drivers/spi: Stop using a variable-length array

Only the call in `spi_flash_cmd_write_page_program` uses non-constant
values for the array length. However, the value for `data_len` has an
upper bound: `flash->page_size` is set to `1U << vi->page_size_shift`
which depends on the flash chip vendor info, and the largest value it
can currently have is 8. Thus, the maximum page size is currently 256.

Define the `MAX_FLASH_CMD_DATA_SIZE` macro to place an upper bound on
the amount of data that can be written in one command. Then, use this
value to allocate a fixed-size buffer in `spi_flash_cmd_write`. Also,
add a check to prevent buffer overflow problems. Finally, ensure that
the `spi_flash_cmd_write_page_program` function always writes no more
than 256 bytes of data when using the `spi_flash_cmd_write` function.

Tested on Asrock B85M Pro4 (Winbond W25Q64FV), MRC cache still works.

Change-Id: Ib630bff1b496bc276616989d4506a3c96f242e26
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50480
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

0 files changed, 0 insertions, 0 deletions