[PATCH V4 00/10] PCI/VGA: Rework default VGA device selection

[PATCH V4 00/10] PCI/VGA: Rework default VGA device selection

[Huacai Chen]

My original work is at [1].

Bjorn do some rework and extension in V2. It moves the VGA arbiter to
the PCI subsystem, fixes a few nits, and breaks a few pieces to make
the main patch a little smaller.

V3 rewrite the commit log of the last patch (which is also summarized
by Bjorn).

V4 split the last patch to two steps.

All comments welcome!

[1] https://lore.kernel.org/dri-devel/20210705100503.1120643-1-chenhuacai@loongson.cn/

Bjorn Helgaas (4):
  PCI/VGA: Move vgaarb to drivers/pci
  PCI/VGA: Replace full MIT license text with SPDX identifier
  PCI/VGA: Use unsigned format string to print lock counts
  PCI/VGA: Remove empty vga_arb_device_card_gone()

Huacai Chen (6):
  PCI/VGA: Move vga_arb_integrated_gpu() earlier in file
  PCI/VGA: Prefer vga_default_device()
  PCI/VGA: Split out vga_arb_update_default_device()
  PCI/VGA: Log bridge control messages when adding devices
  PCI/VGA: Rework default VGA device selection (Step 1)
  PCI/VGA: Rework default VGA device selection (Step 2)

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> 
---
 drivers/gpu/vga/Kconfig           |  19 ---
 drivers/gpu/vga/Makefile          |   1 -
 drivers/pci/Kconfig               |  19 +++
 drivers/pci/Makefile              |   1 +
 drivers/{gpu/vga => pci}/vgaarb.c | 269 ++++++++++++------------------
 5 files changed, 126 insertions(+), 183 deletions(-)
 rename drivers/{gpu/vga => pci}/vgaarb.c (90%)
--
2.27.0

[PATCH V4 01/10] PCI/VGA: Move vgaarb to drivers/pci

[Huacai Chen]

From: Bjorn Helgaas <bhelgaas@google.com>

The VGA arbiter is really PCI-specific and doesn't depend on any GPU
things.  Move it to the PCI subsystem.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/gpu/vga/Kconfig           | 19 -------------------
 drivers/gpu/vga/Makefile          |  1 -
 drivers/pci/Kconfig               | 19 +++++++++++++++++++
 drivers/pci/Makefile              |  1 +
 drivers/{gpu/vga => pci}/vgaarb.c |  0
 5 files changed, 20 insertions(+), 20 deletions(-)
 rename drivers/{gpu/vga => pci}/vgaarb.c (100%)

diff --git a/drivers/gpu/vga/Kconfig b/drivers/gpu/vga/Kconfig
index 1ad4c4ef0b5e..eb8b14ab22c3 100644
--- a/drivers/gpu/vga/Kconfig
+++ b/drivers/gpu/vga/Kconfig
@@ -1,23 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
-config VGA_ARB
-	bool "VGA Arbitration" if EXPERT
-	default y
-	depends on (PCI && !S390)
-	help
-	  Some "legacy" VGA devices implemented on PCI typically have the same
-	  hard-decoded addresses as they did on ISA. When multiple PCI devices
-	  are accessed at same time they need some kind of coordination. Please
-	  see Documentation/gpu/vgaarbiter.rst for more details. Select this to
-	  enable VGA arbiter.
-
-config VGA_ARB_MAX_GPUS
-	int "Maximum number of GPUs"
-	default 16
-	depends on VGA_ARB
-	help
-	  Reserves space in the kernel to maintain resource locking for
-	  multiple GPUS.  The overhead for each GPU is very small.
-
 config VGA_SWITCHEROO
 	bool "Laptop Hybrid Graphics - GPU switching support"
 	depends on X86
diff --git a/drivers/gpu/vga/Makefile b/drivers/gpu/vga/Makefile
index e92064442d60..9800620deda3 100644
--- a/drivers/gpu/vga/Makefile
+++ b/drivers/gpu/vga/Makefile
@@ -1,3 +1,2 @@
 # SPDX-License-Identifier: GPL-2.0-only
-obj-$(CONFIG_VGA_ARB)  += vgaarb.o
 obj-$(CONFIG_VGA_SWITCHEROO) += vga_switcheroo.o
diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 0c473d75e625..7c9e56d7b857 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -252,6 +252,25 @@ config PCIE_BUS_PEER2PEER
 
