Woops, this should have gone to the Xe list, not the i915 list. I'll
re-send.
Matt
On Mon, Aug 12, 2024 at 11:07:37AM -0700, Matt Roper wrote:
> Early in the development of Xe we identified an issue with SVG state
> handling on DG2 and MTL (and later on Xe2 as well). In
> commit 72ac304769dd ("drm/xe: Emit SVG state on RCS during driver load
> on DG2 and MTL") and commit fb24b858a20d ("drm/xe/xe2: Update SVG state
> handling") we implemented our own workaround to prevent SVG state from
> leaking from context A to context B in cases where context B never
> issues a specific state setting.
>
> The hardware teams have now created official workaround Wa_14019789679
> to cover this issue. The workaround description only requires emitting
> 3DSTATE_MESH_CONTROL, since they believe that's the only SVG instruction
> that would potentially remain unset by a context B, but still cause
> notable issues if unwanted values were inherited from context A.
> However since we already have a more extensive implementation that emits
> the entire SVG state and prevents _any_ SVG state from unintentionally
> leaking, we'll stick with our existing implementation just to be safe.
>
> Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
> ---
> drivers/gpu/drm/xe/xe_lrc.c | 35 +++++++++++++++++++++---------
> drivers/gpu/drm/xe/xe_wa_oob.rules | 2 ++
> 2 files changed, 27 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_lrc.c b/drivers/gpu/drm/xe/xe_lrc.c
> index 58121821f081..974a9cd8c379 100644
> --- a/drivers/gpu/drm/xe/xe_lrc.c
> +++ b/drivers/gpu/drm/xe/xe_lrc.c
> @@ -5,6 +5,8 @@
>
> #include "xe_lrc.h"
>
> +#include <generated/xe_wa_oob.h>
> +
> #include <linux/ascii85.h>
>
> #include "instructions/xe_mi_commands.h"
> @@ -24,6 +26,7 @@
> #include "xe_memirq.h"
> #include "xe_sriov.h"
> #include "xe_vm.h"
> +#include "xe_wa.h"
>
> #define LRC_VALID BIT_ULL(0)
> #define LRC_PRIVILEGE BIT_ULL(8)
> @@ -1581,19 +1584,31 @@ void xe_lrc_emit_hwe_state_instructions(struct xe_exec_queue *q, struct xe_bb *b
> int state_table_size = 0;
>
> /*
> - * At the moment we only need to emit non-register state for the RCS
> - * engine.
> + * Wa_14019789679
> + *
> + * If the driver doesn't explicitly emit the SVG instructions while
> + * setting up the default LRC, the context switch will write 0's
> + * (noops) into the LRC memory rather than the expected instruction
> + * headers. Application contexts start out as a copy of the default
> + * LRC, and if they also do not emit specific settings for some SVG
> + * state, then on context restore they'll unintentionally inherit
> + * whatever state setting the previous context had programmed into the
> + * hardware (i.e., the lack of a 3DSTATE_* instruction in the LRC will
> + * prevent the hardware from resetting that state back to any specific
> + * value).
> + *
> + * The official workaround only requires emitting 3DSTATE_MESH_CONTROL
> + * since that's a specific state setting that can easily cause GPU
> + * hangs if unintentionally inherited. However to be safe we'll
> + * continue to emit all of the SVG state since it's best not to leak
> + * any of the state between contexts, even if that leakage is harmless.
> */
> - if (q->hwe->class != XE_ENGINE_CLASS_RENDER)
> - return;
> -
> - switch (GRAPHICS_VERx100(xe)) {
> - case 1255:
> - case 1270 ... 2004:
> + if (XE_WA(gt, 14019789679) && q->hwe->class == XE_ENGINE_CLASS_RENDER) {
> state_table = xe_hpg_svg_state;
> state_table_size = ARRAY_SIZE(xe_hpg_svg_state);
> - break;
> - default:
> + }
> +
> + if (!state_table) {
> xe_gt_dbg(gt, "No non-register state to emit on graphics ver %d.%02d\n",
> GRAPHICS_VER(xe), GRAPHICS_VERx100(xe) % 100);
> return;
> diff --git a/drivers/gpu/drm/xe/xe_wa_oob.rules b/drivers/gpu/drm/xe/xe_wa_oob.rules
> index 5cf27ff27ce6..920ca5060146 100644
> --- a/drivers/gpu/drm/xe/xe_wa_oob.rules
> +++ b/drivers/gpu/drm/xe/xe_wa_oob.rules
> @@ -35,3 +35,5 @@
> GRAPHICS_VERSION(2001)
> 22019338487_display PLATFORM(LUNARLAKE)
> 16023588340 GRAPHICS_VERSION(2001)
> +14019789679 GRAPHICS_VERSION(1255)
> + GRAPHICS_VERSION_RANGE(1270, 2004)
> --
> 2.45.2
>
--
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation
