[Intel-xe] [PATCH] drm/xe: Add fake workaround to maintain backward compatible in MI_BATCH_BUFFER_START

[Lucas De Marchi]

On Sun, Jan 29, 2023 at 01:30:44PM -0800, Jose Souza wrote:
>i915 has the same fake workaround to return MI_BATCH_BUFFER_START
>nested batch buffer behavior in DG2 and newer platforms to the same
>behavior as older platforms.
>
>So here cleaning up TGL_NESTED_BB_EN in MI_MODE to disable third level
>chained batch buffer level.
>
>Bspec: 45974, 45718
>Cc: Matt Roper <matthew.d.roper at intel.com>
>Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
>---
> drivers/gpu/drm/xe/xe_rtp_types.h |  2 ++
> drivers/gpu/drm/xe/xe_wa.c        | 11 +++++++++++
> 2 files changed, 13 insertions(+)
>
>diff --git a/drivers/gpu/drm/xe/xe_rtp_types.h b/drivers/gpu/drm/xe/xe_rtp_types.h
>index 14e5d4dbb4c15..72f3e2e83014f 100644
>--- a/drivers/gpu/drm/xe/xe_rtp_types.h
>+++ b/drivers/gpu/drm/xe/xe_rtp_types.h
>@@ -52,6 +52,8 @@ enum {
> 	XE_RTP_MATCH_FUNC,
> };
>
>+#define IP_VERSION_FOREVER 9900

there is already a define for this in this header.

>+
> /** struct xe_rtp_rule - match rule for processing entry */
> struct xe_rtp_rule {
> 	u8 match_type;
>diff --git a/drivers/gpu/drm/xe/xe_wa.c b/drivers/gpu/drm/xe/xe_wa.c
>index 3325de3edf691..3616b2284d186 100644
>--- a/drivers/gpu/drm/xe/xe_wa.c
>+++ b/drivers/gpu/drm/xe/xe_wa.c
>@@ -285,6 +285,17 @@ static const struct xe_rtp_entry lrc_was[] = {
> 		     DG1_HZ_READ_SUPPRESSION_OPTIMIZATION_DISABLE,
> 		     XE_RTP_FLAG(MASKED_REG))
> 	},
>+	{ XE_RTP_NAME("FakeWaDisableNestedBBMode"),
>+	  /*
>+	   * This is a "fake" workaround defined by software to ensure we
>+	   * maintain reliable, backward-compatible behavior for userspace with
>+	   * regards to how nested MI_BATCH_BUFFER_START commands are handled.
>+	   */
>+	  XE_RTP_RULES(GRAPHICS_VERSION_RANGE(1255, IP_VERSION_FOREVER)),
>+	  XE_RTP_CLR(RING_MI_MODE(0),
>+		     TGL_NESTED_BB_EN,
>+		     XE_RTP_FLAG(MASKED_REG, ENGINE_BASE))
>+	},

this conflicts with the changesto allow multiple actions in a
single entry, but should be easy to fix.

I think we can leave this wa here, but until now we tried not to mix WAs
with normal programming of the driver. Maybe just add a different table
like lrc_additional_programming[]?

Lucas De Marchi