 endchoice
 
+config VGA_ARB
+	bool "VGA Arbitration" if EXPERT
+	default y
+	depends on (PCI && !S390)
+	help
+	  Some "legacy" VGA devices implemented on PCI typically have the same
+	  hard-decoded addresses as they did on ISA. When multiple PCI devices
+	  are accessed at same time they need some kind of coordination. Please
+	  see Documentation/gpu/vgaarbiter.rst for more details. Select this to
+	  enable VGA arbiter.
+
+config VGA_ARB_MAX_GPUS
+	int "Maximum number of GPUs"
+	default 16
+	depends on VGA_ARB
+	help
+	  Reserves space in the kernel to maintain resource locking for
+	  multiple GPUS.  The overhead for each GPU is very small.
+
 source "drivers/pci/hotplug/Kconfig"
 source "drivers/pci/controller/Kconfig"
 source "drivers/pci/endpoint/Kconfig"
diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
index d62c4ac4ae1b..ebe720f69b15 100644
--- a/drivers/pci/Makefile
+++ b/drivers/pci/Makefile
@@ -29,6 +29,7 @@ obj-$(CONFIG_PCI_PF_STUB)	+= pci-pf-stub.o
 obj-$(CONFIG_PCI_ECAM)		+= ecam.o
 obj-$(CONFIG_PCI_P2PDMA)	+= p2pdma.o
 obj-$(CONFIG_XEN_PCIDEV_FRONTEND) += xen-pcifront.o
+obj-$(CONFIG_VGA_ARB)		+= vgaarb.o
 
 # Endpoint library must be initialized before its users
 obj-$(CONFIG_PCI_ENDPOINT)	+= endpoint/
diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/pci/vgaarb.c
similarity index 100%
rename from drivers/gpu/vga/vgaarb.c
rename to drivers/pci/vgaarb.c
-- 
2.27.0

[PATCH V4 02/10] PCI/VGA: Replace full MIT license text with SPDX identifier

[Huacai Chen]

From: Bjorn Helgaas <bhelgaas@google.com>

Per Documentation/process/license-rules.rst, the SPDX MIT identifier is
equivalent to including the entire MIT license text from
LICENSES/preferred/MIT.

Replace the MIT license text with the equivalent SPDX identifier.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 23 +----------------------
 1 file changed, 1 insertion(+), 22 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index 949fde433ea2..61b57abcb014 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -1,32 +1,11 @@
+// SPDX-License-Identifier: MIT
 /*
  * vgaarb.c: Implements the VGA arbitration. For details refer to
  * Documentation/gpu/vgaarbiter.rst
  *
- *
  * (C) Copyright 2005 Benjamin Herrenschmidt <benh@kernel.crashing.org>
  * (C) Copyright 2007 Paulo R. Zanoni <przanoni@gmail.com>
  * (C) Copyright 2007, 2009 Tiago Vignatti <vignatti@freedesktop.org>
- *
- * Permission is hereby granted, free of charge, to any person obtaining a
- * copy of this software and associated documentation files (the "Software"),
- * to deal in the Software without restriction, including without limitation
- * the rights to use, copy, modify, merge, publish, distribute, sublicense,
- * and/or sell copies of the Software, and to permit persons to whom the
- * Software is furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice (including the next
- * paragraph) shall be included in all copies or substantial portions of the
- * Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
- * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
- * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
- * DEALINGS
- * IN THE SOFTWARE.
- *
  */
 
 #define pr_fmt(fmt) "vgaarb: " fmt
-- 
2.27.0

[PATCH V4 03/10] PCI/VGA: Use unsigned format string to print lock counts

[Huacai Chen]

From: Bjorn Helgaas <bhelgaas@google.com>

In struct vga_device, io_lock_cnt and mem_lock_cnt are unsigned, but we
previously printed them with "%d", the signed decimal format.  Print them
with the unsigned format "%u" instead.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index 61b57abcb014..e4153ab70481 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -1022,7 +1022,7 @@ static ssize_t vga_arb_read(struct file *file, char __user *buf,
 
