On Thu, Oct 12, 2017 at 12:24:10PM +0100, Julien Thierry wrote: > Hi Bjorn, > > On 06/10/17 23:24, Bjorn Helgaas wrote: > >From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > > >Daniel Axtens reported that on the HiSilicon D05 board, the VGA device is > >behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so the VGA arbiter > >never selects it as the default, which means Xorg auto-detection doesn't > >work. > > > >VGA is a legacy PCI feature: a VGA device can respond to addresses, e.g., > >[mem 0xa0000-0xbffff], [io 0x3b0-0x3bb], [io 0x3c0-0x3df], etc., that are > >not configurable by BARs. Consequently, multiple VGA devices can conflict > >with each other. The VGA arbiter avoids conflicts by ensuring that those > >legacy resources are only routed to one VGA device at a time. > > > >The arbiter identifies the "default VGA" device, i.e., a legacy VGA device > >that was used by boot firmware. It selects the first device that: > > > > - is of PCI_CLASS_DISPLAY_VGA, > > - has both PCI_COMMAND_IO and PCI_COMMAND_MEMORY enabled, and > > - has PCI_BRIDGE_CTL_VGA set in all upstream bridges. > > > >Some systems don't have such a device. For example, if a host bridge > >doesn't support I/O space, PCI_COMMAND_IO probably won't be enabled for any > >devices below it. Or, as on the HiSilicon D05, the VGA device may be > >behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so accesses to the > >legacy VGA resources will never reach the device. > > > >This patch extends the arbiter so that if it doesn't find a device that > >meets all the above criteria, it selects the first device that: > > > > - is of PCI_CLASS_DISPLAY_VGA and > > - has PCI_COMMAND_IO or PCI_COMMAND_MEMORY enabled > > > >If it doesn't find even that, it selects the first device that: > > > > - is of class PCI_CLASS_DISPLAY_VGA. > > > >Such a device may not be able to use the legacy VGA resources, but most > >drivers can operate the device without those. Setting it as the default > >device means its "boot_vga" sysfs file will contain "1", which Xorg (via > >libpciaccess) uses to help select its default output device. > > > >This fixes Xorg auto-detection on some arm64 systems (HiSilicon D05 in > >particular; see the link below). > > > >It also replaces the powerpc fixup_vga() quirk, albeit with slightly > >different semantics: the quirk selected the first VGA device we found, and > >overrode that selection with any enabled VGA device we found. If there > >were several enabled VGA devices, the *last* one we found would become the > >default. > > > >The code here instead selects the *first* enabled VGA device we find, and > >if none are enabled, the first VGA device we find. > > > >Link: http://lkml.kernel.org/r/20170901072744.2409-1-dja@xxxxxxxxxx > >Tested-by: Daniel Axtens <dja@xxxxxxxxxx> # arm64, ppc64-qemu-tcg > >Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > >--- > > arch/powerpc/kernel/pci-common.c | 12 ------------ > > drivers/gpu/vga/vgaarb.c | 25 +++++++++++++++++++++++++ > > 2 files changed, 25 insertions(+), 12 deletions(-) > > > >diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c > >index 02831a396419..0ac7aa346c69 100644 > >--- a/arch/powerpc/kernel/pci-common.c > >+++ b/arch/powerpc/kernel/pci-common.c > >@@ -1740,15 +1740,3 @@ static void fixup_hide_host_resource_fsl(struct pci_dev *dev) > > } > > DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MOTOROLA, PCI_ANY_ID, fixup_hide_host_resource_fsl); > > DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_FREESCALE, PCI_ANY_ID, fixup_hide_host_resource_fsl); > >- > >-static void fixup_vga(struct pci_dev *pdev) > >-{ > >- u16 cmd; > >- > >- pci_read_config_word(pdev, PCI_COMMAND, &cmd); > >- if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device()) > >- vga_set_default_device(pdev); > >- > >-} > >-DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_ANY_ID, PCI_ANY_ID, > >- PCI_CLASS_DISPLAY_VGA, 8, fixup_vga); > >diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c > >index 76875f6299b8..aeb41f793ed4 100644 > >--- a/drivers/gpu/vga/vgaarb.c > >+++ b/drivers/gpu/vga/vgaarb.c > >@@ -1468,6 +1468,31 @@ static int __init vga_arb_device_init(void) > > vgaarb_info(dev, "no bridge control possible\n"); > > } > >+ if (!vga_default_device()) { > >+ list_for_each_entry(vgadev, &vga_list, list) { > >+ struct device *dev = &vgadev->pdev->dev; > >+ u16 cmd; > >+ > >+ pdev = vgadev->pdev; > >+ pci_read_config_word(pdev, PCI_COMMAND, &cmd); > >+ if (cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) { > >+ vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n"); > >+ vga_set_default_device(pdev); > >+ break; > >+ } > >+ } > >+ } > >+ > >+ if (!vga_default_device()) { > >+ vgadev = list_first_entry_or_null(&vga_list, > >+ struct vga_device, list); > >+ if (vgadev) { > >+ struct device *dev = &vgadev->pdev->dev; > >+ vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n"); > >+ vga_set_default_device(pdev); > > Isn't 'pdev' NULL here? shouldn't it be vgadev->pdev instead? Yes, vgadev->pdev is what I intended, thanks a lot for pointing that out! Bjorn
