[PATCH] vgaarb: Rework default VGA device selection
Bjorn Helgaas
helgaas at kernel.org
Tue Jul 20 22:19:23 UTC 2021
On Mon, Jul 05, 2021 at 06:05:03PM +0800, Huacai Chen wrote:
> Currently, vga_arb_device_init() selects the first probed VGA device
> with VGA legacy resources enabled as the default device. However, some
> BMC-based VGA cards (e.g., AST2500 and HiSilicon D05) don't enable VGA
> legacy resources because their built-in upstream bridges don't support
> PCI_BRIDGE_CTL_VGA. This makes "no default VGA card" and breaks X.org
> auto-detection.
>
> Commit a37c0f48950b56f6ef2e ("vgaarb: Select a default VGA device even
> if there's no legacy VGA") try to solve this problem but fails on some
> platforms, because it relies on the initcall order:
>
> We should call vga_arb_device_init() after PCI enumeration, otherwise it
> may fail to select the default VGA device. Since vga_arb_device_init()
> and PCI enumeration function (i.e., pcibios_init() or acpi_init()) are
> both wrapped by subsys_initcall(), their sequence is not assured. So, it
> is possible to use subsys_initcall_sync() instead of subsys_initcall()
> to wrap vga_arb_device_init().
>
> However, the above approach still has drawbacks, it cannot handle the
> cases that a VGA card is hot-plugged, or the gpu driver is compiled as a
> module.
>
> So, as suggested by Bjorn Helgaas, this patch rework the selection:
> 1, Remove direct vga_arb_select_default_device() calls in vga_arb_
> device_init().
> 2, Rename vga_arb_select_default_device() to vga_arb_update_default_
> device(), which selects the first probed VGA device as the default
> (whether legacy resources enabled or not), and update the default
> device if a better one is found (device with legacy resources enabled
> is better, device owns the firmware framebuffer is even better).
> 3, Every time a new VGA device is probed, vga_arbiter_add_pci_device()
> is called, and vga_arb_update_default_device() is also called. So the
> hotplug case and the module case can also be handled.
>
> Signed-off-by: Huacai Chen <chenhuacai at loongson.cn>
> ---
> drivers/gpu/vga/vgaarb.c | 219 +++++++++++++++++----------------------
> 1 file changed, 97 insertions(+), 122 deletions(-)
I think maybe it *would* be a good idea to move this to drivers/pci,
and I think it would be nice to make the move the very first patch in
a series because I think there may be follow-ons, and it would be nice
to get more of the history in the new location after the break.
For example, if it's in drivers/pci, we can call the arbiter directly
from the enumeration/removal code instead of using a bus notifier.
I put this on a branch so you can see what it looks like:
https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/log/?h=review/vga
I tried to pull out as much stuff as I could into smaller patches so
this one is a little bit more understandable.
But we definitely need some work on the commit log. The first three
paragraphs seem to describe the approach you *didn't* use. We don't
need that.
But we *do* need an explanation of why we need this patch and how it
works. Based on the patch, I assume the initcall ordering is
different on your system, which exposes a problem in
vga_arbiter_add_pci_device():
Looking at [1], I think that on your system, vga_arb_device_init()
runs before the VGA card is enumerated, so it doesn't set the card as
the default VGA device.
We do call vga_arbiter_add_pci_device() when we enumerate the device,
but it doesn't set the card as the default device either because the
bridge upstream from it doesn't support PCI_BRIDGE_CTL_VGA.
So the commit log needs to (1) explain why your initcall ordering is
unusual, and (2) explain the approach, which IIUC is basically to add
the vga_arb_select_default_device() functionality to
vga_arbiter_add_pci_device().