 	/* Fill the buffer with infos */
 	len = snprintf(lbuf, 1024,
-		       "count:%d,PCI:%s,decodes=%s,owns=%s,locks=%s(%d:%d)\n",
+		       "count:%d,PCI:%s,decodes=%s,owns=%s,locks=%s(%u:%u)\n",
 		       vga_decode_count, pci_name(pdev),
 		       vga_iostate_to_str(vgadev->decodes),
 		       vga_iostate_to_str(vgadev->owns),
-- 
2.27.0

[PATCH V4 04/10] PCI/VGA: Remove empty vga_arb_device_card_gone()

[Huacai Chen]

From: Bjorn Helgaas <bhelgaas@google.com>

vga_arb_device_card_gone() has always been empty.  Remove it.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index e4153ab70481..c984c76b3fd7 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -104,8 +104,6 @@ static int vga_str_to_iostate(char *buf, int str_size, int *io_state)
 /* this is only used a cookie - it should not be dereferenced */
 static struct pci_dev *vga_default;
 
-static void vga_arb_device_card_gone(struct pci_dev *pdev);
-
 /* Find somebody in our list */
 static struct vga_device *vgadev_find(struct pci_dev *pdev)
 {
@@ -741,10 +739,6 @@ static bool vga_arbiter_del_pci_device(struct pci_dev *pdev)
 	/* Remove entry from list */
 	list_del(&vgadev->list);
 	vga_count--;
-	/* Notify userland driver that the device is gone so it discards
-	 * it's copies of the pci_dev pointer
-	 */
-	vga_arb_device_card_gone(pdev);
 
 	/* Wake up all possible waiters */
 	wake_up_all(&vga_wait_queue);
@@ -994,9 +988,7 @@ static ssize_t vga_arb_read(struct file *file, char __user *buf,
 	if (lbuf == NULL)
 		return -ENOMEM;
 
-	/* Shields against vga_arb_device_card_gone (pci_dev going
-	 * away), and allows access to vga list
-	 */
+	/* Protects vga_list */
 	spin_lock_irqsave(&vga_lock, flags);
 
 	/* If we are targeting the default, use it */
@@ -1013,8 +1005,6 @@ static ssize_t vga_arb_read(struct file *file, char __user *buf,
 		/* Wow, it's not in the list, that shouldn't happen,
 		 * let's fix us up and return invalid card
 		 */
-		if (pdev == priv->target)
-			vga_arb_device_card_gone(pdev);
 		spin_unlock_irqrestore(&vga_lock, flags);
 		len = sprintf(lbuf, "invalid");
 		goto done;
@@ -1358,10 +1348,6 @@ static int vga_arb_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
-static void vga_arb_device_card_gone(struct pci_dev *pdev)
-{
-}
-
 /*
  * callback any registered clients to let them know we have a
  * change in VGA cards
-- 
2.27.0

[PATCH V4 05/10] PCI/VGA: Move vga_arb_integrated_gpu() earlier in file

[Huacai Chen]

Move vga_arb_integrated_gpu() earlier in file to prepare for future patch.
No functional change intended.

[bhelgaas: split to separate patch]
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index c984c76b3fd7..1f8fb37be5fa 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -563,6 +563,20 @@ void vga_put(struct pci_dev *pdev, unsigned int rsrc)
 }
 EXPORT_SYMBOL(vga_put);
 
+#if defined(CONFIG_ACPI)
+static bool vga_arb_integrated_gpu(struct device *dev)
+{
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+
+	return adev && !strcmp(acpi_device_hid(adev), ACPI_VIDEO_HID);
+}
+#else
+static bool vga_arb_integrated_gpu(struct device *dev)
+{
+	return false;
+}
+#endif
+
 /*
  * Rules for using a bridge to control a VGA descendant decoding: if a bridge
  * has only one VGA descendant then it can be used to control the VGA routing
@@ -1416,20 +1430,6 @@ static struct miscdevice vga_arb_device = {
 	MISC_DYNAMIC_MINOR, "vga_arbiter", &vga_arb_device_fops
 };
 
-#if defined(CONFIG_ACPI)
-static bool vga_arb_integrated_gpu(struct device *dev)
-{
-	struct acpi_device *adev = ACPI_COMPANION(dev);
-
-	return adev && !strcmp(acpi_device_hid(adev), ACPI_VIDEO_HID);
-}
-#else
-static bool vga_arb_integrated_gpu(struct device *dev)
-{
-	return false;
-}
-#endif
-
 static void __init vga_arb_select_default_device(void)
 {
 	struct pci_dev *pdev, *found = NULL;
-- 
2.27.0

[PATCH V4 06/10] PCI/VGA: Prefer vga_default_device()

[Huacai Chen]

Use the vga_default_device() interface consistently instead of directly
testing vga_default.  No functional change intended.

