> -----Original Message-----
> From: Wolfram Sang [mailto:[email protected]]
> Sent: 09 August, 2015 10:32
> To: Tirdea, Irina
> Cc: Jonathan Cameron; [email protected]; [email protected];
> [email protected]; 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 <[email protected]>
>
> 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
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