> -----Original Message----- > From: Wolfram Sang [mailto:wsa@xxxxxxxxxxxxx] > Sent: 15 April, 2015 18:55 > To: Tirdea, Irina > Cc: linux-i2c@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [RFC PATCH 1/1] i2c: core: Add support for best effort block read emulation > > On Wed, Mar 25, 2015 at 04:33:20PM +0200, Irina Tirdea wrote: > > There are devices that need to handle block transactions > > regardless of the capabilities exported by the adapter. > > For performance reasons, they need to use i2c read blocks > > if available, otherwise emulate the block transaction with word > > or byte transactions. > > > > Add support for a helper function that would read a data block > > using the best transfer available: I2C_FUNC_SMBUS_READ_I2C_BLOCK, > > I2C_FUNC_SMBUS_READ_WORD_DATA or I2C_FUNC_SMBUS_READ_BYTE_DATA. > > > > Signed-off-by: Irina Tirdea <irina.tirdea@xxxxxxxxx> > > --- > > > > Hi, > > > > This is a new API proposal to handle i2c block emulation in the > > core instead of the driver code. > > > > This is needed for a set of iio sensor changes ([1], [2], [3]) > > that would otherwise duplicate this code. There are also some > > usages of this functionality in the kernel (e.g. eeprom driver at24). > > > > Please let me know what you think. > > I am open to add something like this. One change I'd like to request is > to introduce a user, e.g. convert at24. > Thanks for the review! Sure, I'll send a new version with the fixes you suggested and include a user as well. > > > > Thanks, > > Irina > > > > [1] https://lkml.org/lkml/2015/2/16/408 > > [2] https://lkml.org/lkml/2015/2/16/413 > > [3] https://lkml.org/lkml/2015/2/16/402 > > > > drivers/i2c/i2c-core.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > include/linux/i2c.h | 3 +++ > > 2 files changed, 65 insertions(+) > > > > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c > > index fe80f85..2579f7d 100644 > > --- a/drivers/i2c/i2c-core.c > > +++ b/drivers/i2c/i2c-core.c > > @@ -2907,6 +2907,68 @@ trace: > > } > > EXPORT_SYMBOL(i2c_smbus_xfer); > > > > +/** > > + * i2c_smbus_read_i2c_block_data_or_emulated - read block or emulate > > + * @client: Handle to slave device > > + * @command: Byte interpreted by slave > > + * @length: Size of data block; SMBus allows at most 32 bytes > > + * @values: Byte array into which data will be read; big enough to hold > > + * the data returned by the slave. SMBus allows at most 32 bytes. > > Sidenote: SMBus3 allows 255 byte, but we don't support that (yet), so > this is okay for now. > > > + * > > + * This executes the SMBus "block read" protocol if supported by the adapter. > > + * If block read is not supported, it emulates it using either word or byte > > + * read protocols depending on availability. > > Here I'd like to see a warning that people should double-check if their > I2C slave does support that. Sometimes one can't exchange a block > transfer with a byte transfer. > Ok. > > + */ > > +s32 i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client, > > + u8 command, u8 length, u8 *values) > > +{ > > + u8 i; > > + int status; > > + > > + if (length > I2C_SMBUS_BLOCK_MAX) > > + length = I2C_SMBUS_BLOCK_MAX; > > + > > + if (i2c_check_functionality(client->adapter, > > + I2C_FUNC_SMBUS_READ_I2C_BLOCK)) { > > + return i2c_smbus_read_i2c_block_data(client, command, > > + length, values); > > + } else if (i2c_check_functionality(client->adapter, > > + I2C_FUNC_SMBUS_READ_WORD_DATA | > > + I2C_FUNC_SMBUS_READ_BYTE_DATA)) { > > What about skipping the need for READ_BYTE_DATA and dump the byte which > was maybe read too much? > Yes, that will simply the code. > > + for (i = 0; (i + 2) <= length; i += 2) { > > + status = i2c_smbus_read_word_data(client, command + i); > > + if (status < 0) > > + return status; > > + values[i] = status & 0xff; > > + values[i+1] = status >> 8; > > + } > > + if (i < length) { > > + status = i2c_smbus_read_byte_data(client, command + i); > > + if (status < 0) > > + return status; > > + values[i] = status; > > + i++; > > + } > > + return i; > > + } else if (i2c_check_functionality(client->adapter, > > + I2C_FUNC_SMBUS_READ_BYTE_DATA)) { > > + for (i = 0; i < length; i++) { > > + status = i2c_smbus_read_byte_data(client, command + i); > > + if (status < 0) > > + return status; > > + values[i] = status; > > + } > > + return i; > > + } > > + > > + dev_err(&client->adapter->dev, "Unsupported transactions: %d,%d,%d\n", > > + I2C_SMBUS_I2C_BLOCK_DATA, I2C_SMBUS_WORD_DATA, > > + I2C_SMBUS_BYTE_DATA); > > + > > + return -EOPNOTSUPP; > > +} > > +EXPORT_SYMBOL(i2c_smbus_read_i2c_block_data_or_emulated); > > Thanks, > > Wolfram -- 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
