RE: Memory and IO space Enabling different in x86 and ARM64

[Bharat Kumar Gogada]

> Subject: Re: Memory and IO space Enabling different in x86 and ARM64
>
> On Fri, Jul 15, 2016 at 08:29:49AM +0000, Bharat Kumar Gogada wrote:
> > Hi,
> >
> > I observe that memory and IO space are enabled by BIOS in x86.
> >
> > In ARM64 we need to call pci_enable_device form End Point to enable
> these resources.
> >
> > Why the resource enablement is different in x86 and ARM64 ?
>
> A portable driver should call pci_enable_device() if it needs access
> to any BARs.  As you've observed, the command register enable bits may
> be set differently on different architectures, and the PCI core
> doesn't set them automatically for you, so the driver can't rely on
> their initial settings.
>
> One reason why Linux doesn't enable them automatically before calling
> the driver's probe method is that it may not be possible to allocate
> space for all the BARs (e.g., if the platform doesn't support I/O port
> space, or if we just run out of space), but the driver may be able to
> operate the device even without all the BARs.
>
Thanks Bjorn


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