[PATCH v2] efifb: avoid reconfiguration of BAR that covers the framebuffer

[Ard Biesheuvel]

On UEFI systems, the PCI subsystem is enumerated by the firmware,
and if a graphical framebuffer is exposed by a PCI device, its base
address and size are exposed to the OS via the Graphics Output
Protocol (GOP).

On arm64 PCI systems, the entire PCI hierarchy is reconfigured from
scratch at boot. This may result in the GOP framebuffer address to
become stale, if the BAR covering the framebuffer is modified. This
will cause the framebuffer to become unresponsive, and may in some
cases result in unpredictable behavior if the range is reassigned to
another device.

So add a quirk to the EFI fb driver to find the BAR associated with
the GOP base address, and set the IORESOURCE_PCI_FIXED attribute so
that the PCI core will leave it alone.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
As it turns out, setting the IORESOURCE_PCI_FIXED flag is not sufficient
to make the PCI core leave the BARs alone, so instead, the BAR resource
is claimed in the quirk handler.

As suggested by Lorenzo, a check is added that the device has memory
decoding enabled, and if it doesn't, no attempt is made to use the
EFI framebuffer.

 drivers/video/fbdev/efifb.c | 58 +++++++++++++++++++-
 1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
index 8c4dc1e1f94f..eeeaf78c4a5b 100644
--- a/drivers/video/fbdev/efifb.c
+++ b/drivers/video/fbdev/efifb.c
@@ -10,6 +10,7 @@
 #include <linux/efi.h>
 #include <linux/errno.h>
 #include <linux/fb.h>
+#include <linux/pci.h>
 #include <linux/platform_device.h>
 #include <linux/screen_info.h>
 #include <video/vga.h>
@@ -143,6 +144,9 @@ static struct attribute *efifb_attrs[] = {
 };
 ATTRIBUTE_GROUPS(efifb);
 
+static bool pci_bar_found;	/* did we find a BAR matching the efifb base? */
+static bool pci_bar_disabled;	/* was it disabled? */
+
 static int efifb_probe(struct platform_device *dev)
 {
 	struct fb_info *info;
@@ -152,7 +156,7 @@ static int efifb_probe(struct platform_device *dev)
 	unsigned int size_total;
 	char *option = NULL;
 
-	if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI)
+	if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI || pci_bar_disabled)
 		return -ENODEV;
 
 	if (fb_get_options("efifb", &option))
@@ -360,3 +364,55 @@ static struct platform_driver efifb_driver = {
 };
 
 builtin_platform_driver(efifb_driver);
+
+static void claim_efifb_bar(struct pci_dev *dev, int idx)
+{
+	u16 word;
+
+	pci_bar_found = true;
+
+	if (pci_claim_resource(dev, idx)) {
+		pci_bar_disabled = true;
+		dev_err(&dev->dev, "BAR %d: failed to claim efifb BAR\n", idx);
+		return;
+	}
+
+	pci_read_config_word(dev, PCI_COMMAND, &word);
+	if (!(word & PCI_COMMAND_MEMORY)) {
+		pci_bar_disabled = true;
+		dev_err(&dev->dev,
+			"BAR %d: efifb BAR has memory decoding disabled!\n", idx);
+		return;
+	}
+
+	dev_info(&dev->dev, "BAR %d: claimed for efifb\n", idx);
+}
+
+static void efifb_fixup_resources(struct pci_dev *dev)
+{
+	u64 base = screen_info.lfb_base;
+	u64 size = screen_info.lfb_size;
+	int i;
+
+	if (pci_bar_found || screen_info.orig_video_isVGA != VIDEO_TYPE_EFI)
+		return;
+
+	if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
+		base |= (u64)screen_info.ext_lfb_base << 32;
+
+	if (!base)
+		return;
+
+	for (i = 0; i < PCI_STD_RESOURCE_END; i++) {
+		struct resource *res = &dev->resource[i];
+
+		if (!(res->flags & IORESOURCE_MEM))
+			continue;
+
+		if (res->start <= base && res->end >= base + size - 1) {
+			claim_efifb_bar(dev, i);
+			break;
+		}
+	}
+}
+DECLARE_PCI_FIXUP_HEADER(PCI_ANY_ID, PCI_ANY_ID, efifb_fixup_resources);
-- 
2.7.4