kernel_samsung_msm8974/Documentation/crypto/msm/qcrypto.txt

Introduction:
=============

Qualcomm Crypto (qcrypto) driver is a Linux crypto driver which interfaces
with the Linux kernel crypto API layer to provide the HW crypto functions.
This driver is accessed by kernel space apps via the kernel crypto API layer.
At present there is no means for user space apps to access this module.

Hardware description:
=====================

Qualcomm Crypto HW device family provides a series of algorithms implemented
in the device.

Crypto 2 hardware provides hashing - SHA-1, SHA-256, ciphering - DES, 3DES, AES
algorithms, and concurrent operations of hashing, and ciphering.

In addition to those functions provided by Crypto 2 HW, Crypto 3 provides fast
AES algorithms.

In addition to those functions provided by Crypto 3 HW, Crypto 3E provides
HMAC-SHA1 hashing algorithm.

In addition to those functions provided by Crypto 3 HW, Crypto 4.0 provides
HMAC-SHA1/SHA256, AES CBC-MAC hashing algorithm and AES XTS/CCM cipher
algorithms.


Software description
====================

The module init function (_qcrypto_init()), does a platform_register(),
to register the driver. As the result, the driver probe function,
_qcrypto_probe(), will be invoked for each registered device.

In the probe function, driver opens the low level CE (qce_open), and
registers the supported algorithms to the kernel crypto API layer.
Currently, qcrypto supports the following algorithms.

      ablkcipher -
          cbc(aes),ecb(aes),ctr(aes)
      ahash -
          sha1, sha256
      aead -
          authenc(hmac(sha1),cbc(aes))

      The hmac(sha1), hmac(sha256, authenc(hmac(sha1),cbc(aes)), ccm(aes)
      and xts(aes) algorithms are registered for some platforms that
      support these in the CE hardware

The HW device  can support various algorithms. However, the most important
algorithms to gain the performance using a HW crypto accelerator are
AEAD, and ABLKCIPHER.

AEAD stands for "authentication encryption with association data".
ABLKCIPHER stands of "asynchronous block cipher".

The AEAD structure is described in the following header file
    LINUX/opensource/kernel/include/crypto/aead.h

The design of the driver is to allow multiple requests
issued from kernel client SW (eg IPSec).
Therefore, the driver will have to internally queue the requests, and
serialize the requests to the low level qce driver.

When a request is received from the client, if there is no outstanding
request, a qce (or qce40) request is issued, otherwise, the request is
queued in the driver queue.

On completion of a request, the qce (or qce40) invokes the registered
callback from the qcrypto.  The internal tasklet (done_tasklet) is scheduled
in this callback function. The sole purpose of done_tasklet is
to call the completion of the current active request, and
issue more requests to the qce (or qce40), if any exists.

A spin lock is used to protect the critical section of internal queue to
be accessed from multiple tasks, SMP, and completion callback
from qce.

The driver maintains a set of statistics using debug fs. The files are
in /debug/qcrypto/stats1, /debug/qcrypto/stats2, /debug/qcrypto/stats3;
one for each instance of device. Reading the file associated with
a device will retrieve the driver statistics for that device.
Any write to the file will clear the statistics.

Test vectors for  authenc(hmac(sha1),cbc(aes)) algorithm are
developed offline, and imported to crypto/testmgr.c, and crypto/testmgr.h.


Power Management
================
  none


Interface:
==========
The kernel interface is defined in
    LINUX/opensource/kernel/include/linux/crypto.h.


Module parameters:
==================

All the platform specific parameters are defined in the board init
file, eg. arch/arm/mach-msm/board-mssm7x30.c for msm7x30.

Dependencies:
=============
qce driver.


User space utilities:
=====================
  n/a

Known issues:
=============
  n/a

To do:
======
  Add Hashing algorithms.


Limitations:
===============
(1) Each packet transfer size (for cipher and hash) is limited to maximum of
    32KB.  This is a limitation in the crypto engine hardware. Client will
    have to break packets larger than 32KB into multiple requests of smaller
    size data packets.

(2) Do not load this driver if your device has user space apps that needs to
    access the crypto hardware. Please make sure to have the qcrypto module
    disabled/unloaded.
    Not having the driver loaded, will result in the kernel space apps to use
    the registered software implementation of the crypto algorithms.

(3) If your device has Playready application enabled and uses the qcedev module
    to access the crypto hardware accelarator, please be informed that for
    performance reasons, the CE hardware will need to be dedicated to playready
    application.  Any other user space or kernel application should be implemented
    to use the software implemenation of the crypto algorithms.

    (NOTE:  Please refer to details on the limitations listed in qce/40.txt)