[PATCH 0/2] vgaarb: Select fallback default VGA device

[PATCH 0/2] vgaarb: Select fallback default VGA device

[Bjorn Helgaas]

These patches are supposed to fix a problem Daniel Axtens found on the
HiSilicon D05 board.  The VGA device there is behind a bridge that doesn't
support PCI_BRIDGE_CTL_VGA, so the arbiter never selects the device as the
default.

The first patch extends the arbiter so that if it can't find an enabled VGA
device with legacy resources, it selects the first enabled device *without*
legacy resources (this is what fixes the D05).  If that fails, it selects
the first device that isn't enabled.  The combination of both changes
should make the current powerpc fixup_vga() quirk unnecessary.

N.B. It changes the powerpc behavior: if there are several enabled VGA
devices, the current quirk selects the last one, while this patch selects
the first one.  If this is a problem, I can drop that part of the patch and
keep the quirk.

The second patch pulls out this fallback device detection (and the EFI
override) from vga_arb_device_init() to make it easier to read.

---

Bjorn Helgaas (2):
      vgaarb: Select a default VGA device even if there's no legacy VGA
      vgaarb: Factor out EFI and fallback default device selection


 arch/powerpc/kernel/pci-common.c |   12 ------
 drivers/gpu/vga/vgaarb.c         |   72 +++++++++++++++++++++++++++++---------
 2 files changed, 55 insertions(+), 29 deletions(-)

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[PATCH 1/2] vgaarb: Select a default VGA device even if there's no legacy VGA

[Bjorn Helgaas]

From: Bjorn Helgaas <bhelgaas@google.com>

Daniel Axtens reported that on the HiSilicon D05 board, the VGA device is
behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so the VGA arbiter
never selects it as the default, which means Xorg auto-detection doesn't
work.

VGA is a legacy PCI feature: a VGA device can respond to addresses, e.g.,
[mem 0xa0000-0xbffff], [io 0x3b0-0x3bb], [io 0x3c0-0x3df], etc., that are
not configurable by BARs.  Consequently, multiple VGA devices can conflict
with each other.  The VGA arbiter avoids conflicts by ensuring that those
legacy resources are only routed to one VGA device at a time.

The arbiter identifies the "default VGA" device, i.e., a legacy VGA device
that was used by boot firmware.  It selects the first device that:

  - is of PCI_CLASS_DISPLAY_VGA,
  - has both PCI_COMMAND_IO and PCI_COMMAND_MEMORY enabled, and
  - has PCI_BRIDGE_CTL_VGA set in all upstream bridges.

Some systems don't have such a device.  For example, if a host bridge
doesn't support I/O space, PCI_COMMAND_IO probably won't be enabled for any
devices below it.  Or, as on the HiSilicon D05, the VGA device may be
behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so accesses to the
legacy VGA resources will never reach the device.

This patch extends the arbiter so that if it doesn't find a device that
meets all the above criteria, it selects the first device that:

  - is of PCI_CLASS_DISPLAY_VGA and
  - has PCI_COMMAND_IO or PCI_COMMAND_MEMORY enabled

If it doesn't find even that, it selects the first device that:

  - is of class PCI_CLASS_DISPLAY_VGA.

Such a device may not be able to use the legacy VGA resources, but most
drivers can operate the device without those.  Setting it as the default
device means its "boot_vga" sysfs file will contain "1", which Xorg (via
libpciaccess) uses to help select its default output device.

This fixes Xorg auto-detection on some arm64 systems (HiSilicon D05 in
particular; see the link below).

It also replaces the powerpc fixup_vga() quirk, albeit with slightly
different semantics: the quirk selected the first VGA device we found, and
overrode that selection with any enabled VGA device we found.  If there
were several enabled VGA devices, the *last* one we found would become the
default.

The code here instead selects the *first* enabled VGA device we find, and
if none are enabled, the first VGA device we find.

