<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> </head> <body> Hi, <div class="moz-cite-prefix">On 2023/7/17 17:51, suijingfeng wrote: </div> <blockquote type="cite" cite="mid:6b4ff3d5-293e-7bf3-f5df-babc14661c44@loongson.cn"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> Hi, <div class="moz-cite-prefix">On 2023/7/11 21:43, Sui Jingfeng wrote: </div> <blockquote type="cite" cite="mid:20230711134354.755966-3-sui.jingfeng@linux.dev"> <pre class="moz-quote-pre" wrap="">From: Sui Jingfeng <a class="moz-txt-link-rfc2396E" href="mailto:suijingfeng@loongson.cn" moz-do-not-send="true"><suijingfeng@loongson.cn></a> Currently, vgaarb only cares about PCI VGA-compatible class devices. While vga_arbiter_del_pci_device() gets called unbalanced when some PCI device is about to be removed. This happens even during the boot process. Another reason is that the vga_arb_device_init() function is not efficient. Since we only care about VGA-compatible devices (pdev->class == 0x030000), We could filter the unqualified devices out in the vga_arb_device_init() function. While the current implementation is to search all PCI devices in a system, this is not necessary. Reviewed-by: Mario Limonciello <a class="moz-txt-link-rfc2396E" href="mailto:mario.limonciello@amd.com" moz-do-not-send="true"><mario.limonciello@amd.com></a> Signed-off-by: Sui Jingfeng <a class="moz-txt-link-rfc2396E" href="mailto:suijingfeng@loongson.cn" moz-do-not-send="true"><suijingfeng@loongson.cn></a> --- drivers/pci/vgaarb.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c index c1bc6c983932..021116ed61cb 100644 --- a/drivers/pci/vgaarb.c +++ b/drivers/pci/vgaarb.c @@ -754,10 +754,6 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev) struct pci_dev *bridge; u16 cmd; - /* Only deal with VGA class devices */ - if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA) - return false; - /* Allocate structure */ vgadev = kzalloc(sizeof(struct vga_device), GFP_KERNEL); if (vgadev == NULL) { @@ -1502,6 +1498,10 @@ static int pci_notify(struct notifier_block *nb, unsigned long action, vgaarb_dbg(dev, "%s\n", __func__); + /* Deal with VGA compatible devices only */ + if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA) + return 0; + /* For now we're only intereted in devices added and removed. I didn't * test this thing here, so someone needs to double check for the * cases of hotplugable vga cards. */ @@ -1534,8 +1534,8 @@ static struct miscdevice vga_arb_device = { static int __init vga_arb_device_init(void) { + struct pci_dev *pdev = NULL; int rc; - struct pci_dev *pdev; rc = misc_register(&vga_arb_device); if (rc < 0) @@ -1543,13 +1543,14 @@ static int __init vga_arb_device_init(void) bus_register_notifier(&pci_bus_type, &pci_notifier); - /* We add all PCI devices satisfying VGA class in the arbiter by - * default */ - pdev = NULL; - while ((pdev = - pci_get_subsys(PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID, - PCI_ANY_ID, pdev)) != NULL) - vga_arbiter_add_pci_device(pdev); + /* + * We add all PCI VGA compatible devices in the arbiter by default + */ + do { + pdev = pci_get_class(PCI_CLASS_DISPLAY_VGA << 8, pdev); + if (pdev) + vga_arbiter_add_pci_device(pdev); + } while (pdev); </pre> </blockquote> <pre id="b">I suddenly remember one more thing that I forget to explain. In a previous thread[1] of previous version of this series, Maciej seems argue that PCI_CLASS_NOT_DEFINED_VGA should be handled also. But, even I try to handled PCI_CLASS_NOT_DEFINED_VGA at here, this