[bhelgaas: split to separate patch and extended]
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index 1f8fb37be5fa..a6a5864ff538 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -173,7 +173,7 @@ int vga_remove_vgacon(struct pci_dev *pdev)
 {
 	int ret = 0;
 
-	if (pdev != vga_default)
+	if (pdev != vga_default_device())
 		return 0;
 	vgaarb_info(&pdev->dev, "deactivate vga console\n");
 
@@ -707,7 +707,7 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
 	/* Deal with VGA default device. Use first enabled one
 	 * by default if arch doesn't have it's own hook
 	 */
-	if (vga_default == NULL &&
+	if (!vga_default_device() &&
 	    ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
 		vgaarb_info(&pdev->dev, "setting as boot VGA device\n");
 		vga_set_default_device(pdev);
@@ -744,7 +744,7 @@ static bool vga_arbiter_del_pci_device(struct pci_dev *pdev)
 		goto bail;
 	}
 
-	if (vga_default == pdev)
+	if (vga_default_device() == pdev)
 		vga_set_default_device(NULL);
 
 	if (vgadev->decodes & (VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM))
-- 
2.27.0

[PATCH V4 07/10] PCI/VGA: Split out vga_arb_update_default_device()

[Huacai Chen]

If there's no default VGA device, and we find a VGA device that owns the
legacy VGA resources, we make that device the default.  Split this logic
out from vga_arbiter_add_pci_device() into a new function,
vga_arb_update_default_device().

[bhelgaas: split another piece to separate patch]
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index a6a5864ff538..4cecb599f5ed 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -577,6 +577,21 @@ static bool vga_arb_integrated_gpu(struct device *dev)
 }
 #endif
 
+static void vga_arb_update_default_device(struct vga_device *vgadev)
+{
+	struct pci_dev *pdev = vgadev->pdev;
+
+	/*
+	 * If we don't have a default VGA device yet, and this device owns
+	 * the legacy VGA resources, make it the default.
+	 */
+	if (!vga_default_device() &&
+	    ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
+		vgaarb_info(&pdev->dev, "setting as boot VGA device\n");
+		vga_set_default_device(pdev);
+	}
+}
+
 /*
  * Rules for using a bridge to control a VGA descendant decoding: if a bridge
  * has only one VGA descendant then it can be used to control the VGA routing
@@ -704,15 +719,7 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
 		bus = bus->parent;
 	}
 
-	/* Deal with VGA default device. Use first enabled one
-	 * by default if arch doesn't have it's own hook
-	 */
-	if (!vga_default_device() &&
-	    ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
-		vgaarb_info(&pdev->dev, "setting as boot VGA device\n");
-		vga_set_default_device(pdev);
-	}
-
+	vga_arb_update_default_device(vgadev);
 	vga_arbiter_check_bridge_sharing(vgadev);
 
 	/* Add to the list */
-- 
2.27.0

[PATCH V4 08/10] PCI/VGA: Log bridge control messages when adding devices

[Huacai Chen]

Previously vga_arb_device_init() iterated through all VGA devices and
indicated whether legacy VGA routing to each could be controlled by an
upstream bridge.

But we determine that information in vga_arbiter_add_pci_device(), which we
call for every device, so we can log it there without iterating through the
VGA devices again.

Note that we call vga_arbiter_check_bridge_sharing() before adding the
device to vga_list, so we have to handle the very first device separately.

