Messages in this thread | | | Date | Sat, 30 Apr 2016 22:17:38 +0100 | From | Matt Fleming <> | Subject | Re: [PATCH] arm64: Relocate screen_info.lfb_base on PCI BAR allocation |
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(Pulling in efifb maintainer, Peter)
On Fri, 29 Apr, at 06:31:19PM, Bjorn Helgaas wrote: > > The efifb.c driver doesn't do anything at all with PCI (it includes > linux/pci.h, but probably doesn't need it). That's part of what I'm > suggesting -- if it *did* register as a PCI device driver, then it > would look at pci_dev->resource[n], which is populated by the PCI > core based on the BAR values.
This discussion came up recently here,
https://lkml.kernel.org/r/20160216151859.GB11373@redhat.com
There's nothing PCI-specific about the EFI framebuffer per se, but in practice it's always a PCI device.
> Is ConOut what you're after? I.e., is the whole point of this > exercise to get a framebuffer driver attached to the device that was > the firmware console? I would think the ConOut path should be > decodable -- it has to tell you how to navigate the interconnect from > the CPU to the device. But I don't know how to do it. > > It looks like on x86, at least, setup_gop32()/setup_gop64() might be > extracting the framebuffer address from the ConOut device and stuffing > it into screen_info, which is what efifb.c later looks at (maybe this > is what Ard was referring to).
Matthew Garrett wrote the x86 code for guessing where the console is. We look for the ConOut protocol with a fallback to first GOP device if we can't find it. I think the heuristic was based on reading the implementation in EDK2. See commit 38cb5ef4473c ("X86: Improve GOP detection in the EFI boot stub").
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