I've been preparing a patch series for Beagle and Overo that detects expansion board configuration information by reading a 128 byte I2C EEPROM on each expansion board.
Using the OMAP I2C driver in its current form takes about 5-6 seconds to read this small number of bytes! Executing the i2c probe command takes close to 10 seconds.
Examining the code I see that there are a large number of fairly long udelay calls throughout the driver (10 - 50 milliseconds). I looked through the linux driver and did not see equivalent delays in that code. In fact the longest delay in the linux code was one millisecond.
In looking at the TRM I2C section for OMAP3 and OMAP4 I don't see any requirement for delays in the programming model description.
This patch restructures the i2c driver to eliminate most of the udelay calls by monitoring state changes in the status register.
The EEPROM reads and the i2c probe execution are now instantaneous.
This patch series was tested on OMAP3 (Overo) and OMAP4 (Panda). I do not have access to OMAP2 hardware for testing.
Steve Sakoman (4): ARMV7: OMAP: I2C driver: Use same timeout value as linux kernel driver ARMV7: OMAP: I2C driver: Restructure i2c_read_byte function ARMV7: OMAP: I2C driver: Restructure i2c_write_byte function ARMV7: OMAP: I2C driver: Restructure i2c_probe function
drivers/i2c/omap24xx_i2c.c | 204 ++++++++++++++++++++++++------------------- 1 files changed, 114 insertions(+), 90 deletions(-)