On 23/02/16 14:03, Chris Wilson wrote:
On Tue, Feb 23, 2016 at 01:31:17PM +0000, Tvrtko Ursulin wrote:
On 23/02/16 13:06, Gabriel Feceoru wrote:
On 23.02.2016 13:05, Tvrtko Ursulin wrote:
Hi,
On 23/02/16 10:52, Gabriel Feceoru wrote:
Return error when I915_EXEC_BSD_RING2 flag is set but BSD2 ring
is not available in the HW.
What is the reasoning behind this? So far kernel was allowing userspace
to select these bits and execute on the first engine. With this patch it
would start failing potentially breaking userspace. Is it not too late
to make such change?
I noticed some inconsistencies in igt with regards to bsd and bsd1.
For instance, if bsd2 is not available, gem_sync@basic-bsd1 is skipped,
but it's skipped because of the 2nd check gem_has_bsd2 (see
gem_require_ring). Surprisingly gem_has_ring() didn't complain about bsd1.
This fix will make gem_has_ring() return false.
I'm not aware about legacy/compatibility issue - if that's the case,
please disregard this.
Hmmm.. Chris, what is the reasoning behind:
commit eaa03678b00179da89f194113c0740c033857c1c
Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Date: Thu Jan 28 13:44:19 2016 +0000
lib: Hide BSD1/BSD2 rings on hardware without BSD2
The kernel happily lets us run on I915_EXEC_BSD2 even with such hardware
existing. Sigh.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
diff --git a/lib/ioctl_wrappers.c b/lib/ioctl_wrappers.c
index 9dfa9b2603ce..fa44080e5902 100644
--- a/lib/ioctl_wrappers.c
+++ b/lib/ioctl_wrappers.c
@@ -1341,6 +1341,12 @@ static int gem_has_ring(int fd, int ring)
void gem_require_ring(int fd, int ring_id)
{
igt_require(gem_has_ring(fd, ring_id));
+
+ /* silly ABI, the kernel thinks everyone who has BSD also has BSD2 */
+ if ((ring_id & ~(3<<13)) == I915_EXEC_BSD) {
+ if (ring_id & (3 << 13))
+ igt_require(gem_has_bsd2(fd));
+ }
}
/* prime */
ABI was (and still is) that specifying BSD1 or BSD2 explicitly is
silently ignored by the kernel when BSD2 is not preset, defaulting
to BSD1.
Thereby pretending that BSD, BSD1, BSD2 exist.
This patch makes tests requesting BSD1 skip when there is no BSD2
which I think is wrong in any case.
BSD 1/2 selection only makes sense when we have multiple BSD rings.
Running tests on BSD default, BSD1 and BSD2 is pointless if they all
are equivalent. Using the BSD ping-pong when we have BSD1 and BSD2 is
questionable as the ping-pong nature is uncontrolled, but nevertheless
the code path needs to be tested.
If we want to (and can) change the ABI it should only reject the
non-existent ring and not limit the selection mechanism to
hardware which has BSD2.
I disagree, we have a ring selection mechanism. If the extension doesn't
exist, trying to use it should be an error. The extension was not only
an ABI mistake but undesired (it is now defunct).
Not sure that I understand what you meant here. Nothing as far as I can
tell is now defunct. Neither the selection mechanism, or the existence
of BSD2.
To be absolutely clear, you are, or you are not, in favour of Gabriel's
patch to start failing execbuf with fine grained BSD selection flags
when BSD2 is not present?
Regards,
Tvrtko
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