[Intel-gfx] [PATCH 1/8] drm/i915/gen9: Add framework to whitelist specific GPU registers

Arun Siluvery arun.siluvery at linux.intel.com
Wed Jan 13 02:06:26 PST 2016

Some of the HW registers are privileged and cannot be written to from a
non-privileged batch buffers coming from userspace unless they are on whitelist.
Userspace need write access to them to implement preemption related WA.

The reason for using this approach is, the register bits that control preemption
granularity at the HW level are not context save/restored; so even if we set these
bits always in kernel they are going to change once the context is switched out.
We can consider making them non-privileged by default but these registers also
contain other chicken bits which should not be allowed to be modified.

In the later revisions controlling bits are save/restored at context level but
in the existing revisions these are exported via other debug registers and should
be on the whitelist. This patch adds changes to provide HW with a list of registers
to be whitelisted. HW checks this list during execution and provides access accordingly.

HW imposes a limit on the number of registers on whitelist and it is per-engine.
At this point we are only enabling whitelist for RCS and we don't foresee any
requirement for other engines.

The registers to be whitelisted are added using generic workaround list mechanism,
even these are only enablers for userspace workarounds. But by sharing this
mechanism we get some test assets without additional cost (Mika).

v2: rebase

Reviewed-by: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Signed-off-by: Arun Siluvery <arun.siluvery at linux.intel.com>
 drivers/gpu/drm/i915/i915_drv.h         |  9 ++++++++-
 drivers/gpu/drm/i915/i915_reg.h         |  3 +++
 drivers/gpu/drm/i915/intel_ringbuffer.c | 18 ++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 104bd18..660afe1 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1653,11 +1653,18 @@ struct i915_wa_reg {
 	u32 mask;
-#define I915_MAX_WA_REGS 16
+ * RING_MAX_NONPRIV_SLOTS is per-engine but at this point we are only
+ * allowing it for RCS as we don't foresee any requirement of having
+ * a whitelist for other engines. When it is really required for
+ * other engines then the limit need to be increased.
+ */
 struct i915_workarounds {
 	struct i915_wa_reg reg[I915_MAX_WA_REGS];
 	u32 count;
+	u32 hw_whitelist_index[I915_NUM_RINGS];
 struct i915_virtual_gpu {
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 0a98889..6668bb0 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1635,6 +1635,9 @@ enum skl_disp_power_wells {
 #define   RING_WAIT		(1<<11) /* gen3+, PRBx_CTL */
 #define   RING_WAIT_SEMAPHORE	(1<<10) /* gen6+ */
+#define RING_FORCE_TO_NONPRIV(base) ((base)+0x4D0)
 #define GEN7_TLB_RD_ADDR	_MMIO(0x4700)
 #if 0
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 4060acf..354da81 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -787,6 +787,23 @@ static int wa_add(struct drm_i915_private *dev_priv,
 #define WA_WRITE(addr, val) WA_REG(addr, 0xffffffff, val)
+static inline int wa_ring_whitelist_reg(struct intel_engine_cs *ring,
+					i915_reg_t reg_addr)
+	struct drm_i915_private *dev_priv = ring->dev->dev_private;
+	struct i915_workarounds *wa = &dev_priv->workarounds;
+	const uint32_t index = wa->hw_whitelist_index[ring->id];
+		return -EINVAL;
+	WA_WRITE(_MMIO(RING_FORCE_TO_NONPRIV(ring->mmio_base) + index * 4),
+		 reg_addr.reg);
+	wa->hw_whitelist_index[ring->id]++;
+	return 0;
 static int gen8_init_workarounds(struct intel_engine_cs *ring)
 	struct drm_device *dev = ring->dev;
@@ -1115,6 +1132,7 @@ int init_workarounds_ring(struct intel_engine_cs *ring)
 	WARN_ON(ring->id != RCS);
 	dev_priv->workarounds.count = 0;
+	dev_priv->workarounds.hw_whitelist_index[ring->id] = 0;
 	if (IS_BROADWELL(dev))
 		return bdw_init_workarounds(ring);

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