On Wed, 13 Oct 2004 10:13:50 +0100, Keith Whitwell <[EMAIL PROTECTED]> wrote:
Felix K�hling wrote: I think the reason that you are experiencing failures is because the X server is trying to read or poll the drm filehandle, but Jon has recently changed the behaviour of that filehandle to return an error on those operations, rather than indicating that no bytes are pending.
Let me stress that in most drivers there is no need for the X server to be looking at this filehandle at all, but the code which does so is widely distributed and this change to the DRM will break it.
Is it the poll() call that is the problem? I can set it back to returning zero. The kernel people are saying this is wrong and are pushing me to have it return (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM) which is the correct return for an unimplemented poll function.
In the very beginning, shared code in the X server listened to this fd, and shared code in the DRM existed to write to this fd, at the possible request of device-dependent DRM code. The first DRM driver, the gamma, used this mechanism for context switching. But no other DRM driver except perhaps ffb ever has.
About 18 months ago, I recognized this and pushed the shared code into the gamma driver, and removed the poll() and read() functions from drm_fops.h. Within the day I recognized that the X server continued to examine the fd, and that there was a need to restore empty poll() and read() functions. Now that the gamma driver is dead, maybe we can go about pulling that behaviour out of the X server shared code as well. But right now, you have a situation where everybody running a DRI-enabled X server is dependent on the poll() (and maybe read()) function behaving in the way it always has.
So, it's not really an unimplemented poll() function, but the backwards-compatible ghost of a real communications channel which is still polled, but never written to.
Keith
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