doc: add GCM AAD limitation in qat guide

Add limitation that AAD buffer must be padded with zeroes
in GCM case.

Fixes: d4f44265a1d7 ("doc: add limitation of AAD size to QAT guide")
Cc: stable@dpdk.org
Signed-off-by: Fiona Trahe <fiona.trahe@intel.com>
Acked-by: Arek Kusztal <arkadiuszx.kusztal@intel.com>

diff --git a/doc/guides/cryptodevs/qat.rst b/doc/guides/cryptodevs/qat.rst
index 9fb9f01..3ca70bc 100644 (file)
--- a/doc/guides/cryptodevs/qat.rst
+++ b/doc/guides/cryptodevs/qat.rst
@@ -79,10 +79,9 @@ Limitations
 * SNOW 3G (UIA2) and ZUC (EIA3) supported only if hash length and offset fields are byte-multiple.
 * No BSD support as BSD QAT kernel driver not available.
 * ZUC EEA3/EIA3 is not supported by dh895xcc devices
-* Maximum additional authenticated data (AAD) for GCM is 240 bytes long.
+* Maximum additional authenticated data (AAD) for GCM is 240 bytes long and must be passed to the device in a buffer rounded up to the nearest block-size multiple (x16) and padded with zeros.
 * Queue pairs are not thread-safe (that is, within a single queue pair, RX and TX from different lcores is not supported).
 
-
 Extra notes on KASUMI F9
 ~~~~~~~~~~~~~~~~~~~~~~~~