[RFC v2 2/2] drm/i915/gmbus: Enable burst read

[Ramalingam C <ramalingam.c@intel.com>]

Support for Burst read in HW is added for HDCP2.2 compliance
requirement.

This patch enables the burst read for all the gmbus read of more than
511Bytes, on capable platforms.

v2:
  Extra line is removed.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h  |  1 +
 drivers/gpu/drm/i915/intel_i2c.c | 38 ++++++++++++++++++++++++++++++++++----
 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 4f583da0cee9..0ef162ee9ce0 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2984,6 +2984,7 @@ enum i915_power_well_id {
 #define   GMBUS_RATE_400KHZ	(2<<8) /* reserved on Pineview */
 #define   GMBUS_RATE_1MHZ	(3<<8) /* reserved on Pineview */
 #define   GMBUS_HOLD_EXT	(1<<7) /* 300ns hold time, rsvd on Pineview */
+#define   GMBUS_BYTE_CNT_OVERRIDE (1<<6)
 #define   GMBUS_PIN_DISABLED	0
 #define   GMBUS_PIN_SSC		1
 #define   GMBUS_PIN_VGADDC	2
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 7e92c7934657..2ee9cf2effcd 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -364,12 +364,24 @@ gmbus_wait_idle(struct drm_i915_private *dev_priv)
 static int
 gmbus_xfer_read_chunk(struct drm_i915_private *dev_priv,
 		      unsigned short addr, u8 *buf, unsigned int len,
-		      u32 gmbus1_index)
+		      u32 gmbus1_index, bool burst_read)
 {
+	unsigned int bytes_af_override, size;
+
+	if (burst_read) {
+		bytes_af_override = len - (((len / 256) - 1) * 256);
+		size = bytes_af_override;
+
+		I915_WRITE_FW(GMBUS0, (I915_READ_FW(GMBUS0) |
+			      GMBUS_BYTE_CNT_OVERRIDE));
+	} else {
+		size = len;
+	}
+
 	I915_WRITE_FW(GMBUS1,
 		      gmbus1_index |
 		      GMBUS_CYCLE_WAIT |
-		      (len << GMBUS_BYTE_COUNT_SHIFT) |
+		      (size << GMBUS_BYTE_COUNT_SHIFT) |
 		      (addr << GMBUS_SLAVE_ADDR_SHIFT) |
 		      GMBUS_SLAVE_READ | GMBUS_SW_RDY);
 	while (len) {
@@ -385,11 +397,23 @@ gmbus_xfer_read_chunk(struct drm_i915_private *dev_priv,
 			*buf++ = val & 0xff;
 			val >>= 8;
 		} while (--len && ++loop < 4);
+
+		if (burst_read && len == (bytes_af_override - 4))
+			I915_WRITE_FW(GMBUS0, (I915_READ_FW(GMBUS0) &
+				      ~GMBUS_BYTE_CNT_OVERRIDE));
 	}
 
 	return 0;
 }
 
+static bool gmbus_burst_read_supported(struct drm_i915_private *dev_priv)
+{
+	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv) ||
+	    IS_KABYLAKE(dev_priv))
+		return true;
+	return false;
+}
+
 static int
 gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
 		u32 gmbus1_index)
@@ -398,15 +422,21 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
 	unsigned int rx_size = msg->len;
 	unsigned int len;
 	int ret;
+	bool burst_read = false;
+
+	if (rx_size > BXT_GMBUS_BYTE_COUNT_MAX)
+		burst_read = gmbus_burst_read_supported(dev_priv);
 
 	do {
-		if (INTEL_GEN(dev_priv) >= 9)
+		if (burst_read)
+			len = rx_size;
+		else if (INTEL_GEN(dev_priv) >= 9)
 			len = min(rx_size, BXT_GMBUS_BYTE_COUNT_MAX);
 		else
 			len = min(rx_size, GMBUS_BYTE_COUNT_MAX);
 
 		ret = gmbus_xfer_read_chunk(dev_priv, msg->addr,
-					    buf, len, gmbus1_index);
+					    buf, len, gmbus1_index, burst_read);
 		if (ret)
 			return ret;
 
-- 
2.7.4

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