Change in coreboot[master]: drivers/spi: Stop using a variable-length array

[Angel Pons (Code Review)]

Hello build bot (Jenkins), Patrick Georgi, Paul Menzel, Julius Werner, Jacob Garber,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/50480

to look at the new patch set (#3).

Change subject: drivers/spi: Stop using a variable-length array
......................................................................

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 
---
M src/drivers/spi/spi_flash.c
M src/drivers/spi/spi_flash_internal.h
2 files changed, 8 insertions(+), 8 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/80/50480/3