On Wed, May 18, 2016 at 10:18:52AM +0100, Jon Hunter wrote:
>
> On 17/05/16 18:36, Daniel Vetter wrote:
> > On Tue, May 17, 2016 at 7:29 PM, Jon Hunter <jonathanh@xxxxxxxxxx> wrote:
> >>>> @@ -764,6 +769,9 @@ tegra_dsi_connector_duplicate_state(struct drm_connector *connector)
> >>>> if (!copy)
> >>>> return NULL;
> >>>>
> >>>> + if (copy->base.crtc)
> >>>> + drm_connector_reference(connector);
> >>>> +
> >>>
> >>> Please use __drm_atomic_helper_connector_duplicate_state instead of
> >>> open-coding it.
> >>
> >> Unfortunately, tegra is allocating and duplicating memory for the entire
> >> tegra_dsi_state structure (of which drm_connector_state is a member) in
> >> this function and so I was not able to do that. However, may be Thierry
> >> can comment on whether that is completely necessary and if we can move
> >> to using __drm_atomic_helper_connector_duplicate_state() instead.
> >
> > Check out how other drivers are using this helper - it is explicitly
> > for the case where you duplicate the entire struct, and it just
> > initializes the core part from drm. You can then add your own fixup
> > code afterwards. It also doesn't matter whether you do kmalloc or
> > kcalloc or kmemdup - it does a memcpy of its own to make sure state
> > gets copied.
>
> I had a look but I don't see anyone using the
> __drm_atomic_helper_connector_duplicate_state() helper, I only see that
> drivers are using drm_atomic_helper_connector_duplicate_state()
> directly.
>
> Yes I understand that this helper is doing an explicit copy of the
> entire drm_connector_state struct and yes I could do something like the
> following ...
>
> static struct drm_connector_state *
> tegra_dsi_connector_duplicate_state(struct drm_connector *connector)
> {
> struct tegra_dsi_state *state = to_dsi_state(connector->state);
> struct tegra_dsi_state *copy;
>
> copy = kmemdup(state, sizeof(*state), GFP_KERNEL);
> if (!copy)
> return NULL;
>
> __drm_atomic_helper_connector_duplicate_state(connector,
> ©->base);
>
> return ©->base;
> }
>
> ... however, this means that I am copying the drm_connector_state twice
> and this is what I was trying to avoid. Sorry if I am misunderstanding
> you here, but I don't see how I can avoid the 2nd copy if I use
> __drm_atomic_helper_connector_duplicate_state().
The copying twice should be harmless - this function is only called when
changing connector states, i.e. full modeset. And modesets aren't fast
anyway.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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