[1] https://lore.kernel.org/linux-pci/20210518193100.GA148462@bjorn-Precision-5520/
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index 949fde433ea2..07770aae3aaf 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -586,6 +586,97 @@ void vga_put(struct pci_dev *pdev, unsigned int rsrc)
> }
> EXPORT_SYMBOL(vga_put);
>
> +#if defined(CONFIG_ACPI)
> +static bool vga_arb_integrated_gpu(struct device *dev)
> +{
> + struct acpi_device *adev = ACPI_COMPANION(dev);
> +
> + return adev && !strcmp(acpi_device_hid(adev), ACPI_VIDEO_HID);
> +}
> +#else
> +static bool vga_arb_integrated_gpu(struct device *dev)
> +{
> + return false;
> +}
> +#endif
> +
> +static void vga_arb_update_default_device(struct vga_device *vgadev)
> +{
> + struct pci_dev *pdev = vgadev->pdev;
> + struct device *dev = &pdev->dev;
> + struct vga_device *vgadev_default;
> +#if defined(CONFIG_X86) || defined(CONFIG_IA64)
> + int i;
> + unsigned long flags;
> + u64 base = screen_info.lfb_base;
> + u64 size = screen_info.lfb_size;
> + u64 limit;
> + resource_size_t start, end;
> +#endif
> +
> + /* Deal with VGA default device. Use first enabled one
> + * by default if arch doesn't have it's own hook
> + */
> + if (!vga_default_device()) {
> + if ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)
> + vgaarb_info(dev, "setting as boot VGA device\n");
> + else
> + vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
> + vga_set_default_device(pdev);
> + }
> +
> + vgadev_default = vgadev_find(vga_default);
> +
> + /* Overridden by a better device */
> + if (vgadev_default && ((vgadev_default->owns & VGA_RSRC_LEGACY_MASK) == 0)
> + && ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
> + vgaarb_info(dev, "overriding boot VGA device\n");
> + vga_set_default_device(pdev);
> + }
> +
> + if (vga_arb_integrated_gpu(dev)) {
> + vgaarb_info(dev, "overriding boot VGA device\n");
> + vga_set_default_device(pdev);
> + }
> +
> +#if defined(CONFIG_X86) || defined(CONFIG_IA64)
> + if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
> + base |= (u64)screen_info.ext_lfb_base << 32;
> +
> + limit = base + size;
> +
> + /*
> + * Override vga_arbiter_add_pci_device()'s I/O based detection
> + * as it may take the wrong device (e.g. on Apple system under
> + * EFI).
> + *
> + * Select the device owning the boot framebuffer if there is
> + * one.
> + */
> +
> + /* Does firmware framebuffer belong to us? */
> + for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
> + flags = pci_resource_flags(vgadev->pdev, i);
> +
> + if ((flags & IORESOURCE_MEM) == 0)
> + continue;
> +
> + start = pci_resource_start(vgadev->pdev, i);
> + end = pci_resource_end(vgadev->pdev, i);
> +
> + if (!start || !end)
> + continue;
> +
> + if (base < start || limit >= end)
> + continue;
> +
> + if (vgadev->pdev != vga_default_device())
> + vgaarb_info(dev, "overriding boot device\n");
> + vga_set_default_device(vgadev->pdev);
> + }
> +#endif
> +}
> +
> /*
> * Rules for using a bridge to control a VGA descendant decoding: if a bridge
> * has only one VGA descendant then it can be used to control the VGA routing
> @@ -643,6 +734,11 @@ static void vga_arbiter_check_bridge_sharing(struct vga_device *vgadev)
> }
> new_bus = new_bus->parent;
> }
> +
> + if (vgadev->bridge_has_one_vga == true)
> + vgaarb_info(&vgadev->pdev->dev, "bridge control possible\n");
> + else
> + vgaarb_info(&vgadev->pdev->dev, "no bridge control possible\n");
> }
>
> /*
> @@ -713,15 +809,7 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
> bus = bus->parent;
> }
>
> - /* Deal with VGA default device. Use first enabled one
