Re: [PATCH 2/3] drm/tegra: Deliver syncpoint base to user space

[Arto Merilainen]

On 10/11/2013 12:43 PM, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Wed, Oct 09, 2013 at 02:54:09PM +0300, Arto Merilainen wrote:
> > This patch makes the necessary additions to deliver syncpoint base
> > to the user space.
> >
> > This patch splits the index field in the drm_tegra_get_syncpt structure
> > into three separate fields (index, support_base, base_id). This allows
> > to keep compatibility over kernel versions:
> > - The placing of index field stays constant and therefore the interface
> >    should stay compatible with earlier userspace versions.
> > - The old index field was input-only and it was not supposed to be read
> >    afterwards. Delivering data back in the same field should not introduce
> >    regressions to any old user space applications.
> > - Old kernels left support_base and base_id fields intact (zero) and
> >    hence the new user space applications get the correct response from
> >    the kernel (=syncpoint does not have a base).
> >
> > Signed-off-by: Arto Merilainen <amerilainen@xxxxxxxxxx>
> > ---
> >   drivers/gpu/host1x/drm/drm.c | 2 ++
> >   include/uapi/drm/tegra_drm.h | 4 +++-
> >   2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/host1x/drm/drm.c b/drivers/gpu/host1x/drm/drm.c
> > index 8c61cee..4251563 100644
> > --- a/drivers/gpu/host1x/drm/drm.c
> > +++ b/drivers/gpu/host1x/drm/drm.c
> > @@ -468,6 +468,8 @@ static int tegra_get_syncpt(struct drm_device *drm, void *data,
> >
> >   	syncpt = context->client->syncpts[args->index];
> >   	args->id = host1x_syncpt_id(syncpt);
> > +	args->support_base = syncpt->base ? 1 : 0;
> > +	args->base_id = syncpt->base ? syncpt->base->id : 0;
> >
> >   	return 0;
> >   }
> > diff --git a/include/uapi/drm/tegra_drm.h b/include/uapi/drm/tegra_drm.h
> > index 73bde4e..7a79ca5 100644
> > --- a/include/uapi/drm/tegra_drm.h
> > +++ b/include/uapi/drm/tegra_drm.h
> > @@ -61,7 +61,9 @@ struct drm_tegra_close_channel {
> >
> >   struct drm_tegra_get_syncpt {
> >   	__u64 context;
> > -	__u32 index;
> > +	__u16 index;
> > +	__u8 support_base;
> > +	__u8 base_id;
> >   	__u32 id;
>
> I don't like this. Can't we just add a separate IOCTL? Something like:

Sure. This felt like a good idea, but I must admit I had a bit mixed 
feelings after looking my own explanation why this would be ok...

- Arto

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