Re: [PATCH v2 2/2] drm/i915/icl: Add IOCTL for getting MOCS table version

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On 22/10/18 10:13, Tomasz Lis wrote:
For Icelake and above, MOCS table for each platform is published
within bspec. The table is versioned, and new entries are assigned
a version number. Existing entries do not change and their version
is constant.

This introduces a parameter which allows getting max version number
of the MOCS entries currently supported, ie. value of 2 would mean
only version 1 and version 2 entries are initialized and can be used
by the user mode clients.

BSpec: 34007
Signed-off-by: Tomasz Lis <tomasz.lis@xxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
Cc: Zhi A Wang <zhi.a.wang@xxxxxxxxx>
Cc: Anuj Phogat <anuj.phogat@xxxxxxxxx>
---
  drivers/gpu/drm/i915/i915_drv.c   |  6 ++++++
  drivers/gpu/drm/i915/intel_mocs.c | 12 ++++++++++++
  drivers/gpu/drm/i915/intel_mocs.h |  1 +
  include/uapi/drm/i915_drm.h       | 11 +++++++++++
  4 files changed, 30 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index baac35f..92fa8fd 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -53,6 +53,7 @@
  #include "i915_vgpu.h"
  #include "intel_drv.h"
  #include "intel_uc.h"
+#include "intel_mocs.h"
static struct drm_driver driver; @@ -444,6 +445,11 @@ static int i915_getparam_ioctl(struct drm_device *dev, void *data,
  	case I915_PARAM_MMAP_GTT_COHERENT:
  		value = INTEL_INFO(dev_priv)->has_coherent_ggtt;
  		break;
+	case I915_PARAM_MOCS_TABLE_VERSION:
+		value = intel_mocs_table_version(dev_priv);
+		if (!value)
+			return -ENODEV;

Do we really want to return -ENODEV for platforms that do have a MOCS table programmed, but the table is not one versioned in the specs (i.e. Gen9-10)? I think returning "0" for those to indicate "kernel-defined table" would be ok and we could limit -ENODEV for platforms that don't have a table at all. But what wins is what the callers of the ioctl would like to get from the kernel ;)

+		break;
  	default:
  		DRM_DEBUG("Unknown parameter %d\n", param->param);
  		return -EINVAL;
diff --git a/drivers/gpu/drm/i915/intel_mocs.c b/drivers/gpu/drm/i915/intel_mocs.c
index dc34e83..fc1e98b 100644
--- a/drivers/gpu/drm/i915/intel_mocs.c
+++ b/drivers/gpu/drm/i915/intel_mocs.c
@@ -469,6 +469,18 @@ static i915_reg_t mocs_register(enum intel_engine_id engine_id, int index)
  }
/**
+ * intel_mocs_table_version() - get version of mocs table implementation
+ * @i915: i915 device struct.
+ */
+int intel_mocs_table_version(struct drm_i915_private *i915)
+{
+	if (IS_ICELAKE(i915))
+		return 1;

Can we add this version value as a define above the table, to keep them close to each other?

If we agree on my suggestion above to differentiate between no table at all (< 0), kernel-defined table (= 0) and spec-defined versioned table (> 0), it might also be useful to store the version with the table info in drm_i915_mocs_table and then have intel_mocs_table_version call get_mocs_settings(), e.g:

int intel_mocs_table_version(struct drm_i915_private *i915)
{
	struct drm_i915_mocs_table table;

	if (!get_mocs_settings(i915, &table))
		return -ENODEV;

	return table->version;
}

Thanks,
Daniele

+	else
+		return 0;
+}
+
+/**
   * intel_mocs_init_engine() - emit the mocs control table
   * @engine:	The engine for whom to emit the registers.
   *
diff --git a/drivers/gpu/drm/i915/intel_mocs.h b/drivers/gpu/drm/i915/intel_mocs.h
index d89080d..dc1d64a 100644
--- a/drivers/gpu/drm/i915/intel_mocs.h
+++ b/drivers/gpu/drm/i915/intel_mocs.h
@@ -55,5 +55,6 @@
  int intel_rcs_context_init_mocs(struct i915_request *rq);
  void intel_mocs_init_l3cc_table(struct drm_i915_private *dev_priv);
  void intel_mocs_init_engine(struct intel_engine_cs *engine);
+int intel_mocs_table_version(struct drm_i915_private *i915);
#endif
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 298b2e1..16aafc4 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -559,6 +559,17 @@ typedef struct drm_i915_irq_wait {
   */
  #define I915_PARAM_MMAP_GTT_COHERENT	52
+/*
+ * Query MOCS table version used during hardware initialization.
+ *
+ * The MOCS table for each platform is published as part of bspec. Entries in
+ * the table are supposed to never be modified, but new enties are added, making
+ * more indexes in the table valid. This parameter informs which version
+ * of the table was used to initialize the currently used graphics hardware,
+ * and therefore which MOCS indexes are useable.
+ */
+#define I915_PARAM_MOCS_TABLE_VERSION	53
+
  typedef struct drm_i915_getparam {
  	__s32 param;
  	/*

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