Link: http://lkml.kernel.org/r/20170901072744.2409-1-dja@axtens.net
Tested-by: Daniel Axtens <dja@axtens.net>    # arm64, ppc64-qemu-tcg
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 arch/powerpc/kernel/pci-common.c |   12 ------------
 drivers/gpu/vga/vgaarb.c         |   25 +++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index 02831a396419..0ac7aa346c69 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -1740,15 +1740,3 @@ static void fixup_hide_host_resource_fsl(struct pci_dev *dev)
 }
 DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MOTOROLA, PCI_ANY_ID, fixup_hide_host_resource_fsl);
 DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_FREESCALE, PCI_ANY_ID, fixup_hide_host_resource_fsl);
-
-static void fixup_vga(struct pci_dev *pdev)
-{
-	u16 cmd;
-
-	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
-	if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device())
-		vga_set_default_device(pdev);
-
-}
-DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_ANY_ID, PCI_ANY_ID,
-			      PCI_CLASS_DISPLAY_VGA, 8, fixup_vga);
diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
index 76875f6299b8..aeb41f793ed4 100644
--- a/drivers/gpu/vga/vgaarb.c
+++ b/drivers/gpu/vga/vgaarb.c
@@ -1468,6 +1468,31 @@ static int __init vga_arb_device_init(void)
 			vgaarb_info(dev, "no bridge control possible\n");
 	}
 
+	if (!vga_default_device()) {
+		list_for_each_entry(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)) {
+				vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
+				vga_set_default_device(pdev);
+				break;
+			}
+		}
+	}
+
+	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(pdev);
+		}
+	}
+
 	pr_info("loaded\n");
 	return rc;
 }

[PATCH 2/2] vgaarb: Factor out EFI and fallback default device selection

[Bjorn Helgaas]

From: Bjorn Helgaas <bhelgaas@google.com>

The default VGA device is normally set in vga_arbiter_add_pci_device() when
we call it for the first enabled device that can be accessed with the
legacy VGA resources ([mem 0xa0000-0xbffff], etc.)

That default device can be overridden by an EFI device that owns the boot
framebuffer.  As a fallback, we can also select a VGA device that can't be
accessed via legacy VGA resources, or a VGA device that isn't even enabled.

Factor out this EFI and fallback selection from vga_arb_device_init() into
a separate vga_arb_select_default_device() function.  This doesn't change
any behavior, but it untangles the "bridge control possible" checking and
messages from the default device selection.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/gpu/vga/vgaarb.c |   57 ++++++++++++++++++++++++++++------------------
 1 file changed, 35 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
index aeb41f793ed4..7803e35a3702 100644
--- a/drivers/gpu/vga/vgaarb.c
+++ b/drivers/gpu/vga/vgaarb.c
@@ -1402,29 +1402,14 @@ static struct miscdevice vga_arb_device = {
 	MISC_DYNAMIC_MINOR, "vga_arbiter", &vga_arb_device_fops
 };
 
-static int __init vga_arb_device_init(void)
+static void __init vga_arb_select_default_device(void)
 {
-	int rc;
 	struct pci_dev *pdev;
 	struct vga_device *vgadev;
 
-	rc = misc_register(&vga_arb_device);
-	if (rc < 0)
-		pr_err("error %d registering device\n", rc);
-
-	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);
-
+#if defined(CONFIG_X86) || defined(CONFIG_IA64)
 	list_for_each_entry(vgadev, &vga_list, list) {
 		struct device *dev = &vgadev->pdev->dev;
-#if defined(CONFIG_X86) || defined(CONFIG_IA64)
 		/*
 		 * Override vga_arbiter_add_pci_device()'s I/O based detection
 		 * as it may take the wrong device (e.g. on Apple system under
@@ -1461,12 +1446,8 @@ static int __init vga_arb_device_init(void)
 				vgaarb_info(dev, "overriding boot device\n");
 			vga_set_default_device(vgadev->pdev);
 		}
-#endif
-		if (vgadev->bridge_has_one_vga)
-			vgaarb_info(dev, "bridge control possible\n");
-		else
-			vgaarb_info(dev, "no bridge control possible\n");
 	}
+#endif
 
 	if (!vga_default_device()) {
 		list_for_each_entry(vgadev, &vga_list, list) {
@@ -1492,6 +1473,38 @@ static int __init vga_arb_device_init(void)
 			vga_set_default_device(pdev);
 		}
 	}
+}
+
+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)
+		pr_err("error %d registering device\n", rc);
+
+	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);
+
+	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");
 	return rc;

Re: [PATCH 0/2] vgaarb: Select fallback default VGA device

[Sherlock Wang]

