adulau/aha
1
0
Fork 0
mirror of https://github.com/adulau/aha.git synced 2025-01-03 22:53:18 +00:00
Code Issues Projects Releases Packages Wiki Activity
aha/drivers/i2c/algos/i2c-algo-bit.c
Jean Delvare 424ed67c7d i2c-algo-bit: Implement a 50/50 SCL duty cycle 
The original i2c-algo-bit implementation uses a 33/66 SCL duty cycle
when bits are being written on the bus. While the I2C specification
doesn't forbid it, this prevents us from driving the I2C bus to its
max speed, limiting us to 66 kbps max on standard I2C busses.

Implementing a 50/50 duty cycle instead lets us max out the bandwidth
up to the theoretical max of 100 kbps on standard I2C busses. This is
particularly important when large amounts of data need to be transfered
over the bus, as is the case with some TV adapters when the firmware is
being uploaded.

In fact this change even allows, at least in theory, fast-mode I2C
support at 125, 166 and 250 kbps. There's no way to reach the
theoretical max of 400 kbps with this implementation. But I don't
think we want to put efforts in that direction anyway: software-driven
I2C is very CPU-intensive and bad for latency.

Other timing changes:
* Don't set SDA high explicitly on error, we're going to issue a stop
  condition before we leave anyway.
* If an error occurs when sending the slave address, yield the CPU
  before retrying, and remove the additional delay after the new start
  condition.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
2007-05-01 23:26:33 +02:00

599 lines
16 KiB
C
Raw Blame History

/* ------------------------------------------------------------------------- */
/* i2c-algo-bit.c i2c driver algorithms for bit-shift adapters */
/* ------------------------------------------------------------------------- */
/* Copyright (C) 1995-2000 Simon G. Vogl
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
/* ------------------------------------------------------------------------- */
/* With some changes from Frodo Looijaard <frodol@dds.nl>, Kyösti Mälkki
<kmalkki@cc.hut.fi> and Jean Delvare <khali@linux-fr.org> */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/i2c.h>
#include <linux/i2c-algo-bit.h>
/* ----- global defines ----------------------------------------------- */
#define DEB(x) if (i2c_debug>=1) x;
#define DEB2(x) if (i2c_debug>=2) x;
#define DEBSTAT(x) if (i2c_debug>=3) x; /* print several statistical values*/
#define DEBPROTO(x) if (i2c_debug>=9) { x; }
/* debug the protocol by showing transferred bits */
/* ----- global variables --------------------------------------------- */
/* module parameters:
*/
static int i2c_debug;
static int bit_test; /* see if the line-setting functions work */
/* --- setting states on the bus with the right timing: --------------- */
#define setsda(adap,val) adap->setsda(adap->data, val)
#define setscl(adap,val) adap->setscl(adap->data, val)
#define getsda(adap) adap->getsda(adap->data)
#define getscl(adap) adap->getscl(adap->data)
static inline void sdalo(struct i2c_algo_bit_data *adap)
{
setsda(adap,0);
udelay((adap->udelay + 1) / 2);
}
static inline void sdahi(struct i2c_algo_bit_data *adap)
{
setsda(adap,1);
udelay((adap->udelay + 1) / 2);
}
static inline void scllo(struct i2c_algo_bit_data *adap)
{
setscl(adap,0);
udelay(adap->udelay / 2);
}
/*
* Raise scl line, and do checking for delays. This is necessary for slower
* devices.
*/
static int sclhi(struct i2c_algo_bit_data *adap)
{
unsigned long start;
setscl(adap,1);
/* Not all adapters have scl sense line... */
if (!adap->getscl)
goto done;
start=jiffies;
while (! getscl(adap) ) {
/* the hw knows how to read the clock line,
* so we wait until it actually gets high.
* This is safer as some chips may hold it low
* while they are processing data internally.
