linux-kernel - Re: [PATCH v2 1/2] drm: Add NVIDIA Tegra20 support

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Date:	Tue, 13 Nov 2012 11:05:27 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Mark Zhang <markz@...dia.com>
Cc:	Dave Airlie <airlied@...hat.com>, Rob Clark <robdclark@...il.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] drm: Add NVIDIA Tegra20 support

On Tue, Nov 13, 2012 at 08:48:22AM +0100, Thierry Reding wrote:
> On Tue, Nov 13, 2012 at 03:15:47PM +0800, Mark Zhang wrote:
> > On 11/13/2012 05:55 AM, Thierry Reding wrote:
[...]
> > > +int tegra_output_init(struct drm_device *drm, struct tegra_output *output)
> > > +{
> > > +       int connector, encoder, err;
> > > +       enum of_gpio_flags flags;
> > > +       struct device_node *ddc;
> > > +       size_t size;
> > > +
> > > +       if (!output->of_node)
> > > +               output->of_node = output->dev->of_node;
> > > +
> > > +       output->edid = of_get_property(output->of_node, "nvidia,edid", &size);
> > > +
> > > +       ddc = of_parse_phandle(output->of_node, "nvidia,ddc-i2c-bus", 0);
> > > +       if (ddc) {
> > > +               output->ddc = of_find_i2c_adapter_by_node(ddc);
> > 
> > The i2c adapter may not be ready at this time. For Tegra 2, the I2C bus
> > for HDMI is not dedicated and we need the i2cmux driver loaded before
> > this i2c can be used. It proved that sometimes i2cmux driver loads after
> > drm driver.
> > 
> > So we need to add some logics to support driver probe deferral here.
> > Anyway, I'm just want you know about this and we can improve this later.
> 
> Good point. Unfortunately tegra_output_init() isn't always used from
> within .probe(), so it isn't quite easy to handle deferred probe here.
> I'll have to take a look at how to solve this properly.

After a closer look at this I think what should be done here is split up
tegra_output_init() into a tegra_output_parse() that does the DT parsing
and tegra_output_init() that actually initializes the output.

I'll try to implement something like that for the next version.

Thierry

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