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

[Daniel Vetter]

On Mon, May 14, 2018 at 10:40 PM, Peter Rosin <peda@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>>> ---
>>>>>  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.
-Daniel
> Cheers,
> Peter
>
>>
>>>
>>>> Anyway:
>>>> Reviewed-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
>>>
>>> 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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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch