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Re: [Qemu-devel] [RFC v5 0/6] pci_expander_brdige: support separate pci

From: Marcel Apfelbaum
Subject: Re: [Qemu-devel] [RFC v5 0/6] pci_expander_brdige: support separate pci domain for pxb-pcie
Date: Thu, 20 Sep 2018 09:42:34 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

Hi Zihan, Gerd

On 09/20/2018 09:09 AM, Gerd Hoffmann wrote:
As for the management, will some checks when adding mcfg be enough for
management? Or I can maintain a variable to indicate how many space
have been consumed and warn the user if they exceed the threshold?
The latter allows us to do the check when the pxb-pcie is initializing.
I think qemu should not apply any restrictions here.
But will that confuse users when their device is not listed in guest os
while qemu does not throw any error/warning?
Well, that can happen anyway.  For example when using an old seabios
version without pci domain support, or other firmware without pci domain
support (coreboot, ovmf).  And there is no easy way for qemu to figure
this beforehand.

You can detect this later, when generating the acpi tables, that there
are expander bridges where the hidden pci bar wasn't configured by the
firmware.  Logging a warning in that case - pointing out the missing
firmware support - is probably a good idea.

Logging a warning if the pxb-pci was not configured is enough I think.
It will also help in case QEMU uses other firmware not supporting
multiple PCI domains at all, e.g. OVMF  (for now), or an older SeaBIOS.



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