drm/i915: cope with large i2c transfers

The hardware, according to the specs, is limited to 256 byte transfers,
and current driver has no protections in case users attempt to do larger
transfers. The code will just stomp over status register and mayhem
ensues.

Let's split larger transfers into digestable chunks. Doing this allows
Atmel MXT driver on Pixel 1 function properly (it hasn't since commit
9d8dc3e529a19e427fd379118acd132520935c5d "Input: atmel_mxt_ts -
implement T44 message handling" which tries to consume multiple
touchscreen/touchpad reports in a single transaction).

Cc: stable@vger.kernel.org
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 56 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index b31088a..56e437e 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -270,18 +270,17 @@ gmbus_wait_idle(struct drm_i915_private *dev_priv)
 }
 
 static int
-gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
-		u32 gmbus1_index)
+gmbus_xfer_read_chunk(struct drm_i915_private *dev_priv,
+		      unsigned short addr, u8 *buf, unsigned int len,
+		      u32 gmbus1_index)
 {
 	int reg_offset = dev_priv->gpio_mmio_base;
-	u16 len = msg->len;
-	u8 *buf = msg->buf;
 
 	I915_WRITE(GMBUS1 + reg_offset,
 		   gmbus1_index |
 		   GMBUS_CYCLE_WAIT |
 		   (len << GMBUS_BYTE_COUNT_SHIFT) |
-		   (msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
+		   (addr << GMBUS_SLAVE_ADDR_SHIFT) |
 		   GMBUS_SLAVE_READ | GMBUS_SW_RDY);
 	while (len) {
 		int ret;
@@ -303,11 +302,35 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
 }
 
 static int
-gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
+gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
+		u32 gmbus1_index)
 {
-	int reg_offset = dev_priv->gpio_mmio_base;
-	u16 len = msg->len;
 	u8 *buf = msg->buf;
+	unsigned int rx_size = msg->len;
+	unsigned int len;
+	int ret;
+
+	do {
+		len = min(rx_size, GMBUS_BYTE_COUNT_MAX);
+
+		ret = gmbus_xfer_read_chunk(dev_priv, msg->addr,
+					    buf, len, gmbus1_index);
+		if (ret)
+			return ret;
+
+		rx_size -= len;
+		buf += len;
+	} while (rx_size != 0);
+
+	return 0;
+}
+
+static int
+gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
+		       unsigned short addr, u8 *buf, unsigned int len)
+{
+	int reg_offset = dev_priv->gpio_mmio_base;
+	unsigned int chunk_size = len;
 	u32 val, loop;
 
 	val = loop = 0;
@@ -319,8 +342,8 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
 	I915_WRITE(GMBUS3 + reg_offset, val);
 	I915_WRITE(GMBUS1 + reg_offset,
 		   GMBUS_CYCLE_WAIT |
-		   (msg->len << GMBUS_BYTE_COUNT_SHIFT) |
-		   (msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
+		   (chunk_size << GMBUS_BYTE_COUNT_SHIFT) |
+		   (addr << GMBUS_SLAVE_ADDR_SHIFT) |
 		   GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
 	while (len) {
 		int ret;
@@ -337,6 +360,29 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
 		if (ret)
 			return ret;
 	}
+
+	return 0;
+}
+
+static int
+gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
+{
+	u8 *buf = msg->buf;
+	unsigned int tx_size = msg->len;
+	unsigned int len;
+	int ret;
+
+	do {
+		len = min(tx_size, GMBUS_BYTE_COUNT_MAX);
+
+		ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len);
+		if (ret)
+			return ret;
+
+		buf += len;
+		tx_size -= len;
+	} while (tx_size != 0);
+
 	return 0;
 }