*/
if (time_after_eq(jiffies, start+adap->timeout)) {
return -ETIMEDOUT;
}
cond_resched();
}
DEBSTAT(printk(KERN_DEBUG "needed %ld jiffies\n", jiffies-start));
done:
udelay(adap->udelay);
return 0;
}
/* --- other auxiliary functions -------------------------------------- */
static void i2c_start(struct i2c_algo_bit_data *adap)
{
/* assert: scl, sda are high */
DEBPROTO(printk("S "));
setsda(adap, 0);
udelay(adap->udelay);
scllo(adap);
}
static void i2c_repstart(struct i2c_algo_bit_data *adap)
{
/* assert: scl is low */
DEBPROTO(printk(" Sr "));
sdahi(adap);
sclhi(adap);
setsda(adap, 0);
udelay(adap->udelay);
scllo(adap);
}
static void i2c_stop(struct i2c_algo_bit_data *adap)
{
DEBPROTO(printk("P\n"));
/* assert: scl is low */
sdalo(adap);
sclhi(adap);
setsda(adap, 1);
udelay(adap->udelay);
}
/* send a byte without start cond., look for arbitration,
check ackn. from slave */
/* returns:
* 1 if the device acknowledged
* 0 if the device did not ack
* -ETIMEDOUT if an error occurred (while raising the scl line)
*/
static int i2c_outb(struct i2c_adapter *i2c_adap, char c)
{
int i;
int sb;
int ack;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
/* assert: scl is low */
for ( i=7 ; i>=0 ; i-- ) {
sb = c & ( 1 << i );
setsda(adap,sb);
udelay((adap->udelay + 1) / 2);
DEBPROTO(printk(KERN_DEBUG "%d",sb!=0));
if (sclhi(adap)<0) { /* timed out */
DEB2(printk(KERN_DEBUG " i2c_outb: 0x%02x, timeout at bit #%d\n", c&0xff, i));
return -ETIMEDOUT;
};
/* do arbitration here:
* if ( sb && ! getsda(adap) ) -> ouch! Get out of here.
*/
scllo(adap);
}
sdahi(adap);
if (sclhi(adap)<0){ /* timeout */
DEB2(printk(KERN_DEBUG " i2c_outb: 0x%02x, timeout at ack\n", c&0xff));
return -ETIMEDOUT;
};
/* read ack: SDA should be pulled down by slave */
ack=getsda(adap); /* ack: sda is pulled low ->success. */
DEB2(printk(KERN_DEBUG " i2c_outb: 0x%02x , getsda() = %d\n", c & 0xff, ack));
DEBPROTO( printk(KERN_DEBUG "[%2.2x]",c&0xff) );
DEBPROTO(if (0==ack){ printk(KERN_DEBUG " A ");} else printk(KERN_DEBUG " NA ") );
scllo(adap);
return 0==ack; /* return 1 if device acked */
/* assert: scl is low (sda undef) */
}
static int i2c_inb(struct i2c_adapter *i2c_adap)
{
/* read byte via i2c port, without start/stop sequence */
/* acknowledge is sent in i2c_read. */
int i;
unsigned char indata=0;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
/* assert: scl is low */
sdahi(adap);
for (i=0;i<8;i++) {
if (sclhi(adap)<0) { /* timeout */
DEB2(printk(KERN_DEBUG " i2c_inb: timeout at bit #%d\n", 7-i));
return -ETIMEDOUT;
};
indata *= 2;
if ( getsda(adap) )
indata |= 0x01;
setscl(adap, 0);
udelay(i == 7 ? adap->udelay / 2 : adap->udelay);
}
/* assert: scl is low */
DEB2(printk(KERN_DEBUG "i2c_inb: 0x%02x\n", indata & 0xff));
DEBPROTO(printk(KERN_DEBUG " 0x%02x", indata & 0xff));
return (int) (indata & 0xff);
}
/*
* Sanity check for the adapter hardware - check the reaction of
* the bus lines only if it seems to be idle.
