On Fri, Jan 12, 2018 at 10:40:16AM +0000, Chris Wilson wrote: > Quoting Thierry Reding (2018-01-11 22:22:46) > > From: Thierry Reding <tred...@nvidia.com> > > > > This set of patches adds support for fences to Tegra DRM and complements > > the fence FD support for Nouveau. Technically this isn't necessary for a > > fence-based synchronization loop with Nouveau because the KMS core takes > > care of all that, but engines behind host1x can use the IOCTL extensions > > provided here to emit fence FDs that in turn can be used to synchronize > > their jobs with either the scanout engine or the GPU. > > Whilst hooking up fences, I advise you to also hook up drm_syncobj. > Internally they each resolve to another fence, so the mechanics are > identical, you just need another array in the uABI for in/out syncobj. > The advantage of drm_syncobj is that userspace can track internal fences > using inexhaustible handles, reserving the precious fd for IPC or KMS.
I'm not sure that I properly understand how to use these. It looks as if
they are better fence FDs, so in case where you submit internal work you
would go with a drm_syncobj and when you need access to the fence from a
different process or driver, you should use an FD.
Doesn't this mean we can cover this by just adding a flag that marks the
fence as being a handle or an FD? Do we have situations where we want an
FD *and* a handle returned as result of the job submission?
For the above it would suffice to add two additional flags:
#define DRM_TEGRA_SUBMIT_WAIT_SYNCOBJ (1 << 2)
#define DRM_TEGRA_SUBMIT_EMIT_SYNCOBJ (1 << 3)
which would even allow both to be combined:
DRM_TEGRA_SUBMIT_WAIT_SYNCOBJ | DRM_TEGRA_SUBMIT_EMIT_FENCE_FD
would allow the job to wait for an internal syncobj (defined by handle
in the fence member) and return a fence (as FD in the fence member) to
pass on to another process or driver as prefence.
Thierry
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