hdmi-connector node's optional ddc-en-gpios property to
> > > support this use case.
> > >
> > > Signed-off-by: Ondrej Jirman <megous@...ous.com>
> > > ---
> > >  drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c | 55 +++++++++++++++++++++++++--
> > >  drivers/gpu/drm/sun4i/sun8i_dw_hdmi.h |  3 ++
> > >  2 files changed, 55 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c b/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c
> > > index 39d8509d96a0..59b81ba02d96 100644
> > > --- a/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c
> > > +++ b/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c
> > > @@ -98,6 +98,30 @@ static u32 sun8i_dw_hdmi_find_possible_crtcs(struct drm_device *drm,
> > >  	return crtcs;
> > >  }
> > >
> > > +static int sun8i_dw_hdmi_find_connector_pdev(struct device *dev,
> > > +					     struct platform_device **pdev_out)
> > > +{
> > > +	struct platform_device *pdev;
> > > +	struct device_node *remote;
> > > +
> > > +	remote = of_graph_get_remote_node(dev->of_node, 1, -1);
> > > +	if (!remote)
> > > +		return -ENODEV;
> > > +
> > > +	if (!of_device_is_compatible(remote, "hdmi-connector")) {
> > > +		of_node_put(remote);
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	pdev = of_find_device_by_node(remote);
> > > +	of_node_put(remote);
> > > +	if (!pdev)
> > > +		return -ENODEV;
> > > +
> > > +	*pdev_out = pdev;
> > > +	return 0;
> > > +}
> > > +
> > >  static int sun8i_dw_hdmi_bind(struct device *dev, struct device *master,
> > >  			      void *data)
> > >  {
> > > @@ -151,16 +175,29 @@ static int sun8i_dw_hdmi_bind(struct device *dev, struct device *master,
> > >  		return PTR_ERR(hdmi->regulator);
> > >  	}
> > >
> > > +	ret = sun8i_dw_hdmi_find_connector_pdev(dev, &hdmi->connector_pdev);
> > > +	if (!ret) {
> > > +		hdmi->ddc_en = gpiod_get_optional(&hdmi->connector_pdev->dev,
> > > +						  "ddc-en", GPIOD_OUT_HIGH);
> > > +		if (IS_ERR(hdmi->ddc_en)) {
> > > +			platform_device_put(hdmi->connector_pdev);
> > > +			dev_err(dev, "Couldn't get ddc-en gpio\n");
> > > +			return PTR_ERR(hdmi->ddc_en);
> > > +		}
> > > +	}
> > > +
> > >  	ret = regulator_enable(hdmi->regulator);
> > >  	if (ret) {
> > >  		dev_err(dev, "Failed to enable regulator\n");
> > > -		return ret;
> > > +		goto err_unref_ddc_en;
> > >  	}
> > >
> > > +	gpiod_set_value(hdmi->ddc_en, 1);
> > > +
> >
> > Do you really need this to be done all the time? I'm guessing you
> > would only need this when running .get_modes, right?
>
> I don't think it hurts anything. Enabled voltage shifting circuit doesn't
> draw any current, unless DDC is actually transmitting data. On most boards
> I'd imagine this circuit is always on anyway (Orange Pi 3 schematic even has
> an option to tie this signal to VCC-IO instead of GPIO).

Ok, it works for me then

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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