Re: [PATCH] MdeModulePkg/AtaAtapiPassThru: disable only BM-DMA at ExitBootServices()

["Ni, Ruiyu" <ruiyu.ni@intel.com>]

Maybe win10 does some optimization in S4 path.

Sent from a small-screen device

在 2017年11月24日，上午8:01，Paolo Bonzini <pbonzini@redhat.com<mailto:pbonzini@redhat.com>> 写道：

On 23/11/2017 14:08, Laszlo Ersek wrote:
On 11/23/17 03:20, Ni, Ruiyu wrote:
I cannot explain precisely why the S4 resume fails.
I can just guess: Windows might have some assumptions on the BM bit.
Can we make this configurable on the platform level somehow?

On one hand, I certainly don't want to break Windows 10, even in case
this issue ultimately turns out to be a Windows 10 bug.

On the other hand, OVMF does not support S4, and disabling BMDMA at
ExitBootServices() in PCI drivers is specifically what the Driver
Writers' Guide recommends. Otherwise pending DMA could corrupt OS memory.

S4 can be done by the OS even if firmware says it doesn't support it.

Once hibernation is done, it is merely a "courtesy" for the OSPM to turn
off the computer using the _S4 ACPI object rather than _S5.

Paolo