On Fri, Oct 06, 2017 at 05:24:20PM -0500, Bjorn Helgaas wrote:
> These patches are supposed to fix a problem Daniel Axtens found on the
> HiSilicon D05 board.  The VGA device there is behind a bridge that doesn't
> support PCI_BRIDGE_CTL_VGA, so the arbiter never selects the device as the
> default.
> 
> The first patch extends the arbiter so that if it can't find an enabled VGA
> device with legacy resources, it selects the first enabled device *without*
> legacy resources (this is what fixes the D05).  If that fails, it selects
> the first device that isn't enabled.  The combination of both changes
> should make the current powerpc fixup_vga() quirk unnecessary.
> 
> N.B. It changes the powerpc behavior: if there are several enabled VGA
> devices, the current quirk selects the last one, while this patch selects
> the first one.  If this is a problem, I can drop that part of the patch and
> keep the quirk.
> 
> The second patch pulls out this fallback device detection (and the EFI
> override) from vga_arb_device_init() to make it easier to read.

Hi Bjorn,

I tested this series in:

        D05 board based on HiSilicon SoC Hip07.
        And HiSilicon SoC Hip08 based board.

Both of these two SoCs' PCIe host bridge don't support PCI_BRIDGE_CTL_VGA. One
VGA device which does not support legacy resources has been connected to these
two PCIe host bridges to test. Default VGA device can be selected in above two
systems.

Tested-by: Zhou Wang <wangzhou1@hisilicon.com>
(sorry for my HiSilicon E-mail box miss this serias, so here I have to use my
gmail box)

Thanks,
Zhou

> 
> ---
> 
> Bjorn Helgaas (2):
>       vgaarb: Select a default VGA device even if there's no legacy VGA
>       vgaarb: Factor out EFI and fallback default device selection
> 
> 
>  arch/powerpc/kernel/pci-common.c |   12 ------
>  drivers/gpu/vga/vgaarb.c         |   72 +++++++++++++++++++++++++++++---------
>  2 files changed, 55 insertions(+), 29 deletions(-)

Re: [PATCH 1/2] vgaarb: Select a default VGA device even if there's no legacy VGA

[Julien Thierry]

Hi Bjorn,

On 06/10/17 23:24, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> Daniel Axtens reported that on the HiSilicon D05 board, the VGA device is
> behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so the VGA arbiter
> never selects it as the default, which means Xorg auto-detection doesn't
> work.
> 
> VGA is a legacy PCI feature: a VGA device can respond to addresses, e.g.,
> [mem 0xa0000-0xbffff], [io 0x3b0-0x3bb], [io 0x3c0-0x3df], etc., that are
> not configurable by BARs.  Consequently, multiple VGA devices can conflict
> with each other.  The VGA arbiter avoids conflicts by ensuring that those
> legacy resources are only routed to one VGA device at a time.
> 
> The arbiter identifies the "default VGA" device, i.e., a legacy VGA device
> that was used by boot firmware.  It selects the first device that:
> 
>    - is of PCI_CLASS_DISPLAY_VGA,
>    - has both PCI_COMMAND_IO and PCI_COMMAND_MEMORY enabled, and
>    - has PCI_BRIDGE_CTL_VGA set in all upstream bridges.
> 
> Some systems don't have such a device.  For example, if a host bridge
> doesn't support I/O space, PCI_COMMAND_IO probably won't be enabled for any
> devices below it.  Or, as on the HiSilicon D05, the VGA device may be
> behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so accesses to the
> legacy VGA resources will never reach the device.
> 
> This patch extends the arbiter so that if it doesn't find a device that
> meets all the above criteria, it selects the first device that:
> 
>    - is of PCI_CLASS_DISPLAY_VGA and
>    - has PCI_COMMAND_IO or PCI_COMMAND_MEMORY enabled
> 
> If it doesn't find even that, it selects the first device that:
> 
>    - is of class PCI_CLASS_DISPLAY_VGA.
> 
> Such a device may not be able to use the legacy VGA resources, but most
> drivers can operate the device without those.  Setting it as the default
> device means its "boot_vga" sysfs file will contain "1", which Xorg (via
> libpciaccess) uses to help select its default output device.
> 
> This fixes Xorg auto-detection on some arm64 systems (HiSilicon D05 in
> particular; see the link below).
> 
> It also replaces the powerpc fixup_vga() quirk, albeit with slightly
> different semantics: the quirk selected the first VGA device we found, and
> overrode that selection with any enabled VGA device we found.  If there
> were several enabled VGA devices, the *last* one we found would become the
> default.
> 
> The code here instead selects the *first* enabled VGA device we find, and
> if none are enabled, the first VGA device we find.
> 
> Link: http://lkml.kernel.org/r/20170901072744.2409-1-dja@axtens.net
> Tested-by: Daniel Axtens <dja@axtens.net>    # arm64, ppc64-qemu-tcg
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
>   arch/powerpc/kernel/pci-common.c |   12 ------------
>   drivers/gpu/vga/vgaarb.c         |   25 +++++++++++++++++++++++++
>   2 files changed, 25 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 02831a396419..0ac7aa346c69 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -1740,15 +1740,3 @@ static void fixup_hide_host_resource_fsl(struct pci_dev *dev)
>   }
>   DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MOTOROLA, PCI_ANY_ID, fixup_hide_host_resource_fsl);
>   DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_FREESCALE, PCI_ANY_ID, fixup_hide_host_resource_fsl);
> -
> -static void fixup_vga(struct pci_dev *pdev)
> -{
> -	u16 cmd;
> -
> -	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> -	if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device())
> -		vga_set_default_device(pdev);
> -
> -}
> -DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_ANY_ID, PCI_ANY_ID,
> -			      PCI_CLASS_DISPLAY_VGA, 8, fixup_vga);
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index 76875f6299b8..aeb41f793ed4 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -1468,6 +1468,31 @@ static int __init vga_arb_device_init(void)
>   			vgaarb_info(dev, "no bridge control possible\n");
>   	}
>   
> +	if (!vga_default_device()) {
> +		list_for_each_entry(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)) {
> +				vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
> +				vga_set_default_device(pdev);
> +				break;
> +			}
> +		}
> +	}
> +
> +	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(pdev);

