drm/xe/uapi: Add support for CPU caching mode

Allow userspace to specify the CPU caching mode at object creation.
Modify gem create handler and introduce xe_bo_create_user to replace
xe_bo_create. In a later patch we will support setting the pat_index as
part of vm_bind, where expectation is that the coherency mode extracted
from the pat_index must be least 1way coherent if using cpu_caching=wb.

v2
  - s/smem_caching/smem_cpu_caching/ and
    s/XE_GEM_CACHING/XE_GEM_CPU_CACHING/. (Matt Roper)
  - Drop COH_2WAY and just use COH_NONE + COH_AT_LEAST_1WAY; KMD mostly
    just cares that zeroing/swap-in can't be bypassed with the given
    smem_caching mode. (Matt Roper)
  - Fix broken range check for coh_mode and smem_cpu_caching and also
    don't use constant value, but the already defined macros. (José)
  - Prefer switch statement for smem_cpu_caching -> ttm_caching. (José)
  - Add note in kernel-doc for dgpu and coherency modes for system
    memory. (José)
v3 (José):
  - Make sure to reject coh_mode == 0 for VRAM-only.
  - Also make sure to actually pass along the (start, end) for
    __xe_bo_create_locked.
v4
  - Drop UC caching mode. Can be added back if we need it. (Matt Roper)
  - s/smem_cpu_caching/cpu_caching. Idea is that VRAM is always WC, but
    that is currently implicit and KMD controlled. Make it explicit in
    the uapi with the limitation that it currently must be WC. For VRAM
    + SYS objects userspace must now select WC. (José)
  - Make sure to initialize bo_flags. (José)
v5
  - Make to align with the other uapi and prefix uapi constants with
    DRM_ (José)
v6:
  - Make it clear that zero cpu_caching is only allowed for kernel
    objects. (José)
v7: (Oak)
  - With all the changes from the original design, it looks we can
    further simplify here and drop the explicit coh_mode. We can just
    infer the coh_mode from the cpu_caching. i.e reject cpu_caching=wb +
    coh_none. It's one less thing for userspace to maintain so seems
    worth it.
v8:
  - Make sure to also update the kselftests.

Testcase: igt@xe_mmap@cpu-caching
Signed-off-by: Pallavi Mishra <pallavi.mishra@intel.com>
Co-developed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Filip Hazubski <filip.hazubski@intel.com>
Cc: Carl Zhang <carl.zhang@intel.com>
Cc: Effie Yu <effie.yu@intel.com>
Cc: Zhengguo Xu <zhengguo.xu@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Cc: Oak Zeng <oak.zeng@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: Zhengguo Xu <zhengguo.xu@intel.com>
Acked-by: Bartosz Dunajski <bartosz.dunajski@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
index 88f3aca02b08..ab7d1b26c773 100644
--- a/include/uapi/drm/xe_drm.h
+++ b/include/uapi/drm/xe_drm.h
@@ -541,8 +541,25 @@ struct drm_xe_gem_create {
 	 */
 	__u32 handle;
 
+	/**
+	 * @cpu_caching: The CPU caching mode to select for this object. If
+	 * mmaping the object the mode selected here will also be used.
+	 *
+	 * Supported values:
+	 *
+	 * DRM_XE_GEM_CPU_CACHING_WB: Allocate the pages with write-back
+	 * caching.  On iGPU this can't be used for scanout surfaces. Currently
+	 * not allowed for objects placed in VRAM.
+	 *
+	 * DRM_XE_GEM_CPU_CACHING_WC: Allocate the pages as write-combined. This
+	 * is uncached. Scanout surfaces should likely use this. All objects
+	 * that can be placed in VRAM must use this.
+	 */
+#define DRM_XE_GEM_CPU_CACHING_WB                      1
+#define DRM_XE_GEM_CPU_CACHING_WC                      2
+	__u16 cpu_caching;
 	/** @pad: MBZ */
-	__u32 pad;
+	__u16 pad;
 
 	/** @reserved: Reserved */
 	__u64 reserved[2];