From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from saturn.retrosnub.co.uk ([178.18.118.26]:59019 "EHLO saturn.retrosnub.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946068AbbHHPUV (ORCPT ); Sat, 8 Aug 2015 11:20:21 -0400 Subject: Re: [PATCH v4 1/8] i2c: core: Add support for best effort block read emulation To: Irina Tirdea , Wolfram Sang , linux-iio@vger.kernel.org, linux-i2c@vger.kernel.org References: <1438697056-2946-1-git-send-email-irina.tirdea@intel.com> <1438697056-2946-2-git-send-email-irina.tirdea@intel.com> Cc: linux-kernel@vger.kernel.org, Srinivas Pandruvada , Peter Meerwald From: Jonathan Cameron Message-ID: <55C61E33.1020205@kernel.org> Date: Sat, 8 Aug 2015 16:20:19 +0100 MIME-Version: 1.0 In-Reply-To: <1438697056-2946-2-git-send-email-irina.tirdea@intel.com> Content-Type: text/plain; charset=windows-1252 Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On 04/08/15 15:04, 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 I like this a lot. Reviewed-by: Jonathan Cameron > --- > drivers/i2c/i2c-core.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/i2c.h | 3 +++ > 2 files changed, 68 insertions(+) > > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c > index c83e4d1..79ba6a8 100644 > --- a/drivers/i2c/i2c-core.c > +++ b/drivers/i2c/i2c-core.c > @@ -2942,6 +2942,71 @@ 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. > + * > + * 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; I was about to suggest we knew we were word aligned for both elements and hence could use an endian conversion, but I guess we don't know that as values might not be word aligned. Hence what you have is the best we can do! > + } > + 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; > + } > + > + dev_err(&client->adapter->dev, "Unsupported transactions\n"); > + > + 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 */ > > /** >