This SPI driver adds support for the Aspeed static memory controllers
of the AST2600, AST2500 and AST2400 SoCs using the spi-mem interface.

 * AST2600 Firmware SPI Memory Controller (FMC)
   . BMC firmware
   . 3 chip select pins (CE0 ~ CE2)
   . Only supports SPI type flash memory
   . different segment register interface
   . single, dual and quad mode.

 * AST2600 SPI Flash Controller (SPI1 and SPI2)
   . host firmware
   . 2 chip select pins (CE0 ~ CE1)
   . different segment register interface
   . single, dual and quad mode.

 * AST2500 Firmware SPI Memory Controller (FMC)
   . BMC firmware
   . 3 chip select pins (CE0 ~ CE2)
   . supports SPI type flash memory (CE0-CE1)
   . CE2 can be of NOR type flash but this is not supported by the driver
   . single, dual mode.

 * AST2500 SPI Flash Controller (SPI1 and SPI2)
   . host firmware
   . 2 chip select pins (CE0 ~ CE1)
   . single, dual mode.

 * AST2400 New Static Memory Controller (also referred as FMC)
   . BMC firmware
   . New register set
   . 5 chip select pins (CE0 ∼ CE4)
   . supports NOR flash, NAND flash and SPI flash memory.
   . single, dual and quad mode.

Each controller has a memory range on which flash devices contents are
mapped. Each device is assigned a window that can be changed at bootime
with the Segment Address Registers.

Each SPI flash device can then be accessed in two modes: Command and
User. When in User mode, SPI transfers are initiated with accesses to
the memory segment of a device. When in Command mode, memory
operations on the memory segment of a device generate SPI commands
automatically using a Control Register for the settings.

This initial patch adds support for User mode. Command mode needs a little
more work to check that the memory window on the AHB bus fits the device
size. It will come later when support for direct mapping is added.

Single and dual mode RX transfers are supported. Other types than SPI
are not supported.
Reviewed-by: Joel Stanley <joel@jms.id.au>
Tested-by: Joel Stanley <joel@jms.id.au>
Tested-by: Tao Ren <rentao.bupt@gmail.com>
Tested-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Link: https://lore.kernel.org/r/20220509175616.1089346-4-clg@kaod.orgSigned-off-by: Mark Brown <broonie@kernel.org>