Re: [PATCH 03/10] MdeModulePkg/AtaAtapiPassThru: disable the device at ExitBootServices()

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 26 October 2017 at 15:09, Laszlo Ersek <lersek@redhat.com> wrote:
> Ard, Star,
>
> (CC Igor)
>
> On 10/26/17 07:08, Zeng, Star wrote:
>> Good point.
>>
>> Could we find out what change causes the performance regression? Bus Master disable / Memory Space disable / IO Space disable?
>> How about to only disable Bus Master in the exit boot service event notification? It seems the key point suggested by UEFI Driver_Writer_Guide_V1.0.1_120308.pdf.
>>
>> 7.7
>> Examples from the EDK II that use this feature are the PCI device drivers for USB Host
>> Controllers. Some USB Host Controllers are PCI Bus Masters that continuously access a
>> memory buffer to poll for operation requests. Access to this memory buffer by a USB
>> Host Controller may be required to boot an operation system, but this activity must be
>> terminated when the OS calls ExitBootServices(). *The typical action in the Exit Boot
>> Services Event for these types of drivers is to disable the PCI bus master* and place the
>> USB Host Controller into a halted state
>
> thank you for the ideas.
>
> * Disabling only EFI_PCI_IO_ATTRIBUTE_BUS_MASTER at EBS mitigates the
>   symptom.
>
> * Disabling (EFI_PCI_IO_ATTRIBUTE_BUS_MASTER | EFI_PCI_IO_ATTRIBUTE_IO)
>   at EBS preserves the symptom.
>
> * Disabling
>   (EFI_PCI_IO_ATTRIBUTE_BUS_MASTER | EFI_PCI_IO_ATTRIBUTE_MEMORY) at EBS
>   also mitigates the symptom.
>

Excellent!

> So it is as Ard suspected, disabling IO port decoding is what tickles
> the bug in Windows.
>
> (Now I'm vaguely recalling an earlier discussion from qemu-devel that
> Windows has a bug in that, if any given PCI device is disabled at boot,
> then Windows will not load drivers for it, or some such. I'm struggling
> to recall the context; maybe it was related to ACPI generation in QEMU.
> I'm CC'ing Igor; maybe he remembers better.)
>
> I will post a patch, for disabling EFI_PCI_IO_ATTRIBUTE_BUS_MASTER only.
> First, that's going to follow the driver writers' guide verbatim;
> second, disabling BMDMA and MMIO, but not IO, would look weird in the
> code. :/
>
> Thank you both for the help!

Anytime.