*/
static int test_bus(struct i2c_algo_bit_data *adap, char* name) {
int scl,sda;
if (adap->getscl==NULL)
printk(KERN_INFO "i2c-algo-bit.o: Testing SDA only, "
"SCL is not readable.\n");
sda=getsda(adap);
scl=(adap->getscl==NULL?1:getscl(adap));
printk(KERN_DEBUG "i2c-algo-bit.o: (0) scl=%d, sda=%d\n",scl,sda);
if (!scl || !sda ) {
printk(KERN_WARNING "i2c-algo-bit.o: %s seems to be busy.\n", name);
goto bailout;
}
sdalo(adap);
sda=getsda(adap);
scl=(adap->getscl==NULL?1:getscl(adap));
printk(KERN_DEBUG "i2c-algo-bit.o: (1) scl=%d, sda=%d\n",scl,sda);
if ( 0 != sda ) {
printk(KERN_WARNING "i2c-algo-bit.o: SDA stuck high!\n");
goto bailout;
}
if ( 0 == scl ) {
printk(KERN_WARNING "i2c-algo-bit.o: SCL unexpected low "
"while pulling SDA low!\n");
goto bailout;
}
sdahi(adap);
sda=getsda(adap);
scl=(adap->getscl==NULL?1:getscl(adap));
printk(KERN_DEBUG "i2c-algo-bit.o: (2) scl=%d, sda=%d\n",scl,sda);
if ( 0 == sda ) {
printk(KERN_WARNING "i2c-algo-bit.o: SDA stuck low!\n");
goto bailout;
}
if ( 0 == scl ) {
printk(KERN_WARNING "i2c-algo-bit.o: SCL unexpected low "
"while pulling SDA high!\n");
goto bailout;
}
scllo(adap);
sda=getsda(adap);
scl=(adap->getscl==NULL?0:getscl(adap));
printk(KERN_DEBUG "i2c-algo-bit.o: (3) scl=%d, sda=%d\n",scl,sda);
if ( 0 != scl ) {
printk(KERN_WARNING "i2c-algo-bit.o: SCL stuck high!\n");
goto bailout;
}
if ( 0 == sda ) {
printk(KERN_WARNING "i2c-algo-bit.o: SDA unexpected low "
"while pulling SCL low!\n");
goto bailout;
}
sclhi(adap);
sda=getsda(adap);
scl=(adap->getscl==NULL?1:getscl(adap));
printk(KERN_DEBUG "i2c-algo-bit.o: (4) scl=%d, sda=%d\n",scl,sda);
if ( 0 == scl ) {
printk(KERN_WARNING "i2c-algo-bit.o: SCL stuck low!\n");
goto bailout;
}
if ( 0 == sda ) {
printk(KERN_WARNING "i2c-algo-bit.o: SDA unexpected low "
"while pulling SCL high!\n");
goto bailout;
}
printk(KERN_INFO "i2c-algo-bit.o: %s passed test.\n",name);
return 0;
bailout:
sdahi(adap);
sclhi(adap);
return -ENODEV;
}
/* ----- Utility functions
*/
/* try_address tries to contact a chip for a number of
* times before it gives up.
