mirror of
https://github.com/AetherDroid/android_kernel_samsung_on5xelte.git
synced 2025-09-05 16:07:46 -04:00
Fixed MTP to work with TWRP
This commit is contained in:
awab228
commit
f6dfaef42e
50820 changed files with 20846062 additions and 0 deletions
148
Documentation/i2c/functionality
Normal file
148
Documentation/i2c/functionality
Normal file
|
|
@ -0,0 +1,148 @@
|
|||
INTRODUCTION
|
||||
------------
|
||||
|
||||
Because not every I2C or SMBus adapter implements everything in the
|
||||
I2C specifications, a client can not trust that everything it needs
|
||||
is implemented when it is given the option to attach to an adapter:
|
||||
the client needs some way to check whether an adapter has the needed
|
||||
functionality.
|
||||
|
||||
|
||||
FUNCTIONALITY CONSTANTS
|
||||
-----------------------
|
||||
|
||||
For the most up-to-date list of functionality constants, please check
|
||||
<linux/i2c.h>!
|
||||
|
||||
I2C_FUNC_I2C Plain i2c-level commands (Pure SMBus
|
||||
adapters typically can not do these)
|
||||
I2C_FUNC_10BIT_ADDR Handles the 10-bit address extensions
|
||||
I2C_FUNC_PROTOCOL_MANGLING Knows about the I2C_M_IGNORE_NAK,
|
||||
I2C_M_REV_DIR_ADDR and I2C_M_NO_RD_ACK
|
||||
flags (which modify the I2C protocol!)
|
||||
I2C_FUNC_NOSTART Can skip repeated start sequence
|
||||
I2C_FUNC_SMBUS_QUICK Handles the SMBus write_quick command
|
||||
I2C_FUNC_SMBUS_READ_BYTE Handles the SMBus read_byte command
|
||||
I2C_FUNC_SMBUS_WRITE_BYTE Handles the SMBus write_byte command
|
||||
I2C_FUNC_SMBUS_READ_BYTE_DATA Handles the SMBus read_byte_data command
|
||||
I2C_FUNC_SMBUS_WRITE_BYTE_DATA Handles the SMBus write_byte_data command
|
||||
I2C_FUNC_SMBUS_READ_WORD_DATA Handles the SMBus read_word_data command
|
||||
I2C_FUNC_SMBUS_WRITE_WORD_DATA Handles the SMBus write_byte_data command
|
||||
I2C_FUNC_SMBUS_PROC_CALL Handles the SMBus process_call command
|
||||
I2C_FUNC_SMBUS_READ_BLOCK_DATA Handles the SMBus read_block_data command
|
||||
I2C_FUNC_SMBUS_WRITE_BLOCK_DATA Handles the SMBus write_block_data command
|
||||
I2C_FUNC_SMBUS_READ_I2C_BLOCK Handles the SMBus read_i2c_block_data command
|
||||
I2C_FUNC_SMBUS_WRITE_I2C_BLOCK Handles the SMBus write_i2c_block_data command
|
||||
|
||||
A few combinations of the above flags are also defined for your convenience:
|
||||
|
||||
I2C_FUNC_SMBUS_BYTE Handles the SMBus read_byte
|
||||
and write_byte commands
|
||||
I2C_FUNC_SMBUS_BYTE_DATA Handles the SMBus read_byte_data
|
||||
and write_byte_data commands
|
||||
I2C_FUNC_SMBUS_WORD_DATA Handles the SMBus read_word_data
|
||||
and write_word_data commands
|
||||
I2C_FUNC_SMBUS_BLOCK_DATA Handles the SMBus read_block_data
|
||||
and write_block_data commands
|
||||
I2C_FUNC_SMBUS_I2C_BLOCK Handles the SMBus read_i2c_block_data
|
||||
and write_i2c_block_data commands
|
||||
I2C_FUNC_SMBUS_EMUL Handles all SMBus commands that can be
|
||||
emulated by a real I2C adapter (using
|
||||
the transparent emulation layer)
|
||||
|
||||
In kernel versions prior to 3.5 I2C_FUNC_NOSTART was implemented as
|
||||
part of I2C_FUNC_PROTOCOL_MANGLING.
