> -----Original Message----- > From: Wolfram Sang [mailto:wsa@xxxxxxxxxxxxx] > Sent: 09 August, 2015 10:32 > To: Tirdea, Irina > Cc: Jonathan Cameron; linux-iio@xxxxxxxxxxxxxxx; linux-i2c@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Pandruvada, Srinivas; > Peter Meerwald > Subject: Re: [PATCH v4 1/8] i2c: core: Add support for best effort block read emulation > > On Tue, Aug 04, 2015 at 05:04:09PM +0300, 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> > > We are close, but I think there is one optimization left to do. > > > +/** > > + * 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 > > Please refer to I2C_SMBUS_BLOCK_MAX instead of 32. The new SMBus specs > increased this amount to 256. (Yes, we don't support that yet.) > Sure, I'll use I2C_SMBUS_BLOCK_MAX instead to be compatible with these changes. > > + * @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. > > + * > > + * 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. Before using this function you must double-check > > + * if the I2C slave does support exchanging a block transfer with a byte > > + * transfer. > > + */ > > +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); > > + > > + if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_WORD_DATA | > > + I2C_FUNC_SMBUS_READ_BYTE_DATA)) { > > + 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; > > + } > > + > > + 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; > > + } > > We have two very similar blocks for transferring READ_BYTE_DATA now. > What about this pseudo code: > > if (check_func(I2C_BLOCK)) > return i2c_smbus_read_i2c_block_data(...); > > if (!check_func(I2C_READ_BYTE_DATA) > return -EOPNOTSUPP; > > if (check_func(I2C_READ_WORD_DATA) > read_as_many_words_as_possible; > > read_all_the_remaining_bytes; > This looks better, so I will change the code following the pseudo code above. > > > + dev_err(&client->adapter->dev, "Unsupported transactions\n"); > > Again, if you want to keep this one, it should be the client device > reporting the error. > Sorry, I misread your previous comment on the device reporting the error. I thought you'd prefer the code that calls i2c_smbus_read_i2c_block_data_or_emulated to print any error messages, but I was not sure. Anyway, I think I'll drop the error message entirely and leave error handling to the calling code. Thanks, Irina > Thanks, > > Wolfram -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
