----- Original Message ----- > From: "Wolfram Sang" <wsa@xxxxxxxxxxxxx> > Sent: Friday, December 11, 2015 7:19:40 AM > > On Mon, Nov 16, 2015 at 06:02:19PM -0600, 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(-) > > I remember I had a lengthy discussion with Guenter Roeck about 16 bit > support via smbus. I don't have the bandwidth right now to recap the > discussion and check if the concerns apply to your implementation as > well. Could you check this thread > > https://lkml.org/lkml/2015/2/4/436 > > and report back if it applies to your patch as well? This would speed up > the review significantly. Wolfram, The real bus-level multi-master issue is still present. However, it is documented via comments in the driver and warnings in the Kconfig. The other (and apparently bigger) issue of a single master experiencing corruption due to simultaneous access through i2c-dev and this driver appears to have been resolved. The i2cdump, i2cget, and i2cset utilities refuse to access any device that has a driver bound to it. My attempts to cause corruption using i2cdump were met with the following message until I unregistered the at24 driver from the device: # i2cdump 8 0x54 No size specified (using byte-data access) Error: Could not set address to 0x54: Device or resource busy -Aaron S. -- 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
