From mboxrd@z Thu Jan 1 00:00:00 1970 From: julien.thierry@arm.com (Julien Thierry) Date: Thu, 12 Oct 2017 13:56:32 +0100 Subject: [PATCH 1/2] vgaarb: Select a default VGA device even if there's no legacy VGA In-Reply-To: <20171012140548.10754506@karo-electronics.de> References: <20171006221358.12211.42879.stgit@bhelgaas-glaptop.roam.corp.google.com> <20171006222428.12211.3635.stgit@bhelgaas-glaptop.roam.corp.google.com> <20171012140548.10754506@karo-electronics.de> Message-ID: <4a93e8f1-8b87-ae58-17c8-06b36849dfaf@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 12/10/17 13:05, Lothar Wa?mann wrote: > Hi, > > On Thu, 12 Oct 2017 12:24:10 +0100 Julien Thierry wrote: >> Hi Bjorn, >> >> On 06/10/17 23:24, Bjorn Helgaas wrote: >>> From: Bjorn Helgaas >>> >>> 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 at axtens.net >>> Tested-by: Daniel Axtens # arm64, ppc64-qemu-tcg >>> Signed-off-by: Bjorn Helgaas >>> --- >>> 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? >> > That cannot not happen, though it isn't quite obvious. > 'vgadev' will only be non-NULL, when the vga_list isn't empty and in > that case pdev has been set up in the list_for_each_entry() loop above. > Indeed, it can't be NULL. However, in that case we would be using the pdev from the last vgadev in the list whereas this last case suggest we are picking the first vgadev in the list. So I don't understand why 'pdev' is being used rather than 'vgadev-pdev'. Thanks, -- Julien Thierry