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SubjectRe: [PATCH V2 2/2] efi/fb: Convert PCI bus address to resource if translated by the bridge
On 20 June 2018 at 00:29, Bjorn Helgaas <helgaas@kernel.org> wrote:
> Minor subject nit: From the caller's point of view, we must convert a bus
> address to a resource *always* (the caller has no knowledge of "whether it
> is translated by the host bridge").
>
> On Fri, May 18, 2018 at 10:17:51AM -0400, Sinan Kaya wrote:
>> A host bridge is allowed to remap BAR addresses using _TRA attribute in
>> _CRS windows.
>
> Also, _TRA/_CRS are ACPI-specific terms and non-ACPI host bridges can
> also do the same sort of translation. Another trivial nit.
>
>> pci_bus 0000:00: root bus resource [mem 0x80100100000-0x8011fffffff window] (bus address [0x00100000-0x1fffffff])
>> pci 0000:02:00.0: reg 0x10: [mem 0x8011e000000-0x8011effffff]
>>
>> When a VGA device is behind such a host bridge and the resource is
>> translated efifb driver is trying to do ioremap against bus address
>> rather than the resource address and is failing to probe.
>>
>> efifb: probing for efifb
>> efifb: cannot reserve video memory at 0x1e000000
>> efifb: framebuffer at 0x1e000000, using 1920k, total 1875k
>> efifb: mode is 800x600x32, linelength=3200, pages=1
>> efifb: scrolling: redraw
>> efifb: Truecolor: size=8:8:8:8, shift=24:16:8:0
>>
>> Use the host bridge offset information to convert bus address to
>> resource address in the fixup.
>>
>> Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
>
> Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
>
> Thanks a lot for fixing this!
>

Apologies for only bringing this up now, but I think this patch is
wrong after all.

screen_info.lfb_base is supposed to be a CPU address, and so
translating it like this is wrong. If you end up with a PCI address
here, you have made a mistake in hacking support for PCI outbound
translations into UEFI. Other users such as UEFI itself or GRUB will
treat this as a CPU physical address as well, so the kernel should not
treat it any differently.


>> ---
>> drivers/video/fbdev/efifb.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
>> index 6daac8d..429cc85 100644
>> --- a/drivers/video/fbdev/efifb.c
>> +++ b/drivers/video/fbdev/efifb.c
>> @@ -431,6 +431,7 @@ static void efifb_fixup_resources(struct pci_dev *dev)
>> .end = screen_info.lfb_base + screen_info.lfb_size - 1,
>> .flags = IORESOURCE_MEM,
>> };
>> + struct pci_bus_region region;
>> int i;
>>
>> if (efifb_pci_dev || screen_info.orig_video_isVGA != VIDEO_TYPE_EFI)
>> @@ -442,6 +443,10 @@ static void efifb_fixup_resources(struct pci_dev *dev)
>> if (!screen_res.start)
>> return;
>>
>> + region.start = screen_res.start;
>> + region.end = screen_res.end;
>> + pcibios_bus_to_resource(dev->bus, &screen_res, &region);
>> +
>> for (i = 0; i <= PCI_STD_RESOURCE_END; i++) {
>> struct resource *res = &dev->resource[i];
>>
>> --
>> 2.7.4
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
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