Re: [Qemu-devel] [PATCH] CMOS file support

[Stefan Weil <weil@mail.berlios.de>]

Am 16.09.2010 15:58, schrieb Mathias Krause:
> In contrast to the BIOS and Option ROMs the CMOS content cannot be
> predefined by the user. Also the amount of useable CMOS ARM is pretty
> limited, even though the amount of CMOS bytes emulated by qemu is
> already twice as much as of the original MC146818. Nevertheless those
> limitations are pretty annoying when testing different BIOS replacement
> implementations like coreboot in combination with FILO that use CMOS
> values above the basic RTC range for its own purpose to, e.g., control
> the boot device order using a string containing the boot devices to
> probe.
>
> This patch adds support to specify a file to read the initial CMOS
> content from. It also increases the CMOS size to 256 bytes and
> implements access to the extended memory range via I/O ports 0x72 and
> 0x73.
>
> Use it like: `qemu -global mc146818rtc.file=cmos.bin ...' where cmos.bin
> is a binary file, sized 256 bytes containing the CMOS RAM.
>
> Signed-off-by: Mathias Krause<mathias.krause@secunet.com>
> ---
>   hw/mc146818rtc.c |   62 ++++++++++++++++++++++++++++++++++++++++++++++++-----
>   1 files changed, 56 insertions(+), 6 deletions(-)
>
>    

[snip]

The intention of this patch is ok. Loading CMOS with initial data
is needed. I just want to add two questions / remarks how the
implementation might be improved.

Are there use cases where having a smaller CMOS size is better?
For example, when I want to emulate a system with 128 byte CMOS?
The size of CMOS could be derived from the size of the data
or specified by an additional parameter.

Using QEMU's block devices instead of a simple file would be
more consistent with the rest of QEMU and allow reading the
CMOS data not only from a file but also from an URL or other
sources.

Regards
Stefan