card still will not be annotate as boot_vga, because the pci_dev_attrs_are_visible() function only consider VGA compatible devices which (pdev->class >> 8 == PCI_CLASS_DISPLAY_VGA) is true. See [2]. Intel integrated GPU is more intelligent, which could change their class of the PCI(e) device to 0x038000 when multiple GPU co-exist. Even though the GPU can display. This is configurable by the firmware, but this is trying to escape the arbitration by changing is PCI id. </pre> </blockquote> <pre id="b">"by changing is PCI id" -> "by changing its PCI(e) class number". For example, the intel GPU will change their PCI class number from 0x030000 to 0x038000, if a user choose the dGPU as primary by setting their UEFI firmware from the BIOS. But other GPUs may not support to change their PCI class number. </pre> <blockquote type="cite" cite="mid:6b4ff3d5-293e-7bf3-f5df-babc14661c44@loongson.cn"> <pre id="b"> So, PCI devices belong to the PCI_CLASS_DISPLAY_OTHER, PCI_CLASS_DISPLAY_3D and PCI_CLASS_DISPLAY_XGA can not participate in the arbitration. They are all will be get filtered. </pre> </blockquote> I means that PCI devices with their PCI class number equal to PCI_CLASS_DISPLAY_OTHER, PCI_CLASS_DISPLAY_3D and PCI_CLASS_DISPLAY_XGA will get ignored by vgaarb currently. Even we throw other devices(DISPLAY_OTHER, DISPLAY_3D, DISPLAY_XGA) into the arbitrator, We still not make a meaningful progress, I need also to change the code in link [2] to make the boot_vga visible to userspace. Because X server is the end consumer. This already form an ABI. So change the code here alone is not enough to expand vgaarb. <blockquote type="cite" cite="mid:6b4ff3d5-293e-7bf3-f5df-babc14661c44@loongson.cn"> <pre id="b"> So, this is a limitation of the vgaarb itself. While I could help to improve it in the future, what do you think?</pre> </blockquote> <blockquote type="cite" cite="mid:6b4ff3d5-293e-7bf3-f5df-babc14661c44@loongson.cn"> <pre id="b"> Is my express clear? </pre> </blockquote> Am I express my thoughts clearly ? <blockquote type="cite" cite="mid:6b4ff3d5-293e-7bf3-f5df-babc14661c44@loongson.cn"> <pre id="b"> </pre> [1] <a class="moz-txt-link-freetext" href="https://lkml.kernel.org/nouveau/alpine.DEB.2.21.2306190339590.14084@angie.orcam.me.uk/#t" moz-do-not-send="true">https://lkml.kernel.org/nouveau/alpine.DEB.2.21.2306190339590.14084@angie.orcam.me.uk/#t</a> [2] <a class="moz-txt-link-freetext" href="https://elixir.bootlin.com/linux/latest/source/drivers/pci/pci-sysfs.c#L1544" moz-do-not-send="true">https://elixir.bootlin.com/linux/latest/source/drivers/pci/pci-sysfs.c#L1544</a> </blockquote> <pre id="b"> Alex acclaims that "we won't need vgaarb if the platform has no VGA devices", see [3]. while this is not 100% correct, because X server is the primary consumer of the boot_vga flag, the convention usage of the userspace and the kernel space is already established. So without we can craft something new easily without significant change. [3] <a class="moz-txt-link-freetext" href="https://lkml.kernel.org/nouveau/CADnq5_PFoM2O8mCd6+VFfu9Nc-Hg_HTnwEMxrq0FGRpva1kKiA@mail.gmail.com/">https://lkml.kernel.org/nouveau/CADnq5_PFoM2O8mCd6+VFfu9Nc-Hg_HTnwEMxrq0FGRpva1kKiA@mail.gmail.com/</a> </pre> <blockquote type="cite" cite="mid:6b4ff3d5-293e-7bf3-f5df-babc14661c44@loongson.cn"> <blockquote type="cite" cite="mid:20230711134354.755966-3-sui.jingfeng@linux.dev"> <pre class="moz-quote-pre" wrap=""> pr_info("loaded\n"); return rc; </pre> </blockquote> </blockquote> </body> </html>