drm/i915: support address only i2c-over-aux transactions

To support bare address requests used by the drm dp helpers.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index a0dad1a2f819..d2a55884ad52 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -575,7 +575,8 @@ out:
         return ret;
 }
 
-#define HEADER_SIZE     4
+#define BARE_ADDRESS_SIZE       3
+#define HEADER_SIZE             (BARE_ADDRESS_SIZE + 1)
 static ssize_t
 intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 {
@@ -592,7 +593,7 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
         switch (msg->request & ~DP_AUX_I2C_MOT) {
         case DP_AUX_NATIVE_WRITE:
         case DP_AUX_I2C_WRITE:
-                txsize = HEADER_SIZE + msg->size;
+                txsize = msg->size ? HEADER_SIZE + msg->size : BARE_ADDRESS_SIZE;
                 rxsize = 1;
 
                 if (WARN_ON(txsize > 20))
@@ -611,7 +612,7 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 
         case DP_AUX_NATIVE_READ:
         case DP_AUX_I2C_READ:
-                txsize = HEADER_SIZE;
+                txsize = msg->size ? HEADER_SIZE : BARE_ADDRESS_SIZE;
                 rxsize = msg->size + 1;
 
                 if (WARN_ON(rxsize > 20))