* return values:
* 1 chip answered
* 0 chip did not answer
* -x transmission error
*/
static int try_address(struct i2c_adapter *i2c_adap,
unsigned char addr, int retries)
{
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
int i,ret = -1;
for (i=0;i<=retries;i++) {
ret = i2c_outb(i2c_adap,addr);
if (ret == 1 || i == retries)
break;
i2c_stop(adap);
udelay(adap->udelay);
yield();
i2c_start(adap);
}
DEB2(if (i)
printk(KERN_DEBUG "i2c-algo-bit.o: Used %d tries to %s client at 0x%02x : %s\n",
i+1, addr & 1 ? "read" : "write", addr>>1,
ret==1 ? "success" : ret==0 ? "no ack" : "failed, timeout?" )
);
return ret;
}
static int sendbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
char c;
const char *temp = msg->buf;
int count = msg->len;
unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
int retval;
int wrcount=0;
while (count > 0) {
c = *temp;
DEB2(dev_dbg(&i2c_adap->dev, "sendbytes: writing %2.2X\n", c&0xff));
retval = i2c_outb(i2c_adap,c);
if ((retval>0) || (nak_ok && (retval==0))) { /* ok or ignored NAK */
count--;
temp++;
wrcount++;
} else { /* arbitration or no acknowledge */
dev_err(&i2c_adap->dev, "sendbytes: error - bailout.\n");
return (retval<0)? retval : -EFAULT;
/* got a better one ?? */
}
}
return wrcount;
}
static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
int inval;
int rdcount=0; /* counts bytes read */
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
char *temp = msg->buf;
int count = msg->len;
while (count > 0) {
inval = i2c_inb(i2c_adap);
if (inval>=0) {
*temp = inval;
rdcount++;
} else { /* read timed out */
printk(KERN_ERR "i2c-algo-bit.o: readbytes: i2c_inb timed out.\n");
break;
}
temp++;
count--;
if (msg->flags & I2C_M_NO_RD_ACK)
continue;
/* assert: sda is high */
if ( count > 0 ) { /* send ack */
setsda(adap, 0);
udelay((adap->udelay + 1) / 2);
DEBPROTO(printk(" Am "));
} else {
/* neg. ack on last byte */
udelay((adap->udelay + 1) / 2);
DEBPROTO(printk(" NAm "));
}
if (sclhi(adap)<0) { /* timeout */
printk(KERN_ERR "i2c-algo-bit.o: readbytes: Timeout at ack\n");
return -ETIMEDOUT;
};
scllo(adap);
/* Some SMBus transactions require that we receive the
transaction length as the first read byte. */
if (rdcount == 1 && (msg->flags & I2C_M_RECV_LEN)) {
if (inval <= 0 || inval > I2C_SMBUS_BLOCK_MAX) {
printk(KERN_ERR "i2c-algo-bit: readbytes: "
"invalid block length (%d)\n", inval);
return -EREMOTEIO;
}
/* The original count value accounts for the extra
bytes, that is, either 1 for a regular transaction,
or 2 for a PEC transaction. */
count += inval;
msg->len += inval;
}
}
return rdcount;
}
/* doAddress initiates the transfer by generating the start condition (in
* try_address) and transmits the address in the necessary format to handle
* reads, writes as well as 10bit-addresses.
* returns:
* 0 everything went okay, the chip ack'ed, or IGNORE_NAK flag was set
* -x an error occurred (like: -EREMOTEIO if the device did not answer, or
* -ETIMEDOUT, for example if the lines are stuck...)
*/
static int bit_doAddress(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
unsigned short flags = msg->flags;
unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
unsigned char addr;
int ret, retries;
retries = nak_ok ? 0 : i2c_adap->retries;
if ( (flags & I2C_M_TEN) ) {
/* a ten bit address */
addr = 0xf0 | (( msg->addr >> 7) & 0x03);
DEB2(printk(KERN_DEBUG "addr0: %d\n",addr));
/* try extended address code...*/
ret = try_address(i2c_adap, addr, retries);
if ((ret != 1) && !nak_ok) {
