[PATCH] i2c: add EFI i2c master driver

[Sascha Hauer]

Hi Tomas,

Thanks for the patch. Looks mostly fine, but this needs fixing:

On Wed, Mar 20, 2024 at 01:55:38PM +0100, Tomas Marek wrote:
> +static int efi_i2c_xfer(struct i2c_adapter *adapter,
> +			struct i2c_msg *msg, int nmsgs)
> +{
> +	struct efi_i2c_priv *i2c_priv = adapter_to_efi_i2c_priv(adapter);
> +	int i, ret;
> +
> +	for (i = nmsgs; i > 0; i--, msg++) {
> +		ret = efi_i2c_message_xfer(i2c_priv, msg);
> +		if (ret)
> +			return ret;
> +	}

Each of the messages should start with a (repeated) start bit and only
the last message should be followed by a stop bit. By separating the
full message into segments and pushing each segment into EFI separately
you would instead send a stop bit after each segment, see the comment
above EFI_I2C_REQUEST_PACKET:

///
/// I2C device request
///
/// The EFI_I2C_REQUEST_PACKET describes a single I2C transaction.  The
/// transaction starts with a start bit followed by the first operation
/// in the operation array.  Subsequent operations are separated with
/// repeated start bits and the last operation is followed by a stop bit
/// which concludes the transaction.  Each operation is described by one
/// of the elements in the Operation array.
///

Instead you have to compile all nmsgs into a single EFI_I2C_REQUEST_PACKET
and push it into EFI as a single request.

Sascha

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