On 10/07/15 18:14, Tirdea, Irina wrote: > > >> -----Original Message----- >> From: Jonathan Cameron [mailto:ji...@kernel.org] >> Sent: 05 July, 2015 14:59 >> To: Tirdea, Irina; Wolfram Sang; linux-...@vger.kernel.org; >> linux-...@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org; 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.tir...@intel.com> >> 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." > Works for me. > 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 */ >>> >>> /** >>> >
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