linux-kernel - Re: [PATCH V2 2/2] efi/fb: Convert PCI bus address to resource if translated by the bridge

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Message-ID: <CAKv+Gu_voOZ7YUL8pckww4mTt4PVcu7y69mf-z7ZZe1bJ81Shw@mail.gmail.com>
Date:   Fri, 22 Jun 2018 13:21:29 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Sinan Kaya <okaya@...eaurora.org>,
        "open list:EFIFB FRAMEBUFFER DRIVER" <linux-fbdev@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-arm-msm@...r.kernel.org, Timur Tabi <timur@...eaurora.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:FRAMEBUFFER LAYER" <dri-devel@...ts.freedesktop.org>,
        Peter Jones <pjones@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: 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 <helgaas@...nel.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@...eaurora.org>
>
> Reviewed-by: Bjorn Helgaas <bhelgaas@...gle.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@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
> _______________________________________________
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> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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