[+cc linux-pci] On Mon, Jul 04, 2022 at 12:33:50AM -0400, Cal Peake wrote: > My first attempt at solving this problem was based on a bit of a > misunderstanding of the code and, while it worked, could be much improved. Can you outline the problem this solves in the commit log? > This is a new attempt that creates the module parameter 'vgaarb.bootdev' > that can be passed a PCI ID (e.g. 0a:00.0) that the VGA arbiter will > attempt to use as the boot VGA device over any other eligible devices. > > If the passed ID is invalid or is an ineligible device, the arbiter will > fallback to its normal method of trying to find the preferred device for > the job. > > I've tested it thoroughly and it is working very well for me. > > The patch is available below for review and, if found acceptable, can be > pulled via: > > git pull https://github.com/peake/linux.git vgaarb-2 > > -- > Cal Peake > > Signed-off-by: Cal Peake <cp@xxxxxxxxxxxxxxxxxxx> > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 2522b11e593f..21ac87f4a8a9 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -6518,6 +6518,13 @@ > This is actually a boot loader parameter; the value is > passed to the kernel using a special protocol. > > + vgaarb.bootdev= [PCI] Specify the PCI ID (e.g. 0e:00.0) of the > + device to use as the boot VGA device, overriding > + the heuristic used to normally determine which > + of the eligible VGA devices to use. If the device > + specified is not valid or not eligible, then we > + fallback to the heuristic. > + > vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. > May slow down system boot speed, especially when > enabled on systems with a large amount of memory. > diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c > index f80b6ec88dc3..d3689b7dc63d 100644 > --- a/drivers/pci/vgaarb.c > +++ b/drivers/pci/vgaarb.c > @@ -35,6 +35,34 @@ > > #include <linux/vgaarb.h> > > +static char *bootdev __initdata; > +module_param(bootdev, charp, 0); > +MODULE_PARM_DESC(bootdev, "Force boot device to the specified PCI ID"); > + > +/* > + * Initialize to the last possible ID to have things work as normal > + * when no 'bootdev' option is supplied. We especially do not want > + * this to be zero (0) since that is a valid PCI ID (00:00.0). > + */ > +static u16 bootdev_id = 0xffff; > + > +static void __init parse_bootdev(char *input) > +{ > + unsigned int bus, dev, func; > + int ret; > + > + if (input == NULL) > + return; > + > + ret = sscanf(input, "%x:%x.%x", &bus, &dev, &func); > + if (ret != 3) { > + pr_warn("Improperly formatted PCI ID: %s\n", input); > + return; > + } > + > + bootdev_id = PCI_DEVID(bus, PCI_DEVFN(dev, func)); > +} > + > static void vga_arbiter_notify_clients(void); > /* > * We keep a list of all vga devices in the system to speed > @@ -53,6 +81,7 @@ struct vga_device { > bool bridge_has_one_vga; > bool is_firmware_default; /* device selected by firmware */ > unsigned int (*set_decode)(struct pci_dev *pdev, bool decode); > + bool is_chosen_one; /* device specified on command line */ > }; > > static LIST_HEAD(vga_list); > @@ -605,6 +634,7 @@ static bool vga_is_boot_device(struct vga_device *vgadev) > > /* > * We select the default VGA device in this order: > + * User specified device (see module param bootdev=) > * Firmware framebuffer (see vga_arb_select_default_device()) > * Legacy VGA device (owns VGA_RSRC_LEGACY_MASK) > * Non-legacy integrated device (see vga_arb_select_default_device()) > @@ -612,6 +642,14 @@ static bool vga_is_boot_device(struct vga_device *vgadev) > * Other device (see vga_arb_select_default_device()) > */ > > + if (boot_vga && boot_vga->is_chosen_one) > + return false; > + > + if (bootdev_id == PCI_DEVID(pdev->bus->number, pdev->devfn)) { > + vgadev->is_chosen_one = true; > + return true; > + } > + > /* > * We always prefer a firmware default device, so if we've already > * found one, there's no need to consider vgadev. > @@ -1544,6 +1582,8 @@ static int __init vga_arb_device_init(void) > int rc; > struct pci_dev *pdev; > > + parse_bootdev(bootdev); > + > rc = misc_register(&vga_arb_device); > if (rc < 0) > pr_err("error %d registering device\n", rc);