|
||||
|
||||
|
||||
ADAPTER IMPLEMENTATION
|
||||
----------------------
|
||||
|
||||
When you write a new adapter driver, you will have to implement a
|
||||
function callback `functionality'. Typical implementations are given
|
||||
below.
|
||||
|
||||
A typical SMBus-only adapter would list all the SMBus transactions it
|
||||
supports. This example comes from the i2c-piix4 driver:
|
||||
|
||||
static u32 piix4_func(struct i2c_adapter *adapter)
|
||||
{
|
||||
return I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE |
|
||||
I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA |
|
||||
I2C_FUNC_SMBUS_BLOCK_DATA;
|
||||
}
|
||||
|
||||
A typical full-I2C adapter would use the following (from the i2c-pxa
|
||||
driver):
|
||||
|
||||
static u32 i2c_pxa_functionality(struct i2c_adapter *adap)
|
||||
{
|
||||
return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
|
||||
}
|
||||
|
||||
I2C_FUNC_SMBUS_EMUL includes all the SMBus transactions (with the
|
||||
addition of I2C block transactions) which i2c-core can emulate using
|
||||
I2C_FUNC_I2C without any help from the adapter driver. The idea is
|
||||
to let the client drivers check for the support of SMBus functions
|
||||
without having to care whether the said functions are implemented in
|
||||
hardware by the adapter, or emulated in software by i2c-core on top
|
||||
of an I2C adapter.
|
||||
|
||||
|
||||
CLIENT CHECKING
|
||||
---------------
|
||||
|
||||
Before a client tries to attach to an adapter, or even do tests to check
|
||||
whether one of the devices it supports is present on an adapter, it should
|
||||
check whether the needed functionality is present. The typical way to do
|
||||
this is (from the lm75 driver):
|
||||
|
||||
static int lm75_detect(...)
|
||||
{
|
||||
(...)
|
||||
if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
|
||||
I2C_FUNC_SMBUS_WORD_DATA))
|
||||
goto exit;
|
||||
(...)
|
||||
}
|
||||
|
||||
Here, the lm75 driver checks if the adapter can do both SMBus byte data
|
||||
and SMBus word data transactions. If not, then the driver won't work on
|
||||
this adapter and there's no point in going on. If the check above is
|
||||
successful, then the driver knows that it can call the following
|
||||
functions: i2c_smbus_read_byte_data(), i2c_smbus_write_byte_data(),
|
||||
i2c_smbus_read_word_data() and i2c_smbus_write_word_data(). As a rule of
|
||||
thumb, the functionality constants you test for with
|
||||
i2c_check_functionality() should match exactly the i2c_smbus_* functions
|
||||
which you driver is calling.
|
||||
|
||||
Note that the check above doesn't tell whether the functionalities are
|
||||
implemented in hardware by the underlying adapter or emulated in
|
||||
software by i2c-core. Client drivers don't have to care about this, as
|
||||
i2c-core will transparently implement SMBus transactions on top of I2C
|
||||
adapters.
|
||||
|
||||
|
||||
CHECKING THROUGH /DEV
|
||||
---------------------
|
||||
|
||||
If you try to access an adapter from a userspace program, you will have
|
||||
to use the /dev interface. You will still have to check whether the
|
||||
functionality you need is supported, of course. This is done using
|
||||
the I2C_FUNCS ioctl. An example, adapted from the i2cdetect program, is
|
||||
below:
|
||||
|
||||
int file;
|
||||
if (file = open("/dev/i2c-0", O_RDWR) < 0) {
|
||||
/* Some kind of error handling */
|
||||
exit(1);
|
||||
}
|
||||
if (ioctl(file, I2C_FUNCS, &funcs) < 0) {
|
||||
/* Some kind of error handling */
|
||||
exit(1);
|
||||
}
|
||||
if (!(funcs & I2C_FUNC_SMBUS_QUICK)) {
|
||||
/* Oops, the needed functionality (SMBus write_quick function) is
|
||||
not available! */
|
||||
exit(1);
|
||||
}
|
||||
/* Now it is safe to use the SMBus write_quick command */
|
||||
Loading…
Add table
Add a link
Reference in a new issue