Introduction:
=============
Storage encryption has been one of the most required feature from security
point of view. QTI based storage encryption solution uses general purpose
crypto engine. While this kind of solution provide a decent amount of
performance, it falls short as storage speed is improving significantly
continuously. To overcome performance degradation, newer chips are going to
have Inline Crypto Engine (ICE) embedded into storage device. ICE is supposed
to meet the line speed of storage devices.

Hardware Description
====================
ICE is a HW block that is embedded into storage device such as UFS/eMMC. By
default, ICE works in bypass mode i.e. ICE HW does not perform any crypto
operation on data to be processed by storage device. If required, ICE can be
configured to perform crypto operation in one direction (i.e. either encryption
or decryption) or in both direction(both encryption & decryption).

When a switch between the operation modes(plain to crypto or crypto to plain)
is desired for a particular partition, SW must complete all transactions for
that particular partition before switching the crypto mode i.e. no crypto, one
direction crypto or both direction crypto operation. Requests for other
partitions are not impacted due to crypto mode switch.

ICE HW currently supports AES128/256 bit ECB & XTS mode encryption algorithms.

Keys for crypto operations are loaded from SW. Keys are stored in a lookup
table(LUT) located inside ICE HW. Maximum of 32 keys can be loaded in ICE key
LUT. A Key inside the LUT can be referred using a key index.

SW Description
==============
ICE HW has catagorized ICE registers in 2 groups: those which can be accessed by
only secure side i.e. TZ and those which can be accessed by non-secure side such
as HLOS as well. This requires that ICE driver to be split in two pieces: one
running from TZ space and another from HLOS space.

ICE driver from TZ would configure keys as requested by HLOS side.

ICE driver on HLOS side is responsible for initialization of ICE HW.

SW Architecture Diagram
=======================
Following are all the components involved in the ICE driver for control path:

+++++++++++++++++++++++++++++++++++++++++
+               App layer               +
+++++++++++++++++++++++++++++++++++++++++
+             System layer              +
+   ++++++++         +++++++            +
+   + VOLD +         + PFM +            +
+   ++++++++         +++++++            +
+         ||         ||                 +
+         ||         ||                 +
+         \/         \/                 +
+        ++++++++++++++                 +
+        + LibQSEECom +                 +
+        ++++++++++++++                 +
+++++++++++++++++++++++++++++++++++++++++
+             Kernel                    +       +++++++++++++++++
+                                       +       +     KMS       +
+  +++++++  +++++++++++  +++++++++++    +       +++++++++++++++++
+  + ICE +  + Storage +  + QSEECom +    +       +   ICE Driver  +
+++++++++++++++++++++++++++++++++++++++++ <===> +++++++++++++++++
               ||                                    ||
               ||                                    ||
               \/                                    \/
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+                      Storage Device                           +
+                      ++++++++++++++                           +
+                      +   ICE HW   +                           +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Use Cases:
----------
a) Device bootup
ICE HW is detected during bootup time and corresponding probe function is
called. ICE driver parses its data from device tree node. ICE HW and storage
HW are tightly coupled. Storage device probing is dependent upon ICE device
probing. ICE driver configures all the required registers to put the ICE HW
in bypass mode.

b) Configuring keys
Currently, there are couple of use cases to configure the keys.

1) Full Disk Encryption(FDE)
System layer(VOLD) at invocation of apps layer would call libqseecom to create
the encryption key. Libqseecom calls qseecom driver to communicate with KMS
module on the secure side i.e. TZ. KMS would call ICE driver on the TZ side to
create and set the keys in ICE HW. At the end of transaction, VOLD would have
key index of key LUT where encryption key is present.

2) Per File Encryption (PFE)
Per File Manager(PFM) calls QSEECom api to create the key. PFM has a peer comp-
onent(PFT) at kernel layer which gets the corresponding key index from PFM.

Following are all the components involved in the ICE driver for data path:

