drm/radeon: fix atom aux payload size check for writes (v2)

The atom aux param interface only supports 4 bits for
the total write transfer size (header + payload).  This
limits us to 12 bytes of payload rather than 16.  Add a
check for this. Reads are not affected.

v2: switch to WARN_ON_ONCE

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
index 5bf825dfaa098ec6b6ad8f479856ce676f51ba21..8d74de82456e880cb01d7e8132cf6c1caf5fa864 100644 (file)
--- a/drivers/gpu/drm/radeon/atombios_dp.c
+++ b/drivers/gpu/drm/radeon/atombios_dp.c
@@ -178,6 +178,13 @@ radeon_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:
+               /* The atom implementation only supports writes with a max payload of
+                * 12 bytes since it uses 4 bits for the total count (header + payload)
+                * in the parameter space.  The atom interface supports 16 byte
+                * payloads for reads. The hw itself supports up to 16 bytes of payload.
+                */
+               if (WARN_ON_ONCE(msg->size > 12))
+                       return -E2BIG;
                /* tx_size needs to be 4 even for bare address packets since the atom
                 * table needs the info in tx_buf[3].
                 */