printk(KERN_ERR "died at extended address code.\n");
return -EREMOTEIO;
}
/* the remaining 8 bit address */
ret = i2c_outb(i2c_adap,msg->addr & 0x7f);
if ((ret != 1) && !nak_ok) {
/* the chip did not ack / xmission error occurred */
printk(KERN_ERR "died at 2nd address code.\n");
return -EREMOTEIO;
}
if ( flags & I2C_M_RD ) {
i2c_repstart(adap);
/* okay, now switch into reading mode */
addr |= 0x01;
ret = try_address(i2c_adap, addr, retries);
if ((ret!=1) && !nak_ok) {
printk(KERN_ERR "died at extended address code.\n");
return -EREMOTEIO;
}
}
} else { /* normal 7bit address */
addr = ( msg->addr << 1 );
if (flags & I2C_M_RD )
addr |= 1;
if (flags & I2C_M_REV_DIR_ADDR )
addr ^= 1;
ret = try_address(i2c_adap, addr, retries);
if ((ret!=1) && !nak_ok)
return -EREMOTEIO;
}
return 0;
}
static int bit_xfer(struct i2c_adapter *i2c_adap,
struct i2c_msg msgs[], int num)
{
struct i2c_msg *pmsg;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
int i,ret;
unsigned short nak_ok;
i2c_start(adap);
for (i=0;i<num;i++) {
pmsg = &msgs[i];
nak_ok = pmsg->flags & I2C_M_IGNORE_NAK;
if (!(pmsg->flags & I2C_M_NOSTART)) {
if (i) {
i2c_repstart(adap);
}
ret = bit_doAddress(i2c_adap, pmsg);
if ((ret != 0) && !nak_ok) {
DEB2(printk(KERN_DEBUG "i2c-algo-bit.o: NAK from device addr %2.2x msg #%d\n"
,msgs[i].addr,i));
goto bailout;
}
}
if (pmsg->flags & I2C_M_RD ) {
/* read bytes into buffer*/
ret = readbytes(i2c_adap, pmsg);
DEB2(printk(KERN_DEBUG "i2c-algo-bit.o: read %d bytes.\n",ret));
if (ret < pmsg->len) {
if (ret >= 0)
ret = -EREMOTEIO;
goto bailout;
}
} else {
/* write bytes from buffer */
ret = sendbytes(i2c_adap, pmsg);
DEB2(printk(KERN_DEBUG "i2c-algo-bit.o: wrote %d bytes.\n",ret));
if (ret < pmsg->len) {
if (ret >= 0)
ret = -EREMOTEIO;
goto bailout;
}
}
}
ret = i;
bailout:
i2c_stop(adap);
return ret;
}
static u32 bit_func(struct i2c_adapter *adap)
{
return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
I2C_FUNC_SMBUS_READ_BLOCK_DATA |
I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
}
/* -----exported algorithm data: ------------------------------------- */
static const struct i2c_algorithm i2c_bit_algo = {
.master_xfer = bit_xfer,
.functionality = bit_func,
};
/*
* registering functions to load algorithms at runtime
*/
static int i2c_bit_prepare_bus(struct i2c_adapter *adap)
{
struct i2c_algo_bit_data *bit_adap = adap->algo_data;
if (bit_test) {
int ret = test_bus(bit_adap, adap->name);
if (ret<0)
return -ENODEV;
}
DEB2(dev_dbg(&adap->dev, "hw routines registered.\n"));
/* register new adapter to i2c module... */
adap->algo = &i2c_bit_algo;
adap->timeout = 100; /* default values, should */
adap->retries = 3; /* be replaced by defines */
return 0;
}
int i2c_bit_add_bus(struct i2c_adapter *adap)
{
int err;
err = i2c_bit_prepare_bus(adap);
if (err)
return err;
return i2c_add_adapter(adap);
}
EXPORT_SYMBOL(i2c_bit_add_bus);
int i2c_bit_add_numbered_bus(struct i2c_adapter *adap)
{
int err;
err = i2c_bit_prepare_bus(adap);
if (err)
return err;
return i2c_add_numbered_adapter(adap);
}
EXPORT_SYMBOL(i2c_bit_add_numbered_bus);
MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
MODULE_DESCRIPTION("I2C-Bus bit-banging algorithm");
MODULE_LICENSE("GPL");
module_param(bit_test, bool, 0);
module_param(i2c_debug, int, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(bit_test, "Test the lines of the bus to see if it is stuck");
MODULE_PARM_DESC(i2c_debug,
"debug level - 0 off; 1 normal; 2,3 more verbose; 9 bit-protocol");
Reference in a new issue View git blame Copy permalink