[bhelgaas: commit log, split another piece to separate patch, fix
list_empty() issue]
Link: https://lore.kernel.org/r/20210705100503.1120643-1-chenhuacai@loongson.cn
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index 4cecb599f5ed..dd07b1c3205f 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -609,8 +609,10 @@ static void vga_arbiter_check_bridge_sharing(struct vga_device *vgadev)
 
 	vgadev->bridge_has_one_vga = true;
 
-	if (list_empty(&vga_list))
+	if (list_empty(&vga_list)) {
+		vgaarb_info(&vgadev->pdev->dev, "bridge control possible\n");
 		return;
+	}
 
 	/* okay iterate the new devices bridge hierarachy */
 	new_bus = vgadev->pdev->bus;
@@ -649,6 +651,11 @@ static void vga_arbiter_check_bridge_sharing(struct vga_device *vgadev)
 		}
 		new_bus = new_bus->parent;
 	}
+
+	if (vgadev->bridge_has_one_vga)
+		vgaarb_info(&vgadev->pdev->dev, "bridge control possible\n");
+	else
+		vgaarb_info(&vgadev->pdev->dev, "no bridge control possible\n");
 }
 
 /*
@@ -1527,7 +1534,6 @@ static int __init vga_arb_device_init(void)
 {
 	int rc;
 	struct pci_dev *pdev;
-	struct vga_device *vgadev;
 
 	rc = misc_register(&vga_arb_device);
 	if (rc < 0)
@@ -1543,15 +1549,6 @@ static int __init vga_arb_device_init(void)
 			       PCI_ANY_ID, pdev)) != NULL)
 		vga_arbiter_add_pci_device(pdev);
 
-	list_for_each_entry(vgadev, &vga_list, list) {
-		struct device *dev = &vgadev->pdev->dev;
-
-		if (vgadev->bridge_has_one_vga)
-			vgaarb_info(dev, "bridge control possible\n");
-		else
-			vgaarb_info(dev, "no bridge control possible\n");
-	}
-
 	vga_arb_select_default_device();
 
 	pr_info("loaded\n");
-- 
2.27.0

[PATCH V4 09/10] PCI/VGA: Rework default VGA device selection (Step 1)

[Huacai Chen]

Current default VGA device selection fails in some cases:

  - On BMC system, the AST2500 bridge [1a03:1150] does not implement
    PCI_BRIDGE_CTL_VGA [1].  This is perfectly legal but means the
    legacy VGA resources won't reach downstream devices unless they're
    included in the usual bridge windows.

  - vga_arb_select_default_device() will set a device below such a
    bridge as the default VGA device as long as it has PCI_COMMAND_IO
    and PCI_COMMAND_MEMORY enabled.

  - vga_arbiter_add_pci_device() is called for every VGA device,
    either at boot-time or at hot-add time, and it will also set the
    device as the default VGA device, but ONLY if all bridges leading
    to it implement PCI_BRIDGE_CTL_VGA.

  - This difference between vga_arb_select_default_device() and
    vga_arbiter_add_pci_device() means that a device below an AST2500
    or similar bridge can only be set as the default if it is
    enumerated before vga_arb_device_init().

  - On ACPI-based systems, PCI devices are enumerated by acpi_init(),
    which runs before vga_arb_device_init().

  - On non-ACPI systems, like on MIPS system, they are enumerated by
    pcibios_init(), which typically runs *after*
    vga_arb_device_init().

So I made vga_arb_update_default_device() to replace the current vga_
arb_select_default_device(), which will be call from vga_arbiter_add_
pci_device(), set the default device even if it does not own the VGA
resources because an upstream bridge doesn't implement PCI_BRIDGE_CTL_
VGA. And the default VGA device is updated if a better one is found
(device with legacy resources enabled is better, device owns the
firmware framebuffer is even better).

This patch is the first step: complete vga_arb_update_default_device().
The logic of selecting the best device is the same as vga_arb_select_
default_device().

