[RFC V2 1/3] drm: implement chaining of drm bridges

[Ajay kumar]

Sean,


On Tue, May 6, 2014 at 9:25 PM, Sean Paul <seanpaul at chromium.org> wrote:
> On Mon, May 5, 2014 at 12:52 PM, Ajay Kumar <ajaykumar.rs at samsung.com> wrote:
>> As of now, we can have only one bridge hanging off the encoder.
>> With this patch, we allow multiple bridges to hang onto the same encoder
>> with the use of a simple next_bridge ptr.
>>
>> The drm core calls bridge->funcs for the first bridge which
>> is attached to it, and its upto the individual bridge drivers
>> to call bridge->funcs for the next bridge in the chain.
>>
>> Signed-off-by: Ajay Kumar <ajaykumar.rs at samsung.com>
>> ---
>>  drivers/gpu/drm/drm_crtc.c | 13 ++++++++++++-
>>  include/drm/drm_crtc.h     |  2 ++
>>  2 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
>> index d8b7099..fe9905f 100644
>> --- a/drivers/gpu/drm/drm_crtc.c
>> +++ b/drivers/gpu/drm/drm_crtc.c
>> @@ -918,8 +918,10 @@ EXPORT_SYMBOL(drm_connector_unplug_all);
>>   * Zero on success, error code on failure.
>>   */
>>  int drm_bridge_init(struct drm_device *dev, struct drm_bridge *bridge,
>> -               const struct drm_bridge_funcs *funcs)
>> +                       struct drm_encoder *encoder,
>> +                       const struct drm_bridge_funcs *funcs)
>
>
> IMO, we should let whoever is spawning the bridges chain them
> together, instead of passing encoder in init().
For this, we have to modify drm_bridge_init to return a bridge pointer and
then, as Rob is suggesting, we can have some helper functions to update
next_bridge ptr to form a bridge chain, and these functions can be called from
the corresponding encoder implementation.

Ajay

>>  {
>> +       struct drm_bridge *temp;
>>         int ret;
>>
>>         drm_modeset_lock_all(dev);
>> @@ -931,6 +933,15 @@ int drm_bridge_init(struct drm_device *dev, struct drm_bridge *bridge,
>>         bridge->dev = dev;
>>         bridge->funcs = funcs;
>>
>> +       if (encoder->bridge) {
>> +               temp = encoder->bridge;
>> +               while (temp->next_bridge)
>> +                       temp = temp->next_bridge;
>> +
>> +               temp->next_bridge = bridge;
>> +       } else
>> +               encoder->bridge = bridge;
>> +
>>         list_add_tail(&bridge->head, &dev->mode_config.bridge_list);
>>         dev->mode_config.num_bridge++;
>>
>> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
>> index e55fccb..bb6ed88 100644
>> --- a/include/drm/drm_crtc.h
>> +++ b/include/drm/drm_crtc.h
>> @@ -619,6 +619,7 @@ struct drm_bridge_funcs {
>>  struct drm_bridge {
>>         struct drm_device *dev;
>>         struct list_head head;
>> +       struct drm_bridge *next_bridge;
>>
>>         struct drm_mode_object base;
>>
>> @@ -862,6 +863,7 @@ extern void drm_connector_cleanup(struct drm_connector *connector);
>>  extern void drm_connector_unplug_all(struct drm_device *dev);
>>
>>  extern int drm_bridge_init(struct drm_device *dev, struct drm_bridge *bridge,
>> +                          struct drm_encoder *encoder,
>>                            const struct drm_bridge_funcs *funcs);
>>  extern void drm_bridge_cleanup(struct drm_bridge *bridge);
>>
>> --
>> 1.8.1.2
>>