From: Kim Phillips Subject: Re: [PATCH v1] crypto: driver for tegra AES hardware Date: Wed, 16 Nov 2011 03:17:03 -0600 Message-ID: <20111116031703.e006c81ebf5368365e7a22fb@freescale.com> References: <1320489734-9085-1-git-send-email-vwadekar@nvidia.com> <20111105181025.69918e625a169ccb30d9b7c8@freescale.com> <4EBE48E8.60205@nvidia.com> <74CDBE0F657A3D45AFBB94109FB122FF1740805AB5@HQMAIL01.nvidia.com> <4EC1E642.2090309@nvidia.com> <74CDBE0F657A3D45AFBB94109FB122FF1740805D40@HQMAIL01.nvidia.com> <4EC362EA.3020204@nvidia.com> <20111116025720.27e6b710e8b333612862bb2e@freescale.com> <4EC37CBC.4060806@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Cc: Stephen Warren , "herbert-F6s6mLieUQo7FNHlEwC/lvQIK84fMopw@public.gmane.org" , "davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org" , "linux-crypto-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" To: Varun Wadekar Return-path: In-Reply-To: <4EC37CBC.4060806-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-crypto.vger.kernel.org On Wed, 16 Nov 2011 14:35:00 +0530 Varun Wadekar wrote: > > > it's not - it saves writes. > > Are you ok with this solution? Either way I wan to start with a clear > key table before programming the hardware. the hardware doesn't care. > > why do you need to clear the entire key table if it will be > > overwritten anyway? > > If you set a > 128-bit key and then set a 128-bit key, the remaining > bits still remain in the key table. Similarly, if we use updated IV in > one operation and want to use the initial IV for the next, the updated > IV will still remain in the key table. The entire key table is copied to > the AES engine. Even though, we program the engine with the exact number > of bits to use for the key and whether to use the updated/initial IV, I > feel its better if the unused bits are zero instead of having garbage. you're losing free performance. Kim