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Tue, 17 Jun 2025 12:22:32 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGvT+wWOgl7pfKZbTZ4DvfyUSmBDBBx9AlWceV4usmHGm1/hFR2YB75bZK6jJl5rI9kUZOEVg== X-Received: by 2002:a05:6602:6d01:b0:85b:544c:ba6c with SMTP id ca18e2360f4ac-875ded03081mr426799139f.1.1750188152172; Tue, 17 Jun 2025 12:22:32 -0700 (PDT) Received: from redhat.com ([38.15.36.11]) by smtp.gmail.com with ESMTPSA id 8926c6da1cb9f-50149b9e03fsm2396367173.52.2025.06.17.12.22.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Jun 2025 12:22:30 -0700 (PDT) Date: Tue, 17 Jun 2025 13:22:28 -0600 From: Alex Williamson To: Mario Limonciello Cc: Bjorn Helgaas , Alex Deucher , Christian =?UTF-8?B?S8O2bmln?= , David Airlie , Simona Vetter , Lukas Wunner , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Woodhouse , Lu Baolu , Joerg Roedel , Will Deacon , Robin Murphy , Jaroslav Kysela , Takashi Iwai , dri-devel@lists.freedesktop.org (open list:DRM DRIVERS), linux-kernel@vger.kernel.org (open list), iommu@lists.linux.dev (open list:INTEL IOMMU (VT-d)), linux-pci@vger.kernel.org (open list:PCI SUBSYSTEM), kvm@vger.kernel.org (open list:VFIO DRIVER), linux-sound@vger.kernel.org (open list:SOUND), Daniel Dadap , Mario Limonciello Subject: Re: [PATCH v2 6/6] vgaarb: Look at all PCI display devices in VGA arbiter Message-ID: <20250617132228.434adebf.alex.williamson@redhat.com> In-Reply-To: <20250617175910.1640546-7-superm1@kernel.org> References: <20250617175910.1640546-1-superm1@kernel.org> <20250617175910.1640546-7-superm1@kernel.org> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.43; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 17 Jun 2025 12:59:10 -0500 Mario Limonciello wrote: > From: Mario Limonciello > > On a mobile system with an AMD integrated GPU + NVIDIA discrete GPU the > AMD GPU is not being selected by some desktop environments for any > rendering tasks. This is because neither GPU is being treated as > "boot_vga" but that is what some environments use to select a GPU [1]. > > The VGA arbiter driver only looks at devices that report as PCI display > VGA class devices. Neither GPU on the system is a PCI display VGA class > device: > > c5:00.0 3D controller: NVIDIA Corporation Device 2db9 (rev a1) > c6:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Device 150e (rev d1) > > If the GPUs were looked at the vga_is_firmware_default() function actually > does do a good job at recognizing the case from the device used for the > firmware framebuffer. > > Modify the VGA arbiter code and matching sysfs file entries to examine all > PCI display class devices. The existing logic stays the same. > > This will cause all GPUs to gain a `boot_vga` file, but the correct device > (AMD GPU in this case) will now show `1` and the incorrect device shows `0`. > Userspace then picks the right device as well. > > Link: https://github.com/robherring/libpciaccess/commit/b2838fb61c3542f107014b285cbda097acae1e12 [1] > Suggested-by: Daniel Dadap > Acked-by: Thomas Zimmermann > Signed-off-by: Mario Limonciello > --- > drivers/pci/pci-sysfs.c | 2 +- > drivers/pci/vgaarb.c | 8 ++++---- > 2 files changed, 5 insertions(+), 5 deletions(-) > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > index 268c69daa4d57..c314ee1b3f9ac 100644 > --- a/drivers/pci/pci-sysfs.c > +++ b/drivers/pci/pci-sysfs.c > @@ -1707,7 +1707,7 @@ static umode_t pci_dev_attrs_are_visible(struct kobject *kobj, > struct device *dev = kobj_to_dev(kobj); > struct pci_dev *pdev = to_pci_dev(dev); > > - if (a == &dev_attr_boot_vga.attr && pci_is_vga(pdev)) > + if (a == &dev_attr_boot_vga.attr && pci_is_display(pdev)) > return a->mode; > > return 0; > diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c > index 78748e8d2dbae..63216e5787d73 100644 > --- a/drivers/pci/vgaarb.c > +++ b/drivers/pci/vgaarb.c > @@ -1499,8 +1499,8 @@ static int pci_notify(struct notifier_block *nb, unsigned long action, > > vgaarb_dbg(dev, "%s\n", __func__); > > - /* Only deal with VGA class devices */ > - if (!pci_is_vga(pdev)) > + /* Only deal with PCI display class devices */ > + if (!pci_is_display(pdev)) > return 0; > > /* > @@ -1546,12 +1546,12 @@ static int __init vga_arb_device_init(void) > > bus_register_notifier(&pci_bus_type, &pci_notifier); > > - /* Add all VGA class PCI devices by default */ > + /* Add all PCI display class devices by default */ > pdev = NULL; > while ((pdev = > pci_get_subsys(PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID, > PCI_ANY_ID, pdev)) != NULL) { > - if (pci_is_vga(pdev)) > + if (pci_is_display(pdev)) > vga_arbiter_add_pci_device(pdev); > } > At the very least a non-VGA device should not mark that it decodes legacy resources, marking the boot VGA device is only a part of what the VGA arbiter does. It seems none of the actual VGA arbitration interfaces have been considered here though. I still think this is a bad idea and I'm not sure Thomas didn't withdraw his ack in the previous round[1]. Thanks, Alex [1]https://lore.kernel.org/all/bc0a3ac2-c86c-43b8-b83f-edfdfa5ee184@suse.de/