On 06/14/2010 09:25 PM, Kevin O'Connor wrote:
On Mon, Jun 14, 2010 at 05:51:27PM +0300, Avi Kivity wrote:
On 06/14/2010 05:09 PM, Gleb Natapov wrote:
Could we just have qemu build the hpet tables and pass them through to seabios? Perhaps using the qemu_cfg_acpi_additional_tables() method.
Possible, and I considered that. I personally prefer to pass minimum information required for seabios to discover underlying HW and leave ACPI table creation to seabios. That is how things done for HW that seabios can actually detect. If we will go your way pretty soon we will move creation of ACPI/SMBIOS/MP tables into qemu and IMHO this will be step backworkds.
I agree. ACPI is a firmware/OS interface. If we move ACPI table generation into qemu, it becomes a mixed hardware/firmware/OS interface.
This seems to be a philosophical distinction. Lets go over the practical implications.
In my experience, well-defined interfaces ("philosophical distinctions") are more important in the long term than practicalities. The practicalities change, but confusion over incorrect interfaces, or problems when wrong interfaces are used, are forever.
It seems there was a change in qemu to the hpet functionality. Although the change is solely between qemu and the OS, it's necessary to patch both qemu and seabios for the OS to see the change. This means creating and reviewing patches for two separate repos. This also requires release coordination - the seabios change has to be committed and released, and then qemu needs to be released with the new seabios. Additional changes in seabios tip will get merged into qemu, which could complicate testing.
If a table needs to refer to some other information which is in a table that is generated by seabios, we cannot generate this table from qemu. That's much worse that reviewing and applying two patches.
Better keep those interfaces separate: hardware/firmware (fwcfg) and firmware/OS (acpi).
One could look at the current hpet patch as implementing: qemu -> struct hpet_fw_entry -> seabios -> struct acpi_20_hpet -> OS.
I'm suggesting that we do the following instead: qemu -> struct acpi_20_hpet -> seabios -> struct acpi_20_hpet -> OS.
I'm not suggesting a radical rethink of fwcfg, but I fail to see the advantage in introducing the arbitrary "struct hpet_fw_entry" when there is a perfectly good, well defined, "struct acpi_20_hpet" that already exists. This new arbitrary intermediate format just introduces "make work" for all of us.
Choosing an existing format is fine. But seabios blindly copying qemu provided data is wrong IMO.