Re: [PATCH kernel] powerpc/pci/of: Fix OF flags parsing for 64bit BARs

[Michael Ellerman <patch-notifications@ellerman.id.au>]

On Wed, 2019-06-05 at 03:38:14 UTC, Alexey Kardashevskiy wrote:
> When the firmware does PCI BAR resource allocation, it passes the assigned
> addresses and flags (prefetch/64bit/...) via the "reg" property of
> a PCI device device tree node so the kernel does not need to do
> resource allocation.
> 
> The flags are stored in resource::flags - the lower byte stores
> PCI_BASE_ADDRESS_SPACE/etc bits and the other bytes are IORESOURCE_IO/etc.
> Some flags from PCI_BASE_ADDRESS_xxx and IORESOURCE_xxx are duplicated,
> such as PCI_BASE_ADDRESS_MEM_PREFETCH/PCI_BASE_ADDRESS_MEM_TYPE_64/etc.
> When parsing the "reg" property, we copy the prefetch flag but we skip
> on PCI_BASE_ADDRESS_MEM_TYPE_64 which leaves the flags out of sync.
> 
> The missing IORESOURCE_MEM_64 flag comes into play under 2 conditions:
> 1. we remove PCI_PROBE_ONLY for pseries (by hacking pSeries_setup_arch()
> or by passing "/chosen/linux,pci-probe-only");
> 2. we request resource alignment (by passing pci=resource_alignment=
> via the kernel cmd line to request PAGE_SIZE alignment or defining
> ppc_md.pcibios_default_alignment which returns anything but 0). Note that
> the alignment requests are ignored if PCI_PROBE_ONLY is enabled.
> 
> With 1) and 2), the generic PCI code in the kernel unconditionally
> decides to:
> - reassign the BARs in pci_specified_resource_alignment() (works fine)
> - write new BARs to the device - this fails for 64bit BARs as the generic
> code looks at IORESOURCE_MEM_64 (not set) and writes only lower 32bits
> of the BAR and leaves the upper 32bit unmodified which breaks BAR mapping
> in the hypervisor.
> 
> This fixes the issue by copying the flag. This is useful if we want to
> enforce certain BAR alignment per platform as handling subpage sized BARs
> is proven to cause problems with hotplug (SLOF already aligns BARs to 64k).
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> Reviewed-by: Sam Bobroff <sbobroff@linux.ibm.com>
> Reviewed-by: Oliver O'Halloran <oohall@gmail.com>
> Reviewed-by: Shawn Anastasio <shawn@anastas.io>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/df5be5be8735ef2ae80d5ae1f2453cd81a035c4b

cheers