spi: dw: Add support for 32-bits max xfer size

spi: dw: Add support for 32-bits max xfer size

The Synopsis DesignWare DW_apb_ssi specifications version 3.23 onward
define a 32-bits maximum transfer size synthesis parameter
(SSI_MAX_XFER_SIZE=32) in addition to the legacy 16-bits configuration
(SSI_MAX_XFER_SIZE=16) for SPI controllers. When SSI_MAX_XFER_SIZE=32,
the layout of the ctrlr0 register changes, moving the data frame format
field from bits [3..0] to bits [16..20], and the RX/TX FIFO word size
can be up to 32-bits.

To support this new format, introduce the DW SPI capability flag
DW_SPI_CAP_DFS32 to indicate that a controller is configured with
SSI_MAX_XFER_SIZE=32. Since SSI_MAX_XFER_SIZE is a controller synthesis
parameter not accessible through a register, the detection of this
parameter value is done in spi_hw_init() by writing and reading the
ctrlr0 register and testing the value of bits [3..0]. These bits are
ignored (unchanged) for SSI_MAX_XFER_SIZE=16, allowing the detection.
If a DFS32 capable SPI controller is detected, the new field dfs_offset
in struct dw_spi is set to SPI_DFS32_OFFSET (16).

dw_spi_update_config() is modified to set the data frame size field at
the correct position is the CTRLR0 register, as indicated by the
dfs_offset field of the dw_spi structure.

The DW_SPI_CAP_DFS32 flag is also unconditionally set for SPI slave
controllers, e.g. controllers that have the DW_SPI_CAP_DWC_SSI
capability flag set. However, for these ssi controllers, the dfs_offset
field is set to 0 as before (as per specifications).

Finally, for any controller with the DW_SPI_CAP_DFS32 capability flag
set, dw_spi_add_host() extends the value of bits_per_word_mask from
16-bits to 32-bits. dw_reader() and dw_writer() are also modified to
handle 32-bits iTX/RX FIFO words.

Suggested-by: Sean Anderson <seanga2@gmail.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20201206011817.11700-3-damien.lemoal@wdc.com
Signed-off-by: Mark Brown <broonie@kernel.org>