On 7/2/2018 11:15 AM, Mario.Limonciello@xxxxxxxx wrote: >> >>> I don't believe SMM communication ACPI table has ever been implemented by >> Dell >>> on server or client BIOS. I do agree this table describes the behavior that DCDBAS >> driver >>> has used since before even UEFI BIOS pretty accurately. >> >> So, EPS table has been for ages in Dell machines? >> Can we consider it as a predecessor of that SMM communication ACPI table? > > No, EPS is new this year, specifically for server BIOS to be able to support SMM communication > when WSMT is enabled. The code tests in Stuart's patch will detect if WSMT is enabled > and if it's enabled test if EPS was defined. On server BIOS when EPS is defined dcdbas > will be able to communicate using addresses defined in EPS. > > Server BIOS will support EPS for applications using dcdbas interface and may at a later time > introduce same WMI interface as client too (but applications will need time to update so > they need to support both). > > Actually Stuart's patch will cause client BIOS that has WSMT enabled make dcdbas fail > initialization (as it should because dcdbas doesn't have a region that it can successfully > communicate). > > In client machines we moved this communication to ACPI buffer allocated by WMI, which > is why we have dell-smbios-wmi now in kernel. > > I think once some variation of Stuart's patch is merged, I'll send a follow > up patch to drop this test because it's no longer necessary: > https://github.com/torvalds/linux/blob/master/drivers/platform/x86/dell-smbios-smm.c#L106 > > >> >>> Stuart and I did discuss with server BIOS (who uses this EPS mechanism) to see if >> its possible >>> to move EPS to SMM communication ACPI table however since it's been >> deprecated by >>> UEFI 2.7 they weren't willing to adopt it. >> >> It's pity, but the motivation to deprecate is "lack of use" which is >> not true. That's why I would suggest to escalate this to UEFI >> committee. >> >>> Stuart, anything else you want to add here? >> >> Darren, what's your opinion about this? >> >> P.S. I'm not against this approach (just some technical comments I >> already shared), but on the other hand it would be nice to have undo >> that deprecation and follow the standard in new firmwares. >> Would you agree? > > Sure. Due to the timing of how long this will take, even if SMM communication > ACPI table is undone from deprecation we may have to still support both EPS > and SMM communication ACPI table though (maybe it would be order of preference). > > I have confirmation that the EPS table will be 16-byte aligned, so I can make that change. I'll send a v5 with that and the updated comment.
