[PATCH v3] efifb: avoid reconfiguration of BAR that covers the framebuffer

[Bjorn Helgaas]

Hi Gary,

Thanks for the question.

On Wed, May 03, 2017 at 11:09:51AM +0800, Heyi Guo wrote:
> Hi Ard,
> 
> I have one comment inclined.
> 
> 
> 在 3/22/2017 11:30 PM, Ard Biesheuvel 写道:
> >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.
> >
> >Cc: Matt Fleming <matt at codeblueprint.co.uk>
> >Cc: Peter Jones <pjones at redhat.com>
> >Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> >---
> >v3: check device is enabled before attempting to claim the resource
> >
> >  drivers/video/fbdev/efifb.c | 60 +++++++++++++++++++-
> >  1 file changed, 59 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
> >index 8c4dc1e1f94f..88f653864a01 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_dev_disabled;	/* was the device 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_dev_disabled)
> >  		return -ENODEV;
> >  	if (fb_get_options("efifb", &option))
> >@@ -360,3 +364,57 @@ 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;
> >+
> >+	pci_read_config_word(dev, PCI_COMMAND, &word);
> >+	if (!(word & PCI_COMMAND_MEMORY)) {
> >+		pci_dev_disabled = true;
> >+		dev_err(&dev->dev,
> >+			"BAR %d: assigned to efifb but device is disabled!\n",
> >+			idx);
> >+		return;
> >+	}
> >+
> >+	if (pci_claim_resource(dev, idx)) {
> >+		pci_dev_disabled = true;
> >+		dev_err(&dev->dev,
> >+			"BAR %d: failed to claim resource for efifb!\n", idx);
> >+		return;
> >+	}
> >+
> >+	dev_info(&dev->dev, "BAR %d: assigned to 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) {
> Have we considered PCI address translation here? I suppose the
> address reported by EFI GOP should be the address of CPU domain, not
> address of PCI domain. Address read from PCI BAR is PCI address
> which should add translation offset before being compared to CPU
> domain address.

Every address in dev->resource[] is a CPU domain address, so address
translation offset should be handled correctly.

This is because __pci_read_base() calls pcibios_bus_to_resource() when
it fills in dev->resource[], and pcibios_bus_to_resource() applies any
host bridge address translation.

Bjorn