Re: [PATCH v2 2/2] drm/bridge: Add PTN3460 bridge driver

[Thierry Reding <thierry.reding@gmail.com>]

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On Thu, Aug 15, 2013 at 03:32:58PM -0400, Sean Paul wrote:
> On Thu, Aug 15, 2013 at 11:28 AM, Thierry Reding
> <thierry.reding@gmail.com> wrote:
> > On Wed, Aug 14, 2013 at 04:47:38PM -0400, Sean Paul wrote:
> > [...]
> >> +int ptn3460_init(struct drm_device *dev, struct drm_encoder *encoder,
> >> +             struct i2c_client *client, struct device_node *node)
> > [...]
> >> +     ptn_bridge->gpio_pd_n = of_get_named_gpio(node, "powerdown-gpio", 0);
> >
> > of_get_named_gpio() can return -EPROBE_DEFER and I wonder how you handle
> > that in the driver that uses ptn3460_init(). Since you pass in an
> > initialized drm_device, you'd need to undo all of that in case of
> > -EPROBE_DEFER. Well I guess you'd have to do that in case of any error,
> > but it makes things difficult to handle for drivers.
> >
> > For instance on Tegra we pretty much delay DRM initialization until all
> > required subdevices (there are quite a few) have been probed, so if we
> > wanted to use this function we'd have to call it after all drivers have
> > been probed because only then do we have access to a struct drm_device.
> > That will cause other problems, however, because at that point we can't
> > defer probing anymore.
> >
> 
> I suppose I could add another init that performs the deferrable tasks
> (ptn3460_init_deferrable or something). This would be called before
> drm init has been started from one of the probe functions.
> Alternatively, I could set this up as a standalone i2c driver and do
> this stuff in the probe. Any other options?

My point was that in those cases you don't have access to the DRM device
yet since you haven't called drm_init() yet.

> Adding another init call adds yet another thing the drm driver has to
> do to use this bridge. Making the ptn driver standalone requires you
> to set things up such that drm init is dependent on ptn probe running
> successfully. I'm not sure which is more desirable.
> 
> Practically speaking, do you expect to call drm_init before the gpio
> is available?

No, not really, but I won't know that the GPIO is available until I
actually call of_get_named_gpio_flags().

But perhaps we should cross that bridge when we get to it.

Thierry

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