drivers/spi: reduce confusion in the API

Julius brought up confusion about the current spi api in [1]. In order
alleviate the confusion stemming from supporting x86 spi flash

- Remove spi_xfer_two_vectors() which was fusing transactions to
  accomodate the limitations of the spi controllers themselves.
- Add spi_flash_vector_helper() for the x86 spi flash controllers to
  utilize in validating driver/controller current assumptions.
- Remove the xfer() callback in the x86 spi flash drivers which
  will trigger an error as these controllers can't support the api.


Change-Id: Id88adc6ad5234c29a739d43521c5f344bb7d3217
Signed-off-by: Aaron Durbin <>
Tested-by: build bot (Jenkins) <>
Reviewed-by: Julius Werner <>
15 files changed