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 69 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 66 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index dd07b1c3205f..ee7caee08b1b 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -580,16 +580,79 @@ static bool vga_arb_integrated_gpu(struct device *dev)
 static void vga_arb_update_default_device(struct vga_device *vgadev)
 {
 	struct pci_dev *pdev = vgadev->pdev;
+	struct device *dev = &pdev->dev;
+	struct vga_device *vgadev_default;
+#if defined(CONFIG_X86) || defined(CONFIG_IA64)
+	int i;
+	unsigned long flags;
+	u64 base = screen_info.lfb_base;
+	u64 size = screen_info.lfb_size;
+	u64 limit;
+	resource_size_t start, end;
+#endif
 
 	/*
 	 * If we don't have a default VGA device yet, and this device owns
 	 * the legacy VGA resources, make it the default.
 	 */
-	if (!vga_default_device() &&
-	    ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
-		vgaarb_info(&pdev->dev, "setting as boot VGA device\n");
+	if (!vga_default_device()) {
+		if ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)
+			vgaarb_info(dev, "setting as boot VGA device\n");
+		else
+			vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
+		vga_set_default_device(pdev);
+	}
+
+	vgadev_default = vgadev_find(vga_default);
+
+	/* Overridden by a better device */
+	if (vgadev_default && ((vgadev_default->owns & VGA_RSRC_LEGACY_MASK) == 0)
+		&& ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
+		vgaarb_info(dev, "overriding boot VGA device\n");
 		vga_set_default_device(pdev);
 	}
+
+	if (vga_arb_integrated_gpu(dev)) {
+		vgaarb_info(dev, "overriding boot VGA device\n");
+		vga_set_default_device(pdev);
+	}
+
+#if defined(CONFIG_X86) || defined(CONFIG_IA64)
+	if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
+		base |= (u64)screen_info.ext_lfb_base << 32;
+
+	limit = base + size;
+
+	/*
+	 * Override vga_arbiter_add_pci_device()'s I/O based detection
+	 * as it may take the wrong device (e.g. on Apple system under
+	 * EFI).
+	 *
+	 * Select the device owning the boot framebuffer if there is
+	 * one.
+	 */
+
+	/* Does firmware framebuffer belong to us? */
+	for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
+		flags = pci_resource_flags(vgadev->pdev, i);
+
+		if ((flags & IORESOURCE_MEM) == 0)
+			continue;
+
+		start = pci_resource_start(vgadev->pdev, i);
+		end  = pci_resource_end(vgadev->pdev, i);
+
+		if (!start || !end)
+			continue;
+
+		if (base < start || limit >= end)
+			continue;
+
+		if (vgadev->pdev != vga_default_device())
+			vgaarb_info(dev, "overriding boot device\n");
+		vga_set_default_device(vgadev->pdev);
+	}
+#endif
 }
 
 /*
-- 
2.27.0

[PATCH V4 10/10] PCI/VGA: Rework default VGA device selection (Step 2)

[Huacai Chen]

Current default VGA device selection fails in some cases:

  - On BMC system, the AST2500 bridge [1a03:1150] does not implement
    PCI_BRIDGE_CTL_VGA [1].  This is perfectly legal but means the
    legacy VGA resources won't reach downstream devices unless they're
    included in the usual bridge windows.

  - vga_arb_select_default_device() will set a device below such a
    bridge as the default VGA device as long as it has PCI_COMMAND_IO
    and PCI_COMMAND_MEMORY enabled.

  - vga_arbiter_add_pci_device() is called for every VGA device,
    either at boot-time or at hot-add time, and it will also set the
    device as the default VGA device, but ONLY if all bridges leading
    to it implement PCI_BRIDGE_CTL_VGA.

  - This difference between vga_arb_select_default_device() and
    vga_arbiter_add_pci_device() means that a device below an AST2500
    or similar bridge can only be set as the default if it is
    enumerated before vga_arb_device_init().

  - On ACPI-based systems, PCI devices are enumerated by acpi_init(),
    which runs before vga_arb_device_init().

  - On non-ACPI systems, like on MIPS system, they are enumerated by
    pcibios_init(), which typically runs *after*
    vga_arb_device_init().

So I made vga_arb_update_default_device() to replace the current vga_
arb_select_default_device(), which will be call from vga_arbiter_add_
pci_device(), set the default device even if it does not own the VGA
resources because an upstream bridge doesn't implement PCI_BRIDGE_CTL_
VGA. And the default VGA device is updated if a better one is found
(device with legacy resources enabled is better, device owns the
firmware framebuffer is even better).

