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linux: Fast Linux MCU i2c_read() with I2C_RDRW (#6101) 

Reading an I2C device from the Linux MCU used a separate write(2)
to select the target register & read(2) to get the value(s). This
implementation uses ioctl(file, I2C_RDWR, ...) to skip a large bus idle
period and extra process sleep by combining them like the stm32.

I2C_RDRW requires I2C_FUNC_I2C flag in the I2C driver. I2C_FUNC_I2C
is defined in:

BCM2835: Pi 1 Models A, A+, B, B+, the Raspberry Pi Zero, the
    Raspberry Pi Zero W, and the Raspberry Pi Compute Module 1
BCM2836: Pi 2 Model B
    Identical to BCM2835 except Cortex
BCM2837: Pi 3 Model B, later models of the Raspberry Pi 2 Model B,
    and the Raspberry Pi Compute Module 3
BCM2837B0: Pi 3 Models A+, B+, and the Raspberry Pi Compute Module 3+
BCM2711: Pi 4 Model B, the Raspberry Pi 400, and the Raspberry Pi
    Compute Module 4
RK3xxx: Rockchips SoCs NanoPi, RockPi, Tinker, etc.
SUNXI: H2, H3, etc. Orange Pi
AMLOGIC: S905x, Banana Pi, Odroid, etc.
TEGRA: NVidia Jetson etc.
MediaTek: Several SBCs in other ranges

Signed-off-by: Matthew Swabey <matthew@swabey.org>
This commit is contained in:
Dr. Matthew Swabey 2023-03-14 21:03:07 -04:00 committed by GitHub
parent ca6e5fe514
commit 9d77f44995
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 34 additions and 8 deletions
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1
src/linux/gpio.h
View File

@ -45,6 +45,7 @@ void gpio_pwm_write(struct gpio_pwm g, uint16_t val);
struct i2c_config { struct i2c_config {
int fd; int fd;
uint8_t addr;
}; };
struct i2c_config i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr); struct i2c_config i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr);

41
src/linux/i2c.c
View File

@ -4,7 +4,8 @@
// //
// This file may be distributed under the terms of the GNU GPLv3 license. // This file may be distributed under the terms of the GNU GPLv3 license.
#include <fcntl.h> // open #include <fcntl.h> // open
#include <linux/i2c-dev.h> // I2C_SLAVE #include <linux/i2c-dev.h> // I2C_SLAVE i2c_msg
#include <linux/i2c.h> // i2c_rdwr_ioctl_data I2C_M_RD I2C_FUNC_I2C
#include <stdio.h> // snprintf #include <stdio.h> // snprintf
#include <sys/ioctl.h> // ioctl #include <sys/ioctl.h> // ioctl
#include <unistd.h> // write #include <unistd.h> // write
@ -42,6 +43,13 @@ i2c_open(uint32_t bus, uint8_t addr)
report_errno("open i2c", fd); report_errno("open i2c", fd);
goto fail; goto fail;
} }
// Test for I2C_RDWR support
unsigned long i2c_funcs; // datatype from ioctl spec.
ioctl(fd, I2C_FUNCS, &i2c_funcs);
if ((i2c_funcs & I2C_FUNC_I2C) == 0) {
report_errno("i2c does not support I2C_RDWR", fd);
goto fail;
}
int ret = ioctl(fd, I2C_SLAVE, addr); int ret = ioctl(fd, I2C_SLAVE, addr);
if (ret < 0) { if (ret < 0) {
report_errno("ioctl i2c", fd); report_errno("ioctl i2c", fd);
@ -73,7 +81,7 @@ i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr)
// dtparam=i2c_baudrate=<rate> // dtparam=i2c_baudrate=<rate>
int fd = i2c_open(bus, addr); int fd = i2c_open(bus, addr);
return (struct i2c_config){.fd=fd}; return (struct i2c_config){.fd=fd, .addr=addr};
} }
void void
@ -91,12 +99,29 @@ void
i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg
, uint8_t read_len, uint8_t *data) , uint8_t read_len, uint8_t *data)
{ {
if(reg_len != 0) struct i2c_rdwr_ioctl_data i2c_data;
i2c_write(config, reg_len, reg); struct i2c_msg msgs[2];
int ret = read(config.fd, data, read_len);
if (ret != read_len) { if(reg_len != 0) {
if (ret < 0) msgs[0].addr = config.addr;
report_errno("read value i2c", ret); msgs[0].flags = 0x0;
msgs[0].len = reg_len;
msgs[0].buf = reg;
i2c_data.nmsgs = 2;
i2c_data.msgs = &msgs[0];
} else {
i2c_data.nmsgs = 1;
i2c_data.msgs = &msgs[1];
}
msgs[1].addr = config.addr;
msgs[1].flags = I2C_M_RD;
msgs[1].len = read_len;
msgs[1].buf = data;
int ret = ioctl(config.fd, I2C_RDWR, &i2c_data);
if(ret < 0) {
try_shutdown("Unable to read i2c device"); try_shutdown("Unable to read i2c device");
} }
} }