Isn't 'pdev' NULL here? shouldn't it be vgadev->pdev instead?

Cheers,

-- 
Julien Thierry

Re: [PATCH 1/2] vgaarb: Select a default VGA device even if there's no legacy VGA

[Lothar Waßmann]

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Re: [PATCH 1/2] vgaarb: Select a default VGA device even if there's no legacy VGA

[Julien Thierry]

On 12/10/17 13:05, Lothar Waßmann wrote:
> Hi,
> 
> On Thu, 12 Oct 2017 12:24:10 +0100 Julien Thierry wrote:
>> Hi Bjorn,
>>
>> On 06/10/17 23:24, Bjorn Helgaas wrote:
>>> From: Bjorn Helgaas <bhelgaas@google.com>
>>>
>>> Daniel Axtens reported that on the HiSilicon D05 board, the VGA device is
>>> behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so the VGA arbiter
>>> never selects it as the default, which means Xorg auto-detection doesn't
>>> work.
>>>
>>> VGA is a legacy PCI feature: a VGA device can respond to addresses, e.g.,
>>> [mem 0xa0000-0xbffff], [io 0x3b0-0x3bb], [io 0x3c0-0x3df], etc., that are
>>> not configurable by BARs.  Consequently, multiple VGA devices can conflict
>>> with each other.  The VGA arbiter avoids conflicts by ensuring that those
>>> legacy resources are only routed to one VGA device at a time.
>>>
>>> The arbiter identifies the "default VGA" device, i.e., a legacy VGA device
>>> that was used by boot firmware.  It selects the first device that:
>>>
>>>     - is of PCI_CLASS_DISPLAY_VGA,
>>>     - has both PCI_COMMAND_IO and PCI_COMMAND_MEMORY enabled, and
>>>     - has PCI_BRIDGE_CTL_VGA set in all upstream bridges.
>>>
>>> Some systems don't have such a device.  For example, if a host bridge
>>> doesn't support I/O space, PCI_COMMAND_IO probably won't be enabled for any
>>> devices below it.  Or, as on the HiSilicon D05, the VGA device may be
>>> behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so accesses to the
>>> legacy VGA resources will never reach the device.
>>>
>>> This patch extends the arbiter so that if it doesn't find a device that
>>> meets all the above criteria, it selects the first device that:
>>>
>>>     - is of PCI_CLASS_DISPLAY_VGA and
>>>     - has PCI_COMMAND_IO or PCI_COMMAND_MEMORY enabled
>>>
>>> If it doesn't find even that, it selects the first device that:
>>>
>>>     - is of class PCI_CLASS_DISPLAY_VGA.
>>>
>>> Such a device may not be able to use the legacy VGA resources, but most
>>> drivers can operate the device without those.  Setting it as the default
>>> device means its "boot_vga" sysfs file will contain "1", which Xorg (via
>>> libpciaccess) uses to help select its default output device.
>>>
>>> This fixes Xorg auto-detection on some arm64 systems (HiSilicon D05 in
>>> particular; see the link below).
>>>
>>> It also replaces the powerpc fixup_vga() quirk, albeit with slightly
>>> different semantics: the quirk selected the first VGA device we found, and
>>> overrode that selection with any enabled VGA device we found.  If there