This patch is the second step: remove vga_arb_select_default_device()
and its call-site.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/vgaarb.c | 89 --------------------------------------------
 1 file changed, 89 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index ee7caee08b1b..0b059a2fc749 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -1507,92 +1507,6 @@ static struct miscdevice vga_arb_device = {
 	MISC_DYNAMIC_MINOR, "vga_arbiter", &vga_arb_device_fops
 };
 
-static void __init vga_arb_select_default_device(void)
-{
-	struct pci_dev *pdev, *found = NULL;
-	struct vga_device *vgadev;
-
-#if defined(CONFIG_X86) || defined(CONFIG_IA64)
-	u64 base = screen_info.lfb_base;
-	u64 size = screen_info.lfb_size;
-	u64 limit;
-	resource_size_t start, end;
-	unsigned long flags;
-	int i;
-
-	if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
-		base |= (u64)screen_info.ext_lfb_base << 32;
-
-	limit = base + size;
-
-	list_for_each_entry(vgadev, &vga_list, list) {
-		struct device *dev = &vgadev->pdev->dev;
-		/*
-		 * Override vga_arbiter_add_pci_device()'s I/O based detection
-		 * as it may take the wrong device (e.g. on Apple system under
-		 * EFI).
-		 *
-		 * Select the device owning the boot framebuffer if there is
-		 * one.
-		 */
-
-		/* Does firmware framebuffer belong to us? */
-		for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
-			flags = pci_resource_flags(vgadev->pdev, i);
-
-			if ((flags & IORESOURCE_MEM) == 0)
-				continue;
-
-			start = pci_resource_start(vgadev->pdev, i);
-			end  = pci_resource_end(vgadev->pdev, i);
-
-			if (!start || !end)
-				continue;
-
-			if (base < start || limit >= end)
-				continue;
-
-			if (!vga_default_device())
-				vgaarb_info(dev, "setting as boot device\n");
-			else if (vgadev->pdev != vga_default_device())
-				vgaarb_info(dev, "overriding boot device\n");
-			vga_set_default_device(vgadev->pdev);
-		}
-	}
-#endif
-
-	if (!vga_default_device()) {
-		list_for_each_entry_reverse(vgadev, &vga_list, list) {
-			struct device *dev = &vgadev->pdev->dev;
-			u16 cmd;
-
-			pdev = vgadev->pdev;
-			pci_read_config_word(pdev, PCI_COMMAND, &cmd);
-			if (cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) {
-				found = pdev;
-				if (vga_arb_integrated_gpu(dev))
-					break;
-			}
-		}
-	}
-
-	if (found) {
-		vgaarb_info(&found->dev, "setting as boot device (VGA legacy resources not available)\n");
-		vga_set_default_device(found);
-		return;
-	}
-
-	if (!vga_default_device()) {
-		vgadev = list_first_entry_or_null(&vga_list,
-						  struct vga_device, list);
-		if (vgadev) {
-			struct device *dev = &vgadev->pdev->dev;
-			vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
-			vga_set_default_device(vgadev->pdev);
-		}
-	}
-}
-
 static int __init vga_arb_device_init(void)
 {
 	int rc;
@@ -1612,9 +1526,6 @@ static int __init vga_arb_device_init(void)
 			       PCI_ANY_ID, pdev)) != NULL)
 		vga_arbiter_add_pci_device(pdev);
 
-	vga_arb_select_default_device();
-
-	pr_info("loaded\n");
 	return rc;
 }
 subsys_initcall(vga_arb_device_init);
-- 
2.27.0

Re: [PATCH V4 00/10] PCI/VGA: Rework default VGA device selection

[Bjorn Helgaas]

On Fri, Aug 27, 2021 at 04:31:19PM +0800, Huacai Chen wrote:
> My original work is at [1].
> 
> Bjorn do some rework and extension in V2. It moves the VGA arbiter to
> the PCI subsystem, fixes a few nits, and breaks a few pieces to make
> the main patch a little smaller.
> 
> V3 rewrite the commit log of the last patch (which is also summarized
> by Bjorn).
> 
> V4 split the last patch to two steps.
> 
> All comments welcome!

I'm hoping to apply something like this for v5.16.

BUT as I mentioned in [2], I want the very first patch to be the very
simple 2-line change to vga_arb_update_default_device() that actually
fixes your problem.

It makes no sense for that change to be at the very end, hidden in the
middle of a bigger restructuring patch.