+++++++++++++++++++++++++++++++++++++++++
+               App layer               +
+++++++++++++++++++++++++++++++++++++++++
+              VFS                      +
+---------------------------------------+
+         File System (EXT4)            +
+---------------------------------------+
+             Block Layer               +
+ --------------------------------------+
+                              +++++++  +
+              dm-req-crypt => + PFT +  +
+                              +++++++  +
+                                       +
+---------------------------------------+
+    +++++++++++           +++++++      +
+    + Storage +           + ICE +      +
+++++++++++++++++++++++++++++++++++++++++
+                  ||                   +
+                  || (Storage Req with +
+                  \/  ICE parameters ) +
+++++++++++++++++++++++++++++++++++++++++
+          Storage Device               +
+          ++++++++++++++               +
+          +   ICE HW   +               +
+++++++++++++++++++++++++++++++++++++++++

c) Data transaction
Once the crypto key has been configured, VOLD/PFM creates device mapping for
data partition. As part of device mapping VOLD passes key index, crypto
algorithm, mode and key length to dm layer. In case of PFE, keys are provided
by PFT as and when request is processed by dm-req-crypt. When any application
needs to read/write data, it would go through DM layer which would add crypto
information, provided by VOLD/PFT, to Request. For each Request, Storage driver
would ask ICE driver to configure crypto part of request. ICE driver extracts
crypto data from Request structure and provide it to storage driver which would
finally dispatch request to storage device.

d) Error Handling
Due to issue # 1 mentioned in "Known Issues", ICE driver does not register for
any interrupt. However, it enables sources of interrupt for ICE HW. After each
data transaction, Storage driver receives transaction completion event. As part
of event handling, storage driver calls  ICE driver to check if any of ICE
interrupt status is set. If yes, storage driver returns error to upper layer.

Error handling would be changed in future chips.

Interfaces
==========
ICE driver exposes interfaces for storage driver to :
1. Get the global instance of ICE driver
2. Get the implemented interfaces of the particular ice instance
3. Initialize the ICE HW
4. Reset the ICE HW
5. Resume/Suspend the ICE HW
6. Get the Crypto configuration for the data request for storage
7. Check if current data transaction has generated any interrupt

Driver Parameters
=================
This driver is built and statically linked into the kernel; therefore,
there are no module parameters supported by this driver.

There are no kernel command line parameters supported by this driver.

Power Management
================
ICE driver does not do power management on its own as it is part of storage
hardware. Whenever storage driver receives request for power collapse/suspend
resume, it would call ICE driver which exposes APIs for Storage HW. ICE HW
during power collapse or reset, wipes crypto configuration data. When ICE
driver receives request to resume, it would ask ICE driver on TZ side to
restore the configuration. ICE driver does not do anything as part of power
collapse or suspend event.

Interface:
==========
ICE driver exposes following APIs for storage driver to use:

int (*init)(struct platform_device *, void *, ice_success_cb, ice_error_cb);
	-- This function is invoked by storage controller during initialization of
	storage controller. Storage controller would provide success and error call
	backs which would be invoked asynchronously once ICE HW init is done.

int (*reset)(struct platform_device *);
	-- ICE HW reset as part of storage controller reset. When storage controller
	received reset command, it would call reset on ICE HW. As of now, ICE HW
	does not need to do anything as part of reset.

int (*resume)(struct platform_device *);
	-- ICE HW while going to reset, wipes all crypto keys and other data from ICE
	HW. ICE driver would reconfigure those data as part of resume operation.

int (*suspend)(struct platform_device *);
	-- This API would be called by storage driver when storage device is going to
	suspend mode. As of today, ICE driver does not do anything to handle suspend.

int (*config)(struct platform_device *, struct request* , struct ice_data_setting*);
	-- Storage driver would call this interface to get all crypto data required to
	perform crypto operation.

int (*status)(struct platform_device *);
	-- Storage driver would call this interface to check if previous data transfer
	generated any error.

Config options
==============
This driver is enabled by the kernel config option CONFIG_CRYPTO_DEV_MSM_ICE.

Dependencies
============
ICE driver depends upon corresponding ICE driver on TZ side to function
appropriately.

Known Issues
============
1. ICE HW emits 0s even if it has generated an interrupt
This issue has significant impact on how ICE interrupts are handled. Currently,
ICE driver does not register for any of the ICE interrupts but enables the
sources of interrupt. Once storage driver asks to check the status of interrupt,
it reads and clears the clear status and provide read status to storage driver.
This mechanism though not optimal but prevents filesystem curruption.
This issue has been fixed in newer chips.

2. ICE HW wipes all crypto data during power collapse
This issue necessiate that ICE driver on TZ side store the crypto material
which is not required in the case of general purpose crypto engine.
This issue has been fixed in newer chips.

Further Improvements
====================
Currently, Due to PFE use case, ICE driver is dependent upon dm-req-crypt to
provide the keys as part of request structure. This couples ICE driver with
dm-req-crypt based solution. It is under discussion to expose an IOCTL based
and registeration based interface APIs from ICE driver. ICE driver would use
these two interfaces to find out if any key exists for current request. If
yes, choose the right key index received from IOCTL or registeration based
APIs. If not, dont set any crypto parameter in the request.