Quoting Mika Kuoppala (2019-11-13 15:49:08)
> From: Jon Bloomfield <jon.bloomfield@xxxxxxxxx>
>
> gen9+ introduces a cmdparser for the BLT engine which copies the
> incoming BB to a kmd owned buffer for submission (to prevent changes
> being made after the bb has been safely scanned). This breaks the
> spin functionality because it relies on changing the submitted spin
> buffers in order to terminate them.
>
> Instead, for gen9+, we change the semantics by introducing a COND_BB_END
> into the infinite loop, to wait until a memory flag (in anothe bo) is
> cleared.
>
> v2: Correct nop length to avoid overwriting bb_end instr when using
> a dependency bo (cork)
> v3: fix conflicts on igt_dummyload (Mika)
> v4: s/bool running/uint32_t running, fix r->delta (Mika)
> v5: remove overzealous assert (Mika)
> v6: rebase on top of lib changes (Mika)
> v7: rework on top of public igt lib changes (Mika)
> v8: rebase
>
> Signed-off-by: Jon Bloomfield <jon.bloomfield@xxxxxxxxx> (v2)
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> lib/i830_reg.h | 2 +-
> lib/igt_dummyload.c | 46 +++++++++++++++++++++++--
> lib/igt_dummyload.h | 3 ++
> lib/intel_reg.h | 3 ++
> tests/i915/gem_double_irq_loop.c | 2 --
> tests/i915/gem_write_read_ring_switch.c | 2 +-
> 6 files changed, 52 insertions(+), 6 deletions(-)
>
> diff --git a/lib/i830_reg.h b/lib/i830_reg.h
> index a57691c7..41020256 100644
> --- a/lib/i830_reg.h
> +++ b/lib/i830_reg.h
> @@ -43,7 +43,7 @@
> /* broadwater flush bits */
> #define BRW_MI_GLOBAL_SNAPSHOT_RESET (1 << 3)
>
> -#define MI_COND_BATCH_BUFFER_END (0x36<<23 | 1)
> +#define MI_COND_BATCH_BUFFER_END (0x36 << 23)
> #define MI_DO_COMPARE (1<<21)
>
> #define MI_BATCH_BUFFER_END (0xA << 23)
> diff --git a/lib/igt_dummyload.c b/lib/igt_dummyload.c
> index c079bd04..a88c8582 100644
> --- a/lib/igt_dummyload.c
> +++ b/lib/igt_dummyload.c
> @@ -130,7 +130,15 @@ emit_recursive_batch(igt_spin_t *spin,
> spin->poll_handle = poll->handle;
> execbuf->buffer_count++;
>
> - if (opts->flags & IGT_SPIN_POLL_RUN) {
> + /*
> + * For gen9+ we use a conditional loop rather than an
> + * infinite loop, because we are unable to modify the
> + * BB's once they have been scanned by the cmdparser
> + * We share the poll buffer for the conditional test
> + * and is always the first buffer in the batch list
> + */
> +
> + if (gen >= 9 || (opts->flags & IGT_SPIN_POLL_RUN)) {
Nah, you could just sample the batch buffer rather than always adding
the poll buffer (since the cmdparser implicitly creates the second buffer
for you). Using the comparison value of MI_BATCH_BUFFER_END you wouldn't
even have to worry about altering callers.
-Chris
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