[2] https://lore.kernel.org/r/20210825201704.GA3600046@bjorn-Precision-5520

> [1] https://lore.kernel.org/dri-devel/20210705100503.1120643-1-chenhuacai@loongson.cn/
> 
> Bjorn Helgaas (4):
>   PCI/VGA: Move vgaarb to drivers/pci
>   PCI/VGA: Replace full MIT license text with SPDX identifier
>   PCI/VGA: Use unsigned format string to print lock counts
>   PCI/VGA: Remove empty vga_arb_device_card_gone()
> 
> Huacai Chen (6):
>   PCI/VGA: Move vga_arb_integrated_gpu() earlier in file
>   PCI/VGA: Prefer vga_default_device()
>   PCI/VGA: Split out vga_arb_update_default_device()
>   PCI/VGA: Log bridge control messages when adding devices
>   PCI/VGA: Rework default VGA device selection (Step 1)
>   PCI/VGA: Rework default VGA device selection (Step 2)
> 
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> 
> ---
>  drivers/gpu/vga/Kconfig           |  19 ---
>  drivers/gpu/vga/Makefile          |   1 -
>  drivers/pci/Kconfig               |  19 +++
>  drivers/pci/Makefile              |   1 +
>  drivers/{gpu/vga => pci}/vgaarb.c | 269 ++++++++++++------------------
>  5 files changed, 126 insertions(+), 183 deletions(-)
>  rename drivers/{gpu/vga => pci}/vgaarb.c (90%)
> --
> 2.27.0
> 

Re: [PATCH V4 00/10] PCI/VGA: Rework default VGA device selection

[Huacai Chen]

Hi, Bjorn,

On Fri, Sep 10, 2021 at 1:59 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Fri, Aug 27, 2021 at 04:31:19PM +0800, Huacai Chen wrote:
> > My original work is at [1].
> >
> > Bjorn do some rework and extension in V2. It moves the VGA arbiter to
> > the PCI subsystem, fixes a few nits, and breaks a few pieces to make
> > the main patch a little smaller.
> >
> > V3 rewrite the commit log of the last patch (which is also summarized
> > by Bjorn).
> >
> > V4 split the last patch to two steps.
> >
> > All comments welcome!
>
> I'm hoping to apply something like this for v5.16.
>
> BUT as I mentioned in [2], I want the very first patch to be the very
> simple 2-line change to vga_arb_update_default_device() that actually
> fixes your problem.
>
> It makes no sense for that change to be at the very end, hidden in the
> middle of a bigger restructuring patch.
I think I should split the restructuring patch again, and sort the
series to move important things to earlier patches. Let me try...

Huacai
>
> [2] https://lore.kernel.org/r/20210825201704.GA3600046@bjorn-Precision-5520
>
> > [1] https://lore.kernel.org/dri-devel/20210705100503.1120643-1-chenhuacai@loongson.cn/
> >
> > Bjorn Helgaas (4):
> >   PCI/VGA: Move vgaarb to drivers/pci
> >   PCI/VGA: Replace full MIT license text with SPDX identifier
> >   PCI/VGA: Use unsigned format string to print lock counts
> >   PCI/VGA: Remove empty vga_arb_device_card_gone()
> >
> > Huacai Chen (6):
> >   PCI/VGA: Move vga_arb_integrated_gpu() earlier in file
> >   PCI/VGA: Prefer vga_default_device()
> >   PCI/VGA: Split out vga_arb_update_default_device()
> >   PCI/VGA: Log bridge control messages when adding devices
> >   PCI/VGA: Rework default VGA device selection (Step 1)
> >   PCI/VGA: Rework default VGA device selection (Step 2)
> >
> > Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > ---
> >  drivers/gpu/vga/Kconfig           |  19 ---
> >  drivers/gpu/vga/Makefile          |   1 -
> >  drivers/pci/Kconfig               |  19 +++
> >  drivers/pci/Makefile              |   1 +
> >  drivers/{gpu/vga => pci}/vgaarb.c | 269 ++++++++++++------------------
> >  5 files changed, 126 insertions(+), 183 deletions(-)
> >  rename drivers/{gpu/vga => pci}/vgaarb.c (90%)
> > --
> > 2.27.0
> >