[PATCH v4] PCI: Support hibmc VGA cards behind a misbehaving HiSilicon bridge

[Daniel Axtens <dja@axtens.net>]

The HiSilicon D05 board has some PCI bridges (PCI ID 19e5:1610) that
are not spec-compliant: the VGA Enable bit is hardwired to 0 and
writes do not change it.

The HiSilicon engineers report that the bridge does not forward the
0xa0000-0xbffff mem range and the 0x3b0-0x3bb and 0x3c0-0x3df I/O
ranges.

Because the VGA Enable bit is hardwired to 0, the VGA arbiter refuses
to mark any card behind it as the boot device. This breaks Xorg
auto-detection.

However, the hibmc VGA card (PCI ID 19e5:1711) has been tested and is
known to work when behind these bridges. (It does not require the
legacy resources to operate.)

Provide a quirk so that this combination of bridge and card is eligible
to be the default VGA card. This fixes Xorg auto-detection on the D05.

Cc: Xinliang Liu <z.liuxinliang@hisilicon.com>
Cc: Rongrong Zou <zourongrong@gmail.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---

v3: fix commit message
v4: fix comment (forgot to git add/git commit, sorry for the noise)

---
 drivers/pci/quirks.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 16e6cd86ad71..b42324cba29e 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -25,6 +25,7 @@
 #include <linux/sched.h>
 #include <linux/ktime.h>
 #include <linux/mm.h>
+#include <linux/vgaarb.h>
 #include <asm/dma.h>	/* isa_dma_bridge_buggy */
 #include "pci.h"
 
@@ -4664,3 +4665,52 @@ static void quirk_intel_no_flr(struct pci_dev *dev)
 }
 DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1502, quirk_intel_no_flr);
 DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1503, quirk_intel_no_flr);
+
+/*
+ * The HiSilicon D05 board has some PCI bridges (PCI ID 19e5:1610)
+ * that are not spec-compliant: the VGA Enable bit is hardwired to 0
+ * and writes do not change it. The bridge does not forward legacy
+ * memory or I/O resources.
+ *
+ * Because the VGA Enable bit is hardwired to 0, the VGA arbiter
+ * refuses to mark any card behind it as the boot device. However, the
+ * hibmc VGA card (PCI ID 19e5:1711) has been tested and is known to
+ * work when behind these bridges.
+ *
+ * If we have this bridge, this card, and no default card already,
+ * mark the card as default.
+ */
+static void hibmc_fixup_vgaarb(struct pci_dev *pdev)
+{
+	struct pci_dev *bridge;
+	struct pci_bus *bus;
+	u16 config;
+
+	bus = pdev->bus;
+	bridge = bus->self;
+	if (!bridge)
+		return;
+
+	if (!pci_is_bridge(bridge))
+		return;
+
+	if (bridge->vendor != PCI_VENDOR_ID_HUAWEI ||
+	    bridge->device != 0x1610)
+		return;
+
+	pci_read_config_word(bridge, PCI_BRIDGE_CONTROL,
+			     &config);
+	if (config & PCI_BRIDGE_CTL_VGA) {
+		/*
+		 * Weirdly, this bridge *is* spec compliant, so bail
+		 * and let vgaarb do its job
+		 */
+		return;
+	}
+
+	if (vga_default_device())
+		return;
+
+	vga_set_default_device(pdev);
+}
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_HUAWEI, 0x1711, hibmc_fixup_vgaarb);
-- 
2.11.0