On Wed, Oct 17, 2012 at 8:47 PM, Eric Anholt <eric at anholt.net> wrote: > Chris Wilson <chris at chris-wilson.co.uk> writes: > >> With the introduction of per-process GTT space, the hardware designers >> thought it wise to also limit the ability to write to MMIO space to only >> a "secure" batch buffer. The ability to rewrite registers is the only >> way to program the hardware to perform certain operations like scanline >> waits (required for tear-free windowed updates). So we either have a >> choice of adding an interface to perform those synchronized updates >> inside the kernel, or we permit certain processes the ability to write >> to the "safe" registers from within its command stream. This patch >> exposes the ability to submit a SECURE batch buffer to >> DRM_ROOT_ONLY|DRM_MASTER processes. > > This seems like a major blow to ever getting non-root X. Currently we only need this to get scanline waits going on snb+ and on ivb+ that will neatly keep the gpu out of rc6 while waiting for that scanline. So there rather clearly a massive legacy feature, ill supported by the hw. So that's the only thing that the X driver will lose, to which I highly suggest to simply install a pageflipping compositor of sorts and call it a day. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
