Re: [PATCH v3 4/9] PCI/VGA: Improve the default VGA device selection

From: suijingfeng
Date: Mon Jul 17 2023 - 10:08:58 EST

Hi,


Fixes: f6b1772b2555 ('vgaarb: remove the unused irq_set_state argument to vga_client_register')


Because after applied that patch, there have only one callback mechanism we can use, not two anymore.


On 2023/7/12 00:43, Sui Jingfeng wrote:
From: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>

Currently, the strategy of selecting the default boot on a multiple video
card coexistence system is not perfect. Potential problems are:

1) This function is a no-op on non-x86 architectures.
2) It does not take the PCI Bar may get relocated into consideration.
3) It is not effective for the PCI device without a dedicated VRAM Bar.
4) It is device-agnostic, thus it has to waste the effort to iterate all
of the PCI Bar to find the VRAM aperture.
5) It has invented lots of methods to determine which one is the default
boot device, but this is still a policy because it doesn't give the
user a choice to override.

With the observation that device drivers may have better knowledge about
which PCI bar contains the firmware FB. This patch tries to solve the above
problems by introducing a function callback to the vga_client_register()
function interface. DRM device drivers for the PCI device could provide
a xx_vga_is_primary_gpu() function callback during the driver loading time.
Once the driver binds the device successfully, VRAARB will call back to
the driver. This gives the device drivers a chance to provide accurate
boot device identification. Which in turn unlock the abitration service
to non-x86 architectures. A device driver can also just pass a NULL pointer
to keep the original behavior.

This patch is intended to introducing the mechanism only, the specific
implementation is left to the authors of various device driver. Also honor
the comment: "Clients have *TWO* callback mechanisms they can use"

Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Christian Konig <christian.koenig@xxxxxxx>
Cc: Pan Xinhui <Xinhui.Pan@xxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
Cc: Karol Herbst <kherbst@xxxxxxxxxx>
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Hawking Zhang <Hawking.Zhang@xxxxxxx>
Cc: Mario Limonciello <mario.limonciello@xxxxxxx>
Cc: Lijo Lazar <lijo.lazar@xxxxxxx>
Cc: YiPeng Chai <YiPeng.Chai@xxxxxxx>
Cc: Bokun Zhang <Bokun.Zhang@xxxxxxx>
Cc: Likun Gao <Likun.Gao@xxxxxxx>
Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
Cc: Yishai Hadas <yishaih@xxxxxxxxxx>
Cc: Abhishek Sahu <abhsahu@xxxxxxxxxx>
Cc: Yi Liu <yi.l.liu@xxxxxxxxx>
Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx> # i915
Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx> # nouveau
Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 2 +-
drivers/gpu/drm/i915/display/intel_vga.c | 3 +-
drivers/gpu/drm/loongson/lsdc_drv.c | 2 +-
drivers/gpu/drm/nouveau/nouveau_vga.c | 2 +-
drivers/gpu/drm/radeon/radeon_device.c | 2 +-
drivers/pci/vgaarb.c | 55 ++++++++++++++++++++--
drivers/vfio/pci/vfio_pci_core.c | 2 +-
include/linux/vgaarb.h | 8 ++--
8 files changed, 61 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index a92c6189b4b6..d98f0801ac77 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -4103,7 +4103,7 @@ int amdgpu_device_init(struct amdgpu_device *adev,
/* this will fail for cards that aren't VGA class devices, just
* ignore it */
if ((adev->pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA)
- vga_client_register(adev->pdev, amdgpu_device_vga_set_decode);
+ vga_client_register(adev->pdev, amdgpu_device_vga_set_decode, NULL);
px = amdgpu_device_supports_px(ddev);
diff --git a/drivers/gpu/drm/i915/display/intel_vga.c b/drivers/gpu/drm/i915/display/intel_vga.c
index 286a0bdd28c6..98d7d4dffe9f 100644
--- a/drivers/gpu/drm/i915/display/intel_vga.c
+++ b/drivers/gpu/drm/i915/display/intel_vga.c
@@ -115,7 +115,6 @@ intel_vga_set_decode(struct pci_dev *pdev, bool enable_decode)
int intel_vga_register(struct drm_i915_private *i915)
{
-
struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
int ret;
@@ -127,7 +126,7 @@ int intel_vga_register(struct drm_i915_private *i915)
* then we do not take part in VGA arbitration and the
* vga_client_register() fails with -ENODEV.
*/
- ret = vga_client_register(pdev, intel_vga_set_decode);
+ ret = vga_client_register(pdev, intel_vga_set_decode, NULL);
if (ret && ret != -ENODEV)
return ret;
diff --git a/drivers/gpu/drm/loongson/lsdc_drv.c b/drivers/gpu/drm/loongson/lsdc_drv.c
index 188ec82afcfb..d10a28c2c494 100644
--- a/drivers/gpu/drm/loongson/lsdc_drv.c
+++ b/drivers/gpu/drm/loongson/lsdc_drv.c
@@ -289,7 +289,7 @@ static int lsdc_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
pci_set_drvdata(pdev, ddev);
- vga_client_register(pdev, lsdc_vga_set_decode);
+ vga_client_register(pdev, lsdc_vga_set_decode, NULL);
drm_kms_helper_poll_init(ddev);
diff --git a/drivers/gpu/drm/nouveau/nouveau_vga.c b/drivers/gpu/drm/nouveau/nouveau_vga.c
index f8bf0ec26844..162b4f4676c7 100644
--- a/drivers/gpu/drm/nouveau/nouveau_vga.c
+++ b/drivers/gpu/drm/nouveau/nouveau_vga.c
@@ -92,7 +92,7 @@ nouveau_vga_init(struct nouveau_drm *drm)
return;
pdev = to_pci_dev(dev->dev);
- vga_client_register(pdev, nouveau_vga_set_decode);
+ vga_client_register(pdev, nouveau_vga_set_decode, NULL);
/* don't register Thunderbolt eGPU with vga_switcheroo */
if (pci_is_thunderbolt_attached(pdev))
diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
index afbb3a80c0c6..71f2ff39d6a1 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -1425,7 +1425,7 @@ int radeon_device_init(struct radeon_device *rdev,
/* if we have > 1 VGA cards, then disable the radeon VGA resources */
/* this will fail for cards that aren't VGA class devices, just
* ignore it */
- vga_client_register(rdev->pdev, radeon_vga_set_decode);
+ vga_client_register(rdev->pdev, radeon_vga_set_decode, NULL);
if (rdev->flags & RADEON_IS_PX)
runtime = true;
diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index 953daf731b2c..610ddcccef24 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -53,6 +53,7 @@ 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_primary_gpu)(struct pci_dev *pdev);
};
static LIST_HEAD(vga_list);
@@ -958,6 +959,13 @@ EXPORT_SYMBOL(vga_set_legacy_decoding);
* @set_decode callback: If a client can disable its GPU VGA resource, it
