Re: [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 [off-list ref] 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:

quoted

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.

quoted

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, linelength200, pages=1
efifb: scrolling: redraw
efifb: Truecolor: size=8:8:8:8, shift$:16:8:0

Use the host bridge offset information to convert bus address to
resource address in the fixup.

Signed-off-by: Sinan Kaya <redacted>

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.

quoted

---
 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


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