[Intel-xe] [PATCH v2] drm/xe: Add fake workaround to maintain backward compatible in MI_BATCH_BUFFER_START

[Matt Roper]

On Mon, Jan 30, 2023 at 08:17:23AM -0800, José Roberto de 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.

I was kind of assuming we'd just drop this setting for the Xe driver.  I
believe hardware will be removing the option to turn off nested
batchbuffers in an upcoming platform, so userspace is going to have to
adapt to the new behavior soon anyway; doing it while moving to a new
KMD seems like the easiest time to make that happen since the UMDs are
already updating their programming models.


Matt

> 
> v2:
> - replace IP_VERSION_FOREVER by XE_RTP_END_VERSION_UNDEFINED
> - move fake workaround to lrc_additional_programming table
> 
> Bspec: 45974, 45718
> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
> 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_gt.c |  1 +
>  drivers/gpu/drm/xe/xe_wa.c | 28 ++++++++++++++++++++++++++++
>  drivers/gpu/drm/xe/xe_wa.h |  1 +
>  3 files changed, 30 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt.c b/drivers/gpu/drm/xe/xe_gt.c
> index 84a73eeccd297..5d07e1e7bd506 100644
> --- a/drivers/gpu/drm/xe/xe_gt.c
> +++ b/drivers/gpu/drm/xe/xe_gt.c
> @@ -311,6 +311,7 @@ int xe_gt_record_default_lrcs(struct xe_gt *gt)
>  
>  		xe_reg_sr_init(&hwe->reg_lrc, "LRC", xe);
>  		xe_wa_process_lrc(hwe);
> +		xe_wa_process_lrc_additional_programming(hwe);
>  
>  		default_lrc = drmm_kzalloc(&xe->drm,
>  					   xe_lrc_size(xe, hwe->class),
> diff --git a/drivers/gpu/drm/xe/xe_wa.c b/drivers/gpu/drm/xe/xe_wa.c
> index 3325de3edf691..744b7d0982683 100644
> --- a/drivers/gpu/drm/xe/xe_wa.c
> +++ b/drivers/gpu/drm/xe/xe_wa.c
> @@ -288,6 +288,21 @@ static const struct xe_rtp_entry lrc_was[] = {
>  	{}
>  };
>  
> +static const struct xe_rtp_entry lrc_additional_programming[] = {
> +	{ 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, XE_RTP_END_VERSION_UNDEFINED)),
> +	  XE_RTP_CLR(RING_MI_MODE(0),
> +		     TGL_NESTED_BB_EN,
> +		     XE_RTP_FLAG(MASKED_REG, ENGINE_BASE))
> +	},
> +	{}
> +};
> +
>  static const struct xe_rtp_entry register_whitelist[] = {
>  	{ XE_RTP_NAME("WaAllowPMDepthAndInvocationCountAccessFromUMD, 1408556865"),
>  	  XE_RTP_RULES(GRAPHICS_VERSION_RANGE(1200, 1210), ENGINE_CLASS(RENDER)),
> @@ -362,6 +377,19 @@ void xe_wa_process_lrc(struct xe_hw_engine *hwe)
>  	xe_rtp_process(lrc_was, &hwe->reg_lrc, hwe->gt, hwe);
>  }
>  
> +/**
> + * xe_wa_process_lrc_additional_programming - process additional LRC programming
> + * table
> + * @hwe: engine instance to process workarounds for
> + *
> + * Process additional context programming table for this platform, saving in
> + * @hwe all the registers changes that need to be applied on context restore.
> + */
> +void xe_wa_process_lrc_additional_programming(struct xe_hw_engine *hwe)
> +{
> +	xe_rtp_process(lrc_additional_programming, &hwe->reg_lrc, hwe->gt, hwe);
> +}
> +
>  /**
>   * xe_reg_whitelist_process_engine - process table of registers to whitelist
>   * @hwe: engine instance to process whitelist for
> diff --git a/drivers/gpu/drm/xe/xe_wa.h b/drivers/gpu/drm/xe/xe_wa.h
> index 1a0659690a320..872f3e4ddc73c 100644
> --- a/drivers/gpu/drm/xe/xe_wa.h
> +++ b/drivers/gpu/drm/xe/xe_wa.h
> @@ -12,6 +12,7 @@ struct xe_hw_engine;
>  void xe_wa_process_gt(struct xe_gt *gt);
>  void xe_wa_process_engine(struct xe_hw_engine *hwe);
>  void xe_wa_process_lrc(struct xe_hw_engine *hwe);
> +void xe_wa_process_lrc_additional_programming(struct xe_hw_engine *hwe);
>  
>  void xe_reg_whitelist_process_engine(struct xe_hw_engine *hwe);
>  void xe_reg_whitelist_apply(struct xe_hw_engine *hwe);
> -- 
> 2.39.1
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation