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Message-ID: <fa3bfed9-8a6f-4001-bd4a-d4d237b001d3@kernel.org>
Date: Fri, 20 Jun 2025 17:17:44 -0500
From: Mario Limonciello <superm1@...nel.org>
To: Thomas Zimmermann <tzimmermann@...e.de>,
Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Alex Deucher <alexander.deucher@....com>,
Christian König <christian.koenig@....com>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Lukas Wunner <lukas@...ner.de>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, David Woodhouse <dwmw2@...radead.org>,
Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
Alex Williamson <alex.williamson@...hat.com>,
Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
"open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
open list <linux-kernel@...r.kernel.org>,
"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux.dev>,
"open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
"open list:VFIO DRIVER" <kvm@...r.kernel.org>,
"open list:SOUND" <linux-sound@...r.kernel.org>,
Daniel Dadap <ddadap@...dia.com>,
Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v3 6/7] PCI/VGA: Move check for firmware default out of
VGA arbiter
On 6/20/2025 3:45 AM, Thomas Zimmermann wrote:
> Hi
>
> Am 20.06.25 um 04:49 schrieb Mario Limonciello:
>> From: Mario Limonciello <mario.limonciello@....com>
>>
>> The x86 specific check for whether a framebuffer belongs to a device
>> works for display devices as well as VGA devices. Callers to
>> video_is_primary_device() can benefit from checking non-VGA display
>> devices.
>>
>> Move the x86 specific check into x86 specific code, and adjust VGA
>> arbiter to call that code as well. This allows fbcon to find the
>> right PCI device on systems that don't have VGA devices.
>>
>> Suggested-by: Thomas Zimmermann <tzimmermann@...e.de>
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>> arch/x86/video/video-common.c | 28 +++++++++++++++++++++++++++
>> drivers/pci/vgaarb.c | 36 ++---------------------------------
>> 2 files changed, 30 insertions(+), 34 deletions(-)
>>
>> diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-
>> common.c
>> index 81fc97a2a837a..718116e35e450 100644
>> --- a/arch/x86/video/video-common.c
>> +++ b/arch/x86/video/video-common.c
>> @@ -9,6 +9,7 @@
>> #include <linux/module.h>
>> #include <linux/pci.h>
>> +#include <linux/screen_info.h>
>> #include <linux/vgaarb.h>
>> #include <asm/video.h>
>> @@ -27,13 +28,40 @@ EXPORT_SYMBOL(pgprot_framebuffer);
>> bool video_is_primary_device(struct device *dev)
>
> I'm not sure I understand this patch. video_is_primary_device() already
> exists for 3 architectures, including x86. [1] Adding it here should
> produce an error. (?)
I wasn't adding a new implementation of it, I was augmenting the x86
implementation.
But I guess based on your below point it just needs to call
screen_info_pci_dev().
>
> [1] https://elixir.bootlin.com/linux/v6.15.2/A/ident/
> video_is_primary_device
>
> The code on x86 is
>
> bool <https://elixir.bootlin.com/linux/v6.15.2/C/ident/
> bool>video_is_primary_device <https://elixir.bootlin.com/linux/v6.15.2/
> C/ident/video_is_primary_device>(structdevice <https://
> elixir.bootlin.com/linux/v6.15.2/C/ident/device>*dev) { structpci_dev
> <https://elixir.bootlin.com/linux/v6.15.2/C/ident/pci_dev>*pdev; if(!
> dev_is_pci <https://elixir.bootlin.com/linux/v6.15.2/C/ident/
> dev_is_pci>(dev)) returnfalse <https://elixir.bootlin.com/linux/v6.15.2/
> C/ident/false>; pdev=to_pci_dev <https://elixir.bootlin.com/linux/
> v6.15.2/C/ident/to_pci_dev>(dev); return(pdev==vga_default_device
> <https://elixir.bootlin.com/linux/v6.15.2/C/ident/vga_default_device>()); }
>
> I was thinking about extending it to test for additional properties,
> like this
>
> bool <https://elixir.bootlin.com/linux/v6.15.2/C/ident/
> bool>video_is_primary_device <https://elixir.bootlin.com/linux/v6.15.2/
> C/ident/video_is_primary_device>(structdevice <https://
> elixir.bootlin.com/linux/v6.15.2/C/ident/device>*dev) { structpci_dev
> <https://elixir.bootlin.com/linux/v6.15.2/C/ident/pci_dev>*pdev; if(!
> dev_is_pci <https://elixir.bootlin.com/linux/v6.15.2/C/ident/
> dev_is_pci>(dev)) returnfalse <https://elixir.bootlin.com/linux/v6.15.2/
> C/ident/false>; pdev=to_pci_dev <https://elixir.bootlin.com/linux/
> v6.15.2/C/ident/to_pci_dev>(dev); if(pdev==vga_default_device <https://
> elixir.bootlin.com/linux/v6.15.2/C/ident/vga_default_device>()) return
> true for_each_pci_dev() { // test if display and could be primary. }
> return false; // nothing found }
>
The above looks like some bad copy / paste. Could you clarify?
>
> This would then be called from per-device sysfs code that export a
> property similar to boot_vga (such as boot_display).
Here's the other idea I had in mind.
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 268c69daa4d57..8535950b4c0f3 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -30,6 +30,7 @@
#include <linux/msi.h>
#include <linux/of.h>
#include <linux/aperture.h>
+#include <asm/video.h>
#include "pci.h"
#ifndef ARCH_PCI_DEV_GROUPS
@@ -679,6 +680,13 @@ const struct attribute_group *pcibus_groups[] = {
NULL,
};
+static ssize_t boot_console_show(struct device *dev, struct
device_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%u\n", video_is_primary_device(dev));
+}
+static DEVICE_ATTR_RO(boot_console);
+
static ssize_t boot_vga_show(struct device *dev, struct
device_attribute *attr,
char *buf)
{
@@ -1698,6 +1706,7 @@ late_initcall(pci_sysfs_init);
static struct attribute *pci_dev_dev_attrs[] = {
&dev_attr_boot_vga.attr,
+ &dev_attr_boot_console.attr,
NULL,
};
@@ -1710,6 +1719,9 @@ static umode_t pci_dev_attrs_are_visible(struct
kobject *kobj,
if (a == &dev_attr_boot_vga.attr && pci_is_vga(pdev))
return a->mode;
+ if (a == &dev_attr_boot_console.attr && pci_is_display(pdev))
+ return a->mode;
+
return 0;
}
>
>
> The issue is currently just an x86 problem, but I can imagine something
> similar happening on ARM. There we'd have to go through the DT tree to
> figure out the primary device. That's a problem for a later patch set,
> but we should keep this in mind.
I think that the sysfs file idea above would work for any arch.
>
>> {
>> + u64 base = screen_info.lfb_base;
>> + u64 size = screen_info.lfb_size;
>> struct pci_dev *pdev;
>> + struct resource *r;
>> + u64 limit;
>> if (!dev_is_pci(dev))
>> return false;
>> pdev = to_pci_dev(dev);
>> + if (!pci_is_display(pdev))
>> + return false;
>> +
>> + /* Select the device owning the boot framebuffer if there is one */
>> + if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
>> + base |= (u64)screen_info.ext_lfb_base << 32;
>> +
>> + limit = base + size;
>> +
>> + /* Does firmware framebuffer belong to us? */
>> + pci_dev_for_each_resource(pdev, r) {
>> + if (resource_type(r) != IORESOURCE_MEM)
>> + continue;
>> +
>> + if (!r->start || !r->end)
>> + continue;
>> +
>> + if (base < r->start || limit >= r->end)
>> + continue;
>> +
>> + return true;
>> + }
>> +
>
> You can drop all this code and call screen_info_pci_dev() instead. I
> simply never got to update vgaarb to use it.
👍
>
> [2] https://elixir.bootlin.com/linux/v6.15.2/source/drivers/video/
> screen_info_pci.c#L109
>
>> return (pdev == vga_default_device());
>> }
>> EXPORT_SYMBOL(video_is_primary_device);
>> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
>> index 78748e8d2dbae..15ab58c70b016 100644
>> --- a/drivers/pci/vgaarb.c
>> +++ b/drivers/pci/vgaarb.c
>> @@ -26,12 +26,12 @@
>> #include <linux/poll.h>
>> #include <linux/miscdevice.h>
>> #include <linux/slab.h>
>> -#include <linux/screen_info.h>
>> #include <linux/vt.h>
>> #include <linux/console.h>
>> #include <linux/acpi.h>
>> #include <linux/uaccess.h>
>> #include <linux/vgaarb.h>
>> +#include <asm/video.h>
>> static void vga_arbiter_notify_clients(void);
>> @@ -554,38 +554,6 @@ void vga_put(struct pci_dev *pdev, unsigned int
>> rsrc)
>> }
>> EXPORT_SYMBOL(vga_put);
>> -static bool vga_is_firmware_default(struct pci_dev *pdev)
>> -{
>> -#if defined(CONFIG_X86)
>> - u64 base = screen_info.lfb_base;
>> - u64 size = screen_info.lfb_size;
>> - struct resource *r;
>> - u64 limit;
>> -
>> - /* Select the device owning the boot framebuffer if there is one */
>> -
>> - if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
>> - base |= (u64)screen_info.ext_lfb_base << 32;
>> -
>> - limit = base + size;
>> -
>> - /* Does firmware framebuffer belong to us? */
>> - pci_dev_for_each_resource(pdev, r) {
>> - if (resource_type(r) != IORESOURCE_MEM)
>> - continue;
>> -
>> - if (!r->start || !r->end)
>> - continue;
>> -
>> - if (base < r->start || limit >= r->end)
>> - continue;
>> -
>> - return true;
>> - }
>> -#endif
>> - return false;
>> -}
>> -
>> static bool vga_arb_integrated_gpu(struct device *dev)
>> {
>> #if defined(CONFIG_ACPI)
>> @@ -623,7 +591,7 @@ static bool vga_is_boot_device(struct vga_device
>> *vgadev)
>> if (boot_vga && boot_vga->is_firmware_default)
>> return false;
>> - if (vga_is_firmware_default(pdev)) {
>> + if (video_is_primary_device(&pdev->dev)) {
>
> Maybe not change this because you don't want to end up with non-VGA
> devices here.
👍
>
> Best regards
> Thomas
>
>> vgadev->is_firmware_default = true;
>> return true;
>> }
>
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