> -----Original Message----- > From: Jonathan Cameron [mailto:jic23@xxxxxxxxxx] > Sent: 05 July, 2015 14:59 > To: Tirdea, Irina; Wolfram Sang; linux-iio@xxxxxxxxxxxxxxx; linux-i2c@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx; Pandruvada, Srinivas; Peter Meerwald > Subject: Re: [PATCH v3 1/8] i2c: core: Add support for best effort block read emulation > > On 03/07/15 10:33, 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> > Looks good to me - I vaguely wondered if it would make sense to use > an endian conversion in the word case, but as we have possible odd > numbers of bytes that gets fiddly. > Thanks for the review, Jonathan! > I wonder what devices do if you do a word read beyond their end address? > Perhaps in odd cases we should always fall back to byte reads? In my tests I can read beyond the end address, but I cannot be sure if this is OK for all devices. This was actually a suggestion from Wolfram for v1, but maybe I'm missing something. Wolfram, is it safe to read one byte beyond the end address or should I better use only byte reads for odd lengths? > > > --- > > drivers/i2c/i2c-core.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > include/linux/i2c.h | 3 +++ > > 2 files changed, 63 insertions(+) > > > > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c > > index 96771ea..55a3455 100644 > > --- a/drivers/i2c/i2c-core.c > > +++ b/drivers/i2c/i2c-core.c > > @@ -2914,6 +2914,66 @@ 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. > > + * > > + * 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. > > + * > > + * Before using this function you must double-check if the I2C slave does > > + * support exchanging a block transfer with a byte transfer. > Add something here about addressing assumptions. You get odd devices which > will give bulk reads of addresses not mapped to a nice linear region when > you do byte reads. OK, I'll add this to the comment above: "The addresses of the I2C slave device that are accessed with this function must be mapped to a linear region, so that a block read will have the same effect as a byte read." Thanks, Irina > > + */ > > +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)) { > > + for (i = 0; i < length; i += 2) { > > + status = i2c_smbus_read_word_data(client, command + i); > > + if (status < 0) > > + return status; > > + values[i] = status & 0xff; > > + if ((i + 1) < length) > > + values[i + 1] = status >> 8; > > + } > > + if (i > length) > > + return length; > > + 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); > > + > > #if IS_ENABLED(CONFIG_I2C_SLAVE) > > int i2c_slave_register(struct i2c_client *client, i2c_slave_cb_t slave_cb) > > { > > diff --git a/include/linux/i2c.h b/include/linux/i2c.h > > index e83a738..faf518d 100644 > > --- a/include/linux/i2c.h > > +++ b/include/linux/i2c.h > > @@ -121,6 +121,9 @@ extern s32 i2c_smbus_read_i2c_block_data(const struct i2c_client *client, > > extern s32 i2c_smbus_write_i2c_block_data(const struct i2c_client *client, > > u8 command, u8 length, > > const u8 *values); > > +extern s32 > > +i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client, > > + u8 command, u8 length, u8 *values); > > #endif /* I2C */ > > > > /** > > -- 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