>>> were several enabled VGA devices, the *last* one we found would become the
>>> default.
>>>
>>> The code here instead selects the *first* enabled VGA device we find, and
>>> if none are enabled, the first VGA device we find.
>>>
>>> Link: http://lkml.kernel.org/r/20170901072744.2409-1-dja@axtens.net
>>> Tested-by: Daniel Axtens <dja@axtens.net>    # arm64, ppc64-qemu-tcg
>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>> ---
>>>    arch/powerpc/kernel/pci-common.c |   12 ------------
>>>    drivers/gpu/vga/vgaarb.c         |   25 +++++++++++++++++++++++++
>>>    2 files changed, 25 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
>>> index 02831a396419..0ac7aa346c69 100644
>>> --- a/arch/powerpc/kernel/pci-common.c
>>> +++ b/arch/powerpc/kernel/pci-common.c
>>> @@ -1740,15 +1740,3 @@ static void fixup_hide_host_resource_fsl(struct pci_dev *dev)
>>>    }
>>>    DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MOTOROLA, PCI_ANY_ID, fixup_hide_host_resource_fsl);
>>>    DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_FREESCALE, PCI_ANY_ID, fixup_hide_host_resource_fsl);
>>> -
>>> -static void fixup_vga(struct pci_dev *pdev)
>>> -{
>>> -	u16 cmd;
>>> -
>>> -	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
>>> -	if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device())
>>> -		vga_set_default_device(pdev);
>>> -
>>> -}
>>> -DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_ANY_ID, PCI_ANY_ID,
>>> -			      PCI_CLASS_DISPLAY_VGA, 8, fixup_vga);
>>> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
>>> index 76875f6299b8..aeb41f793ed4 100644
>>> --- a/drivers/gpu/vga/vgaarb.c
>>> +++ b/drivers/gpu/vga/vgaarb.c
>>> @@ -1468,6 +1468,31 @@ static int __init vga_arb_device_init(void)
>>>    			vgaarb_info(dev, "no bridge control possible\n");
>>>    	}
>>>    
>>> +	if (!vga_default_device()) {
>>> +		list_for_each_entry(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)) {
>>> +				vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
>>> +				vga_set_default_device(pdev);
>>> +				break;
>>> +			}
>>> +		}
>>> +	}
>>> +
>>> +	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(pdev);
>>
>> Isn't 'pdev' NULL here? shouldn't it be vgadev->pdev instead?
>>
> That cannot not happen, though it isn't quite obvious.
> 'vgadev' will only be non-NULL, when the vga_list isn't empty and in
> that case pdev has been set up in the list_for_each_entry() loop above.
> 

Indeed, it can't be NULL. However, in that case we would be using the 
pdev from the last vgadev in the list whereas this last case suggest we 
are picking the first vgadev in the list. So I don't understand why 
'pdev' is being used rather than 'vgadev-pdev'.

Thanks,

-- 
Julien Thierry

Re: [PATCH 1/2] vgaarb: Select a default VGA device even if there's no legacy VGA

[Bjorn Helgaas]

