mb/qemu-{i440fx,q35}/rom_media.c: add code for writable flash

Depending on how firmware image was passed to QEMU, it may behave as:
- ROM - memory mapped reads, writes are ignored (FW image mounted with
  '-bios');
- RAM - memory mapped reads and writes (FW image mounted with e.g.
  '-device loader');
- flash - memory mapped reads, write and erase possible through
  commands. Contrary to physical flash devices erase is not required
  before writing, but it also doesn't hurt. Flash may be split into
  read-only and read-write parts, like OVMF_CODE.fd and OVMF_VARS.fd.
  Combined size of system firmware must not exceed 8 MiB by default
  (FW image(s) mounted with '-drive if=pflash').

This function detects which of the above applies and fills
region_device_ops accordingly.

Tested by starting QEMU with firmware passed as '-drive if=pflash',
'-drive if=pflash,readonly=on' and '-bios'. When started with firmware
passed through '-device loader', coreboot complains about corrupted
FMAP, but this is the same behavior as without this change:

    [ERROR]  Invalid FMAP at 0x40000
    [EMERG]  Cannot locate primary CBFS

Writable pflash support was added about 17 years ago, so it should be
supported by all QEMU versions currently in use. Since QEMU 5.0.0 it is
possible to change the limit of firmware size with `max-fw-size` machine
configuration option, up to 16 MiB, as bigger sizes would overlap with
default IO APIC memory range.

Change-Id: I3ab9f22c6165064a769881d4be5eab13a0a2f519
Signed-off-by: Krystian Hebel <krystian.hebel@3mdeb.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82555
Reviewed-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Sergii Dmytruk <sergii.dmytruk@3mdeb.com>

0 files changed, 0 insertions, 0 deletions