> - * by default if arch doesn't have it's own hook
> - */
> - if (vga_default == NULL &&
> - ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
> - vgaarb_info(&pdev->dev, "setting as boot VGA device\n");
> - vga_set_default_device(pdev);
> - }
> -
> + vga_arb_update_default_device(vgadev);
> vga_arbiter_check_bridge_sharing(vgadev);
>
> /* Add to the list */
> @@ -1451,111 +1539,10 @@ static struct miscdevice vga_arb_device = {
> MISC_DYNAMIC_MINOR, "vga_arbiter", &vga_arb_device_fops
> };
>
> -#if defined(CONFIG_ACPI)
> -static bool vga_arb_integrated_gpu(struct device *dev)
> -{
> - struct acpi_device *adev = ACPI_COMPANION(dev);
> -
> - return adev && !strcmp(acpi_device_hid(adev), ACPI_VIDEO_HID);
> -}
> -#else
> -static bool vga_arb_integrated_gpu(struct device *dev)
> -{
> - return false;
> -}
> -#endif
> -
> -static void __init vga_arb_select_default_device(void)
> -{
> - struct pci_dev *pdev, *found = NULL;
> - struct vga_device *vgadev;
> -
> -#if defined(CONFIG_X86) || defined(CONFIG_IA64)
> - u64 base = screen_info.lfb_base;
> - u64 size = screen_info.lfb_size;
> - u64 limit;
> - resource_size_t start, end;
> - unsigned long flags;
> - int i;
> -
> - if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
> - base |= (u64)screen_info.ext_lfb_base << 32;
> -
> - limit = base + size;
> -
> - list_for_each_entry(vgadev, &vga_list, list) {
> - struct device *dev = &vgadev->pdev->dev;
> - /*
> - * Override vga_arbiter_add_pci_device()'s I/O based detection
> - * as it may take the wrong device (e.g. on Apple system under
> - * EFI).
> - *
> - * Select the device owning the boot framebuffer if there is
> - * one.
> - */
> -
> - /* Does firmware framebuffer belong to us? */
> - for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
> - flags = pci_resource_flags(vgadev->pdev, i);
> -
> - if ((flags & IORESOURCE_MEM) == 0)
> - continue;
> -
> - start = pci_resource_start(vgadev->pdev, i);
> - end = pci_resource_end(vgadev->pdev, i);
> -
> - if (!start || !end)
> - continue;
> -
> - if (base < start || limit >= end)
> - continue;
> -
> - if (!vga_default_device())
> - vgaarb_info(dev, "setting as boot device\n");
> - else if (vgadev->pdev != vga_default_device())
> - vgaarb_info(dev, "overriding boot device\n");
> - vga_set_default_device(vgadev->pdev);
> - }
> - }
> -#endif
> -
> - if (!vga_default_device()) {
> - list_for_each_entry_reverse(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)) {
> - found = pdev;
> - if (vga_arb_integrated_gpu(dev))
> - break;
> - }
> - }
> - }
> -
> - if (found) {
> - vgaarb_info(&found->dev, "setting as boot device (VGA legacy resources not available)\n");
> - vga_set_default_device(found);
> - return;
> - }
> -
> - 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(vgadev->pdev);
> - }
> - }
> -}
> -
> static int __init vga_arb_device_init(void)
> {
> int rc;
> struct pci_dev *pdev;
> - struct vga_device *vgadev;
>
> rc = misc_register(&vga_arb_device);
> if (rc < 0)
> @@ -1571,18 +1558,6 @@ static int __init vga_arb_device_init(void)
> PCI_ANY_ID, pdev)) != NULL)
> vga_arbiter_add_pci_device(pdev);
>
> - list_for_each_entry(vgadev, &vga_list, list) {
> - struct device *dev = &vgadev->pdev->dev;
> -
> - if (vgadev->bridge_has_one_vga)
> - vgaarb_info(dev, "bridge control possible\n");
> - else
> - vgaarb_info(dev, "no bridge control possible\n");
> - }
> -
> - vga_arb_select_default_device();
> -
> - pr_info("loaded\n");
> return rc;
> }
> subsys_initcall(vga_arb_device_init);
> --
> 2.27.0
>
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