On Thu, Oct 12, 2017 at 12:24:10PM +0100, Julien Thierry wrote:
> Hi Bjorn,
> 
> On 06/10/17 23:24, Bjorn Helgaas wrote:
> >From: Bjorn Helgaas <bhelgaas@google.com>
> >
> >Daniel Axtens reported that on the HiSilicon D05 board, the VGA device is
> >behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so the VGA arbiter
> >never selects it as the default, which means Xorg auto-detection doesn't
> >work.
> >
> >VGA is a legacy PCI feature: a VGA device can respond to addresses, e.g.,
> >[mem 0xa0000-0xbffff], [io 0x3b0-0x3bb], [io 0x3c0-0x3df], etc., that are
> >not configurable by BARs.  Consequently, multiple VGA devices can conflict
> >with each other.  The VGA arbiter avoids conflicts by ensuring that those
> >legacy resources are only routed to one VGA device at a time.
> >
> >The arbiter identifies the "default VGA" device, i.e., a legacy VGA device
> >that was used by boot firmware.  It selects the first device that:
> >
> >   - is of PCI_CLASS_DISPLAY_VGA,
> >   - has both PCI_COMMAND_IO and PCI_COMMAND_MEMORY enabled, and
> >   - has PCI_BRIDGE_CTL_VGA set in all upstream bridges.
> >
> >Some systems don't have such a device.  For example, if a host bridge
> >doesn't support I/O space, PCI_COMMAND_IO probably won't be enabled for any
> >devices below it.  Or, as on the HiSilicon D05, the VGA device may be
> >behind a bridge that doesn't support PCI_BRIDGE_CTL_VGA, so accesses to the
> >legacy VGA resources will never reach the device.
> >
> >This patch extends the arbiter so that if it doesn't find a device that
> >meets all the above criteria, it selects the first device that:
> >
> >   - is of PCI_CLASS_DISPLAY_VGA and
> >   - has PCI_COMMAND_IO or PCI_COMMAND_MEMORY enabled
> >
> >If it doesn't find even that, it selects the first device that:
> >
> >   - is of class PCI_CLASS_DISPLAY_VGA.
> >
> >Such a device may not be able to use the legacy VGA resources, but most
> >drivers can operate the device without those.  Setting it as the default
> >device means its "boot_vga" sysfs file will contain "1", which Xorg (via
> >libpciaccess) uses to help select its default output device.
> >
> >This fixes Xorg auto-detection on some arm64 systems (HiSilicon D05 in
> >particular; see the link below).
> >
> >It also replaces the powerpc fixup_vga() quirk, albeit with slightly
> >different semantics: the quirk selected the first VGA device we found, and
> >overrode that selection with any enabled VGA device we found.  If there
> >were several enabled VGA devices, the *last* one we found would become the
> >default.
> >
> >The code here instead selects the *first* enabled VGA device we find, and
> >if none are enabled, the first VGA device we find.
> >
> >Link: http://lkml.kernel.org/r/20170901072744.2409-1-dja@axtens.net
> >Tested-by: Daniel Axtens <dja@axtens.net>    # arm64, ppc64-qemu-tcg
> >Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> >---
> >  arch/powerpc/kernel/pci-common.c |   12 ------------
> >  drivers/gpu/vga/vgaarb.c         |   25 +++++++++++++++++++++++++
> >  2 files changed, 25 insertions(+), 12 deletions(-)
> >
> >diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> >index 02831a396419..0ac7aa346c69 100644
> >--- a/arch/powerpc/kernel/pci-common.c
> >+++ b/arch/powerpc/kernel/pci-common.c
> >@@ -1740,15 +1740,3 @@ static void fixup_hide_host_resource_fsl(struct pci_dev *dev)
> >  }
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MOTOROLA, PCI_ANY_ID, fixup_hide_host_resource_fsl);
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_FREESCALE, PCI_ANY_ID, fixup_hide_host_resource_fsl);
> >-
> >-static void fixup_vga(struct pci_dev *pdev)
> >-{
> >-	u16 cmd;
> >-
> >-	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> >-	if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device())
> >-		vga_set_default_device(pdev);
> >-
> >-}
> >-DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_ANY_ID, PCI_ANY_ID,
> >-			      PCI_CLASS_DISPLAY_VGA, 8, fixup_vga);
> >diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> >index 76875f6299b8..aeb41f793ed4 100644
> >--- a/drivers/gpu/vga/vgaarb.c
> >+++ b/drivers/gpu/vga/vgaarb.c
> >@@ -1468,6 +1468,31 @@ static int __init vga_arb_device_init(void)
> >  			vgaarb_info(dev, "no bridge control possible\n");
> >  	}
> >+	if (!vga_default_device()) {
> >+		list_for_each_entry(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)) {
> >+				vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
> >+				vga_set_default_device(pdev);
> >+				break;
> >+			}
> >+		}
> >+	}
> >+
> >+	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(pdev);
> 
> Isn't 'pdev' NULL here? shouldn't it be vgadev->pdev instead?

Yes, vgadev->pdev is what I intended, thanks a lot for pointing that out!

Bjorn