[PATCH 4/6] drm/xe/vf: Provide early access to GMDID register

[Matt Roper]

On Thu, May 23, 2024 at 09:22:38PM +0200, Michal Wajdeczko wrote:
> VFs do not have direct access to the GMDID register and must obtain
> its value from the GuC. Since we need GMDID value very early in the
> driver probe flow, before we even start the full setup of GT and GuC
> data structures, we must do some early initializations ourselves.
> 
> Additionally, since we also need GMDID for the media GT, which isn't
> created yet, temporarly tweak the root GT type into MEDIA to allow
> communication with the correct GuC, as only it can provide the value
> of the media GMDID register.
> 
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_pci.c | 47 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 44 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pci.c b/drivers/gpu/drm/xe/xe_pci.c
> index ece410289f6c..eefac633dbc1 100644
> --- a/drivers/gpu/drm/xe/xe_pci.c
> +++ b/drivers/gpu/drm/xe/xe_pci.c
> @@ -20,6 +20,8 @@
>  #include "xe_device.h"
>  #include "xe_drv.h"
>  #include "xe_gt.h"
> +#include "xe_gt_sriov_vf.h"
> +#include "xe_guc.h"
>  #include "xe_macros.h"
>  #include "xe_mmio.h"
>  #include "xe_module.h"
> @@ -471,10 +473,49 @@ static void read_gmdid(struct xe_device *xe, enum xe_gmdid_type type, u32 *ver,
>  
>  	KUNIT_STATIC_STUB_REDIRECT(read_gmdid, xe, type, ver, revid);
>  
> -	if (type == GMDID_MEDIA)
> -		gmdid_reg.addr += MEDIA_GT_GSI_OFFSET;
> +	if (IS_SRIOV_VF(xe)) {
> +		/*
> +		 * To get the value of the GMDID register, VFs must obtain it
> +		 * from the GuC using MMIO communication.
> +		 *
> +		 * Note that at this point the xe_gt is not fully uninitialized
> +		 * and only basic access to MMIO registers is possible. To use
> +		 * our existing GuC communication functions we must perform at
> +		 * least basic xe_gt and xe_guc initialization.
> +		 *
> +		 * Since to obtain the value of GMDID_MEDIA we need to use the
> +		 * media GuC, temporarly tweak the gt type.
> +		 */
> +		xe_gt_assert(gt, gt->info.type == XE_GT_TYPE_UNINITIALIZED);
> +
> +		if (type == GMDID_MEDIA) {
> +			gt->info.id = 1;
> +			gt->info.type = XE_GT_TYPE_MEDIA;
> +		} else {
> +			gt->info.id = 0;
> +			gt->info.type = XE_GT_TYPE_MAIN;
> +		}
> +
> +		xe_guc_comm_init_early(&gt->uc.guc);
> +
> +		/* don't bother with GMDID if failed to negotiate the GuC ABI */
> +		val = xe_gt_sriov_vf_bootstrap(gt) ? 0 : xe_gt_sriov_vf_gmdid(gt);
> +
> +		/* undo */
> +		gt->info.id = 0;
> +		gt->info.type = XE_GT_TYPE_UNINITIALIZED;

The xe_guc_comm_init_early() and xe_gt_sriov_vf_bootstrap() above also
make changes to the various GuC0 structures (which might be "wrong" if
we were reading the media's GMD_ID, but I think all of those changes
wind up getting overwritten later with the correct GuC0 values again
later when we initialize the GuC for real.  You might want to add some
kind of comment about that, since otherwise it looks at first glance
like we might be leaving GuC1 state inside the GuC0 structure here.

Otherwise,

        Reviewed-by: Matt Roper <matthew.d.roper at intel.com>

> +	} else {
> +		/*
> +		 * We need to apply the GSI offset explicitly here as at this
> +		 * point the xe_gt is not fully uninitialized and only basic
> +		 * access to MMIO registers is possible.
> +		 */
> +		if (type == GMDID_MEDIA)
> +			gmdid_reg.addr += MEDIA_GT_GSI_OFFSET;
> +
> +		val = xe_mmio_read32(gt, gmdid_reg);
> +	}
>  
> -	val = xe_mmio_read32(gt, gmdid_reg);
>  	*ver = REG_FIELD_GET(GMD_ID_ARCH_MASK, val) * 100 + REG_FIELD_GET(GMD_ID_RELEASE_MASK, val);
>  	*revid = REG_FIELD_GET(GMD_ID_REVID, val);
>  }
> -- 
> 2.43.0
> 

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