[PATCH v4 1/4] drm: Introduce generic probe function for component based masters.

[Liviu Dudau]

On Tue, Oct 20, 2015 at 11:09:09AM +0100, Russell King - ARM Linux wrote:
> On Tue, Oct 20, 2015 at 11:00:55AM +0100, Emil Velikov wrote:
> > Hi Liviu,
> > 
> > On 20 October 2015 at 10:23, Liviu Dudau <Liviu.Dudau at arm.com> wrote:
> > > A lot of component based DRM drivers use a variant of the same code
> > > as the probe function. They bind the crtc ports in the first iteration
> > > and then scan through the child nodes and bind the encoders attached
> > > to the remote endpoints. Factor the common code into a separate
> > > function called drm_of_component_probe() in order to increase code
> > > reuse.
> > >
> > > Cc: David Airlie <airlied at linux.ie>
> > > Signed-off-by: Liviu Dudau <Liviu.Dudau at arm.com>
> > > Acked-by: Russell King <rmk+kernel at arm.linux.org.uk>
> > > ---
> > >  drivers/gpu/drm/drm_of.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++
> > >  include/drm/drm_of.h     | 13 +++++++
> > >  2 files changed, 101 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> > > index be38840..493c05c 100644
> > > --- a/drivers/gpu/drm/drm_of.c
> > > +++ b/drivers/gpu/drm/drm_of.c
> > > @@ -1,3 +1,4 @@
> > > +#include <linux/component.h>
> > >  #include <linux/export.h>
> > >  #include <linux/list.h>
> > >  #include <linux/of_graph.h>
> > > @@ -61,3 +62,90 @@ uint32_t drm_of_find_possible_crtcs(struct drm_device *dev,
> > >         return possible_crtcs;
> > >  }
> > >  EXPORT_SYMBOL(drm_of_find_possible_crtcs);
> > > +
> > > +/**
> > > + * drm_of_component_probe - Generic probe function for a component based master
> > > + * @dev: master device containing the OF node
> > > + * @compare_of: compare function used for matching components
> > > + * @master_ops: component master ops to be used
> > > + *
> > > + * Parse the platform device OF node and bind all the components associated
> > > + * with the master. Interface ports are added before the encoders in order to
> > > + * satisfy their .bind requirements
> > > + * See Documentation/devicetree/bindings/graph.txt for the bindings.
> > > + *
> > > + * Returns zero if successful, or one of the standard error codes if it fails.
> > > + */
> > > +int drm_of_component_probe(struct device *dev,
> > > +                          int (*compare_of)(struct device *, void *),
> > > +                          const struct component_master_ops *m_ops)
> > > +{
> > > +       struct device_node *ep, *port, *remote;
> > > +       struct component_match *match = NULL;
> > > +       int i;
> > > +
> > > +       if (!dev->of_node)
> > > +               return -EINVAL;
> > > +
> > > +       /*
> > > +        * Bind the crtc's ports first, so that drm_of_find_possible_crtcs()
> > > +        * called from encoder's .bind callbacks works as expected
> > > +        */
> > > +       for (i = 0; ; i++) {
> > > +               port = of_parse_phandle(dev->of_node, "ports", i);
> > > +               if (!port)
> > > +                       break;
> > > +
> > > +               if (!of_device_is_available(port->parent)) {
> > > +                       of_node_put(port);
> > > +                       continue;
> > > +               }
> > > +
> > > +               component_match_add(dev, &match, compare_of, port);
> > > +               of_node_put(port);
> > > +       }
> > > +
> > > +       if (i == 0) {
> > > +               dev_err(dev, "missing 'ports' property\n");
> > > +               return -ENODEV;
> > > +       }
> > > +
> > > +       if (!match) {
> > > +               dev_err(dev, "no available port\n");
> > > +               return -ENODEV;
> > > +       }
> > > +
> > > +       /*
> > > +        * For bound crtcs, bind the encoders attached to their remote endpoint
> > > +        */
> > > +       for (i = 0; ; i++) {
> > > +               port = of_parse_phandle(dev->of_node, "ports", i);
> > > +               if (!port)
> > > +                       break;
> > > +
> > > +               if (!of_device_is_available(port->parent)) {
> > > +                       of_node_put(port);
> > > +                       continue;
> > > +               }
> > > +
> > Of the three drivers converted only the rockchip one has the above
> > of_device_is_available() hunk. Based on the handling in previous loop
> > I'm not entirely sure if it's needed, but if so shouldn't one mention
> > the difference when converting the respective drivers ?
> 
> Yes, it should've been there, otherwise we'll end up binding encoders
> which are connected to a CRTC which has been disabled - and that means
> the DRM driver won't come up.

That's my understanding as well. As mentioned in the cover letter, the generic
function tries to gather together the best practice and be more complete than
the individual versions found in the drivers. So you get additional checks
that should've been in there in the first place if it were not for the code
being spread out.

Best regards,
Liviu

> 
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