Linux2.6.21 reading core notes at91_i2c

Linux 2.6.21 read core notes at91_i2c-Linux general technology-Linux programming and kernel information. The following is a detailed description. In the use of linux 2.6.21 in at91rm9200 (Atmel), it seems that i2c is not very good and sometimes unreliable!
Errors may occur after thousands of reads and writes. However, note the following:

A. at91rm9200 datasheet Page396 requirements are as follows:
• Program the PIO controller:
? Dedicate TWD and TWCK as peripheral lines.
? Define TWD and TWCK as open-drain.
In linux 2.6.21, how does one implement kernel?
2.6.21 is different from 2.4.18 in many systems, such as initializing this part 2.4.18 in kernel_source_root/drivers/i2c/, while 2.6.21 in kernel_source_root/Arch/arm/Mach-at91/At91rm9200_devices.c.

/*--------------------------------------------------------------------
* TWI (i2c)
*--------------------------------------------------------------------*/

# If defined (CONFIG_I2C_AT91) | defined (CONFIG_I2C_AT91_MODULE)

Static struct resource twi_resources [] = {
[0] = {
. Start = AT91RM9200_BASE_TWI,
. End = AT91RM9200_BASE_TWI + SZ_16K-1,
. Flags = IORESOURCE_MEM,
},
[1] = {
. Start = AT91RM9200_ID_TWI,
. End = AT91RM9200_ID_TWI,
. Flags = IORESOURCE_IRQ,
},
};

Static struct platform_device at91rm9200_twi_device = {
. Name = "at91_i2c ",
. Id =-1,
. Resource = twi_resources,
. Num_resources = ARRAY_SIZE (twi_resources ),
};

Void _ init at91_add_device_i2c (void)
{
/* Pins used for TWI interface */
At91_set_A_periph (AT91_PIN_PA25, 0);/* TWD */
At91_set_multi_drive (AT91_PIN_PA25, 1 );

At91_set_A_periph (AT91_PIN_PA26, 0);/* TWCK */
At91_set_multi_drive (AT91_PIN_PA26, 1 );

Platform_device_register (& at91rm9200_twi_device );
}
# Else
Void _ init at91_add_device_i2c (void ){}
# Endif

The at91_add_device_i2c () function completes the initialization of at91 i2c. Let's give the definition of the two functions.

/*
* Mux the pin to the "A" internal peripheral role.
*/
Int _ init_or_module at91_set_A_periph (unsigned pin, int use_pullup)
{
Void _ iomem * pio = pin_to_controller (pin );
Unsigned mask = pin_to_mask (pin );

If (! Pio)
Return-EINVAL;

_ Raw_writel (mask, pio + PIO_IDR );
_ Raw_writel (mask, pio + (use_pullup? PIO_PUER: PIO_PUDR ));
_ Raw_writel (mask, pio + PIO_ASR );
_ Raw_writel (mask, pio + PIO_PDR );
Return 0;
}
Obviously: at91_set_A_periph assigns the pin the PeriphA function and marks it by use_pullup.

Int _ init_or_module at91_set_multi_drive (unsigned pin, int is_on)
{
Void _ iomem * pio = pin_to_controller (pin );
Unsigned mask = pin_to_mask (pin );

If (! Pio)
Return-EINVAL;

_ Raw_writel (mask, pio + (is_on? PIO_MDER: PIO_MDDR ));
Return 0;
}
While at91_set_multi_drive (unsigned pin, int is_on) sets whether the pin can be used in multiple functions.