[S] Change in coreboot[main]: drivers/spi: Stop using a variable-length array, 2nd try

[Arthur Heymans (Code Review)]

Attention is currently required from: Angel Pons, Arthur Heymans, Elyes Haouas, Felix Held, Julius Werner.

Hello Angel Pons, Elyes Haouas, Felix Held, Julius Werner, Nico Huber, build bot (Jenkins),

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

https://review.coreboot.org/c/coreboot/+/84059?usp=email

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

Change subject: drivers/spi: Stop using a variable-length array, 2nd try
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drivers/spi: Stop using a variable-length array, 2nd try

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.

The buffer is placed in .bss so that it does not increase stack usage in
some use cases.

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

Repost of 59626b86 with 'static' so that the buffer is in bss.

Change-Id: I157ecec69c049ead06467b0328efd7d1a09bd268
Signed-off-by: Angel Pons 
Signed-off-by: Arthur Heymans 
---
M src/drivers/spi/spi_flash.c
M src/drivers/spi/spi_flash_internal.h
2 files changed, 9 insertions(+), 8 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/59/84059/3