On Mon, 16 Nov 2015 18:02:19 -0600 (CST), Aaron Sierra wrote: > Previously, the at24 driver would bail out in the case of a 16-bit > addressable EEPROM attached to an SMBus controller. This is because > SMBus block reads and writes don't map to I2C multi-byte reads and > writes when the offset portion is 2 bytes. > > Instead of bailing out, this patch settles for functioning with single > byte read SMBus cycles. Writes can be block or single-byte, depending > on SMBus controller features. > > Read access is not without some risk. Multiple SMBus cycles are > required to read even one byte. If the SMBus has multiple masters and > one accesses this EEPROM between the dummy address write and the > subsequent current-address-read cycle(s), this driver will receive > data from the wrong address. > > Functionality has been tested with the following devices: > > AT24CM01 attached to Intel ISCH SMBus > AT24C512 attached to Intel I801 SMBus > > Read performance: > 3.6 KB/s with 32-byte* access > > *limited to 32-bytes by I2C_SMBUS_BLOCK_MAX. > > Write performance: > 248 B/s with 1-byte page (default) > 3.9 KB/s with 128-byte* page (via platform data) > > *limited to 31-bytes by I2C_SMBUS_BLOCK_MAX - 1. > > Signed-off-by: Nate Case <ncase@xxxxxxxxxxx> > Signed-off-by: Aaron Sierra <asierra@xxxxxxxxxxx> > Reviewed-by: Jean Delvare <jdelvare@xxxxxxx> > --- > v2 - Account for changes related to introduction of > i2c_smbus_read_i2c_block_data_or_emulated() > v3 - Consolidate three patches into one > - Expand comments regarding SMBus multi-master read risks. > - Rely on current-address-read for improved read performance (i.e. one > dummy address write followed by multiple individual byte reads). > This improves performance from 1.4 KiB/s to 3.6 KiB/s. > - Use struct at24_data's writebuf instead of kzalloc-ing > - Only limit write_max by 1-byte when accessing a 16-bit device with > block writes instead of attempting to preserve a power-of-two. > - Style fixes (indentation, parentheses, unnecessary masking, etc.) > v4 - Address 16-bit safety in Kconfig > - Set "count" to zero later in at24_smbus_read_block_data() > - Fix over-80-columns issues in at24_eeprom_read() > - Fix write_max off-by-one in at24_probe() > - Check SMBus functionality needed for 16-bit device reads > - Homogenize indentation of SMBus functionality checks for SMBus write > v5 - 16-bit device read needs READ_BYTE not READ_BYTE_DATA > - Clarify write_max limiting with smbus_max > - Add X-ES copyright > v6 - Update comment associated with SMBus functionality testing for 16-bit > device read (READ_BYTE not READ_BYTE_DATA) > > drivers/misc/eeprom/Kconfig | 5 +- > drivers/misc/eeprom/at24.c | 132 +++++++++++++++++++++++++++++++++++++++----- > 2 files changed, 122 insertions(+), 15 deletions(-) > (...) Sweet, thanks for your patience. Now it's up to Wolfram. -- Jean Delvare SUSE L3 Support -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
