linux-kernel - Re: [PATCH v3 3/4] drm_dp_mst_topology: export two functions

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Message-ID: <CAJqEsoBtYCSRvjKWMBKPyHV8StXbxvJQeJB1tfYFbyLfmkpW8g@mail.gmail.com>
Date:   Fri, 5 Feb 2021 18:41:46 +1100
From:   Sam McNally <sammc@...omium.org>
To:     lyude@...hat.com
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Hans Verkuil <hverkuil@...all.nl>,
        Hans Verkuil <hans.verkuil@...co.com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 3/4] drm_dp_mst_topology: export two functions

On Tue, 2 Feb 2021 at 09:03, Lyude Paul <lyude@...hat.com> wrote:
>
> On Wed, 2020-09-23 at 12:13 +1000, Sam McNally wrote:
> > From: Hans Verkuil <hans.verkuil@...co.com>
> >
> > These are required for the CEC MST support.
> >
> > Signed-off-by: Hans Verkuil <hans.verkuil@...co.com>
> > Signed-off-by: Sam McNally <sammc@...omium.org>
> > ---
> >
> > (no changes since v1)
> >
> >  drivers/gpu/drm/drm_dp_mst_topology.c | 6 ++----
> >  include/drm/drm_dp_mst_helper.h       | 4 ++++
> >  2 files changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index 0d753201adbd..c783a2a1c114 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -62,8 +62,6 @@ struct drm_dp_pending_up_req {
> >  static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
> >                                   char *buf);
> >
> > -static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port);
> > -
> >  static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
> >                                      int id,
> >                                      struct drm_dp_payload *payload);
> > @@ -1864,7 +1862,7 @@ static void drm_dp_mst_topology_get_port(struct
> > drm_dp_mst_port *port)
> >   * drm_dp_mst_topology_try_get_port()
> >   * drm_dp_mst_topology_get_port()
> >   */
> > -static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
> > +void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
>
> Mhhhhhh-can you think of some way around this? I really don't think it's a good
> idea for us to be exposing topology references to things as-is, the thing is
> they're really meant to be used for critical sections in code where it'd become
> very painful to deal with an mst port disappearing from under us. Outside of MST
> helpers, everyone else should be dealing with the expectation that these things
> can disappear as a result of hotplugs at any moment.
>
> Note that we do expose malloc refs, but that's intentional as holding a malloc
> ref to something doesn't cause it to stay around even when it's unplugged - it
> just stops it from being unallocated.
>
>

Yes, it turns out we won't need this after all.

> >  {
> >         topology_ref_history_lock(port->mgr);
> >
> > @@ -1935,7 +1933,7 @@ drm_dp_mst_topology_get_port_validated_locked(struct
> > drm_dp_mst_branch *mstb,
> >         return NULL;
> >  }
> >
> > -static struct drm_dp_mst_port *
> > +struct drm_dp_mst_port *
> >  drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
> >                                        struct drm_dp_mst_port *port)
> >  {
> > diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> > index c7c79e0ced18..d036222e0d64 100644
> > --- a/include/drm/drm_dp_mst_helper.h
> > +++ b/include/drm/drm_dp_mst_helper.h
> > @@ -754,6 +754,10 @@ drm_dp_mst_detect_port(struct drm_connector *connector,
> >                        struct drm_dp_mst_topology_mgr *mgr,
> >                        struct drm_dp_mst_port *port);
> >
> > +struct drm_dp_mst_port *drm_dp_mst_topology_get_port_validated
> > +(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port);
> > +void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port);
> > +
> >  struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct
> > drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port);
> >
> >
>
> --
> Sincerely,
>    Lyude Paul (she/her)
>    Software Engineer at Red Hat
>
> Note: I deal with a lot of emails and have a lot of bugs on my plate. If you've
> asked me a question, are waiting for a review/merge on a patch, etc. and I
> haven't responded in a while, please feel free to send me another email to check
> on my status. I don't bite!
>