Messages in this thread | | | Subject | Re: [PATCH v1 1/1] i2c: iproc: Add i2c repeated start capability | From | Ray Jui <> | Date | Tue, 24 Sep 2019 10:23:12 -0700 |
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Hi Wolfram,
On 9/4/19 2:37 PM, Wolfram Sang wrote: > >> I think you are right that the controller does not seem to support >> additional I2C features in addition to SMBUS. >> >> However, my concern of switching to the smbus_xfer API is: >> >> 1) Some customers might have used I2C_RDWR based API from i2cdev. Changing >> from master_xfer to smbus_xfer may break the existing applications that are >> already developed. > > Well, given that you add new quirks in the original patch here, you are > kind of breaking it already. Most transfers which are not SMBus-alike > transfers would now be rejected. For SMBus-alike transfers which are > sent via I2C_RDWR (which is ugly), I have to think about it. > >> 2) The sound subsystem I2C regmap based implementation seems to be using >> i2c_ based API instead of smbus_ based API. Does this mean this will also >> break most of the audio codec drivers with I2C regmap API based usage? > > I don't think so. If you check regmap_get_i2c_bus() then it checks the > adapter functionality and chooses the best transfer option then. I may > be missing something but I would wonder if the sound system does > something special and different. >
We did more investigation on this.
First of all, like you said, there's no concern on regmap based API, the smbus_xfer only based approach should just work.
Secondly, for most i2ctools like i2cget, i2cset, i2cdump, there's no concern either, given that they already use I2C_SMBUS based IOCTL.
However, for i2ctransfer or any customer applications that use I2C_RDWR IOCTL, i2c_transfer (master_xfer) is the only supported function. And we can confirm we do have at least one customer using i2ctransfer for EEPROM access on their system, e.g., i2ctransfer 1 w2@0x50 0x00 0x00 r64.
In my opinion, it's probably better to continue to support master_xfer in our driver (with obvious limitations), in order to allow i2ctransfer (or any apps that use I2C RDWR) to continue to work.
What do you think?
Regards,
Ray
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