Re: [PATCH v2 26/26] drm/bridge: establish a link between the bridge supplier and consumer

[Peter Rosin <peda@axentia.se>]

On 2018-05-15 12:22, Daniel Vetter wrote:
> On Mon, May 14, 2018 at 10:40 PM, Peter Rosin <peda@axentia.se> wrote:
>> On 2018-05-14 18:28, Daniel Vetter wrote:
>>> On Fri, May 11, 2018 at 09:37:47AM +0200, Peter Rosin wrote:
>>>> On 2018-05-10 10:10, Andrzej Hajda wrote:
>>>>> On 04.05.2018 15:52, Peter Rosin wrote:
>>>>>> If the bridge supplier is unbound, this will bring the bridge consumer
>>>>>> down along with the bridge. Thus, there will no longer linger any
>>>>>> dangling pointers from the bridge consumer (the drm_device) to some
>>>>>> non-existent bridge supplier.
>>>>>>
>>>>>> Signed-off-by: Peter Rosin <peda@axentia.se>
>>>>>> ---
>>>>>>  drivers/gpu/drm/drm_bridge.c | 18 ++++++++++++++++++
>>>>>>  include/drm/drm_bridge.h     |  2 ++
>>>>>>  2 files changed, 20 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>>>>>> index 78d186b6831b..0259f0a3ff27 100644
>>>>>> --- a/drivers/gpu/drm/drm_bridge.c
>>>>>> +++ b/drivers/gpu/drm/drm_bridge.c
>>>>>> @@ -26,6 +26,7 @@
>>>>>>  #include <linux/mutex.h>
>>>>>>
>>>>>>  #include <drm/drm_bridge.h>
>>>>>> +#include <drm/drm_device.h>
>>>>>>  #include <drm/drm_encoder.h>
>>>>>>
>>>>>>  #include "drm_crtc_internal.h"
>>>>>> @@ -127,12 +128,25 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>>>>>>    if (bridge->dev)
>>>>>>            return -EBUSY;
>>>>>>
>>>>>> +  if (encoder->dev->dev != bridge->odev) {
>>>>>
>>>>> I wonder why device_link_add does not handle this case (self dependency)
>>>>> silently as noop, as it seems to be a correct behavior.
>>>>
>>>> It's kind-of a silly corner-case though, so perfectly understandable
>>>> that it isn't handled.
>>>>
>>>>>> +          bridge->link = device_link_add(encoder->dev->dev,
>>>>>> +                                         bridge->odev, 0);
>>>>>> +          if (!bridge->link) {
>>>>>> +                  dev_err(bridge->odev, "failed to link bridge to %s\n",
>>>>>> +                          dev_name(encoder->dev->dev));
>>>>>> +                  return -EINVAL;
>>>>>> +          }
>>>>>> +  }
>>>>>> +
>>>>>>    bridge->dev = encoder->dev;
>>>>>>    bridge->encoder = encoder;
>>>>>>
>>>>>>    if (bridge->funcs->attach) {
>>>>>>            ret = bridge->funcs->attach(bridge);
>>>>>>            if (ret < 0) {
>>>>>> +                  if (bridge->link)
>>>>>> +                          device_link_del(bridge->link);
>>>>>> +                  bridge->link = NULL;
>>>>>>                    bridge->dev = NULL;
>>>>>>                    bridge->encoder = NULL;
>>>>>>                    return ret;
>>>>>> @@ -159,6 +173,10 @@ void drm_bridge_detach(struct drm_bridge *bridge)
>>>>>>    if (bridge->funcs->detach)
>>>>>>            bridge->funcs->detach(bridge);
>>>>>>
>>>>>> +  if (bridge->link)
>>>>>> +          device_link_del(bridge->link);
>>>>>> +  bridge->link = NULL;
>>>>>> +
>>>>>>    bridge->dev = NULL;
>>>>>>  }
>>>>>>
>>>>>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
>>>>>> index b656e505d11e..804189c63a4c 100644
>>>>>> --- a/include/drm/drm_bridge.h
>>>>>> +++ b/include/drm/drm_bridge.h
>>>>>> @@ -261,6 +261,7 @@ struct drm_bridge_timings {
>>>>>>   * @list: to keep track of all added bridges
>>>>>>   * @timings: the timing specification for the bridge, if any (may
>>>>>>   * be NULL)
>>>>>> + * @link: drm consumer <-> bridge supplier
>>>>>
>>>>> Nitpick: "<->" suggests symmetry, maybe "device link from drm consumer
>>>>> to the bridge" would be better.
>>>>
>>>> I meant "<->" to indicate that the link is bidirectional, not that the
>>>> relationship is in any way symmetric. I wasn't aware of any implication
>>>> of a symmetric relationship when using "<->", do you have a reference?
>>>> But I guess the different arrow notations in math are somewhat overloaded
>>>> and that someone at some point must have used "<->" to indicate a
>>>> symmetric relationship...
>>>
>>> Yeah I agree with Andrzej here, for me <-> implies a symmetric
>>> relationship. Spelling it out like Andrzej suggested sounds like the
>>> better idea.
>>> -Daniel
>>
>> Ok, I guess that means I have to do a v3 after all. Or can this
>> trivial documentation update be done by the committer? I hate to
>> spam everyone with another volley...
>>
>> Or perhaps I should squash patches 2-23 that are all rather similar
>> and mechanic? I separated them to allow for easier review from
>> individual driver maintainers, but that didn't seem to happen
>> anyway...
> 
> Do another volley of the full set, or in-reply-to to just replace the
> patch that needs to be respun (but some people don't like that).
> 
> When resending just make sure you're picking up all the acks/r-bs you
> have already.

Right, I always try to do that. One Ack that I did not include in v2
was the one you had on v1 24/24 (i.e. this patch). The reason I did
not add your Ack for v2 even on the patch where it obviously applied
was that I didn't know if you'd barf on the odev name.

But it was (and still is) a bit unclear if that was on Ack on the
last patch only, or if it was for the whole series? I think it might
have been for the whole series, but I'm not sure and I hate to be a
presumptuous idiot...

Cheers,
Peter

> -Daniel
>> Cheers,
>> Peter
>>
>>>
>>>>
>>>>> Anyway:
>>>>> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
>>>>
>>>> Thanks!
>>>>
>>>> Cheers,
>>>> Peter
>>>>
>>>>>  --
>>>>> Regards
>>>>> Andrzej
>>>>>
>>>>>>   * @funcs: control functions
>>>>>>   * @driver_private: pointer to the bridge driver's internal context
>>>>>>   */
>>>>>> @@ -271,6 +272,7 @@ struct drm_bridge {
>>>>>>    struct drm_bridge *next;
>>>>>>    struct list_head list;
>>>>>>    const struct drm_bridge_timings *timings;
>>>>>> +  struct device_link *link;
>>>>>>
>>>>>>    const struct drm_bridge_funcs *funcs;
>>>>>>    void *driver_private;
>>>>>
>>>>>
>>>>
>>>
>>
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> 
> 
>