* will get a callback from this to set the encode/decode state.
*
+ * @is_primary_gpu callback: call back to the device driver, query if a PCI
+ * GPU client is the primary display device, as device drivers (drm-based
+ * or fbdev-based) may have better knowledge if a specific device is the
+ * default boot device or should be the default boot device. But this
+ * callback is optional. A device driver can simply pass a NULL pointer to
+ * adhere to the original rules of arbitration.
+ *
* Rationale: we cannot disable VGA decode resources unconditionally, some
* single GPU laptops seem to require ACPI or BIOS access to the VGA registers
* to control things like backlights etc. Hopefully newer multi-GPU laptops do
@@ -973,7 +981,8 @@ EXPORT_SYMBOL(vga_set_legacy_decoding);
* Returns: 0 on success, -1 on failure
*/
int vga_client_register(struct pci_dev *pdev,
- unsigned int (*set_decode)(struct pci_dev *pdev, bool decode))
+ unsigned int (*set_decode)(struct pci_dev *pdev, bool decode),
+ bool (*is_primary_gpu)(struct pci_dev *pdev))
{
int ret = -ENODEV;
struct vga_device *vgadev;
@@ -985,6 +994,7 @@ int vga_client_register(struct pci_dev *pdev,
goto bail;
vgadev->set_decode = set_decode;
+ vgadev->is_primary_gpu = is_primary_gpu;
ret = 0;
bail:
@@ -1490,6 +1500,30 @@ static void vga_arbiter_notify_clients(void)
spin_unlock_irqrestore(&vga_lock, flags);
}
+static void vga_arbiter_do_arbitration(struct pci_dev *pdev)
+{
+ struct vga_device *vgadev;
+ unsigned long flags;
+
+ spin_lock_irqsave(&vga_lock, flags);
+ list_for_each_entry(vgadev, &vga_list, list) {
+ if (vgadev->pdev != pdev)
+ continue;
+
+ /* This device already the boot device, do nothing */
+ if (pdev == vga_default_device())
+ break;
+
+ if (vgadev->is_primary_gpu) {
+ if (vgadev->is_primary_gpu(pdev)) {
+ vgaarb_info(&pdev->dev, "Overriding as primary GPU\n");
+ vga_set_default_device(pdev);
+ }
+ }
+ }
+ spin_unlock_irqrestore(&vga_lock, flags);
+}
+
static int pci_notify(struct notifier_block *nb, unsigned long action,
void *data)
{
@@ -1509,13 +1543,24 @@ static int pci_notify(struct notifier_block *nb, unsigned long action,
* cases of hotplugable vga cards.
*/
- if (action == BUS_NOTIFY_ADD_DEVICE)
+ switch (action) {
+ case BUS_NOTIFY_ADD_DEVICE:
notify = vga_arbiter_add_pci_device(pdev);
- else if (action == BUS_NOTIFY_DEL_DEVICE)
+ if (notify)
+ vga_arbiter_notify_clients();
+ break;
+ case BUS_NOTIFY_DEL_DEVICE:
notify = vga_arbiter_del_pci_device(pdev);
+ if (notify)
+ vga_arbiter_notify_clients();
+ break;
+ case BUS_NOTIFY_BOUND_DRIVER:
+ vga_arbiter_do_arbitration(pdev);
+ break;
+ default:
+ break;
+ }
- if (notify)
- vga_arbiter_notify_clients();
return 0;
}
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 20d7b69ea6ff..531c4d8ef26e 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -2108,7 +2108,7 @@ static int vfio_pci_vga_init(struct vfio_pci_core_device *vdev)
if (ret)
return ret;
- ret = vga_client_register(pdev, vfio_pci_set_decode);
+ ret = vga_client_register(pdev, vfio_pci_set_decode, NULL);
if (ret)
return ret;
vga_set_legacy_decoding(pdev, vfio_pci_set_decode(pdev, false));
diff --git a/include/linux/vgaarb.h b/include/linux/vgaarb.h
index 97129a1bbb7d..e4102be21f47 100644
--- a/include/linux/vgaarb.h
+++ b/include/linux/vgaarb.h
@@ -33,7 +33,8 @@ struct pci_dev *vga_default_device(void);
void vga_set_default_device(struct pci_dev *pdev);
int vga_remove_vgacon(struct pci_dev *pdev);
int vga_client_register(struct pci_dev *pdev,
- unsigned int (*set_decode)(struct pci_dev *pdev, bool state));
+ unsigned int (*set_decode)(struct pci_dev *pdev, bool state),
+ bool (*is_primary_gpu)(struct pci_dev *pdev));
#else /* CONFIG_VGA_ARB */
static inline void vga_set_legacy_decoding(struct pci_dev *pdev,
unsigned int decodes)
@@ -59,7 +60,8 @@ static inline int vga_remove_vgacon(struct pci_dev *pdev)
return 0;
}
static inline int vga_client_register(struct pci_dev *pdev,
- unsigned int (*set_decode)(struct pci_dev *pdev, bool state))
+ unsigned int (*set_decode)(struct pci_dev *pdev, bool state),
+ bool (*is_primary_gpu)(struct pci_dev *pdev))
{
return 0;
}
@@ -97,7 +99,7 @@ static inline int vga_get_uninterruptible(struct pci_dev *pdev,
static inline void vga_client_unregister(struct pci_dev *pdev)
{
- vga_client_register(pdev, NULL);
+ vga_client_register(pdev, NULL, NULL);
}
#endif /* LINUX_VGA_H */