linux-kernel - [PATCH] fbdev: efifb: do not load efifb if PCI BAR has changed but not fixuped

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Message-Id: <20250626094937.515552-1-oushixiong1025@163.com>
Date: Thu, 26 Jun 2025 17:49:37 +0800
From: oushixiong1025@....com
To: Helge Deller <deller@....de>
Cc: Peter Jones <pjones@...hat.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	linux-fbdev@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Shixiong Ou <oushixiong@...inos.cn>
Subject: [PATCH] fbdev: efifb: do not load efifb if PCI BAR has changed but not fixuped

From: Shixiong Ou <oushixiong@...inos.cn>

[WHY]
On an ARM machine, the following log is present:
[    0.900884] efifb: framebuffer at 0x1020000000, using 3072k, total 3072k
[    2.297884] amdgpu 0000:04:00.0: remove_conflicting_pci_framebuffers: bar 0: 0x1000000000 -> 0x100fffffff
[    2.297886] amdgpu 0000:04:00.0: remove_conflicting_pci_framebuffers: bar 2: 0x1010000000 -> 0x10101fffff
[    2.297888] amdgpu 0000:04:00.0: remove_conflicting_pci_framebuffers: bar 5: 0x58200000 -> 0x5823ffff

It show that the efifb framebuffer base is out of PCI BAR, and this
results in both efi-framebuffer and amdgpudrmfb co-existing.

The fbcon will be bound to efi-framebuffer by default and cannot be used.

[HOW]
Do not load efifb driver if PCI BAR has changed but not fixuped.
In the following cases:
	1. screen_info_lfb_pdev is NULL.
	2. __screen_info_relocation_is_valid return false.

Signed-off-by: Shixiong Ou <oushixiong@...inos.cn>
---
 drivers/video/fbdev/efifb.c     |  4 ++++
 drivers/video/screen_info_pci.c | 24 ++++++++++++++++++++++++
 include/linux/screen_info.h     |  5 +++++
 3 files changed, 33 insertions(+)

diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
index 0e1bd3dba255..de8d016c9a66 100644
--- a/drivers/video/fbdev/efifb.c
+++ b/drivers/video/fbdev/efifb.c
@@ -303,6 +303,10 @@ static void efifb_setup(struct screen_info *si, char *options)
 
 static inline bool fb_base_is_valid(struct screen_info *si)
 {
+	/* check whether fb_base has changed but not fixuped */
+	if (!screen_info_is_useful())
+		return false;
+
 	if (si->lfb_base)
 		return true;
 
diff --git a/drivers/video/screen_info_pci.c b/drivers/video/screen_info_pci.c
index 66bfc1d0a6dc..ac57dcaf0cac 100644
--- a/drivers/video/screen_info_pci.c
+++ b/drivers/video/screen_info_pci.c
@@ -9,6 +9,8 @@ static struct pci_dev *screen_info_lfb_pdev;
 static size_t screen_info_lfb_bar;
 static resource_size_t screen_info_lfb_res_start; // original start of resource
 static resource_size_t screen_info_lfb_offset; // framebuffer offset within resource
+static bool screen_info_changed;
+static bool screen_info_fixuped;
 
 static bool __screen_info_relocation_is_valid(const struct screen_info *si, struct resource *pr)
 {
@@ -24,6 +26,24 @@ static bool __screen_info_relocation_is_valid(const struct screen_info *si, stru
 	return true;
 }
 
+bool screen_info_is_useful(void)
+{
+	unsigned int type;
+	const struct screen_info *si = &screen_info;
+
+	type = screen_info_video_type(si);
+	if (type != VIDEO_TYPE_EFI)
+		return true;
+
+	if (screen_info_changed && !screen_info_fixuped) {
+		pr_warn("The screen_info has changed but not fixuped");
+		return false;
+	}
+
+	pr_info("The screen_info is useful");
+	return true;
+}
+
 void screen_info_apply_fixups(void)
 {
 	struct screen_info *si = &screen_info;
@@ -32,18 +52,22 @@ void screen_info_apply_fixups(void)
 		struct resource *pr = &screen_info_lfb_pdev->resource[screen_info_lfb_bar];
 
 		if (pr->start != screen_info_lfb_res_start) {
+			screen_info_changed = true;
 			if (__screen_info_relocation_is_valid(si, pr)) {
 				/*
 				 * Only update base if we have an actual
 				 * relocation to a valid I/O range.
 				 */
 				__screen_info_set_lfb_base(si, pr->start + screen_info_lfb_offset);
+				screen_info_fixuped = true;
 				pr_info("Relocating firmware framebuffer to offset %pa[d] within %pr\n",
 					&screen_info_lfb_offset, pr);
 			} else {
 				pr_warn("Invalid relocating, disabling firmware framebuffer\n");
 			}
 		}
+	} else {
+		screen_info_changed = true;
 	}
 }
 
diff --git a/include/linux/screen_info.h b/include/linux/screen_info.h
index 923d68e07679..632cdbb1adbe 100644
--- a/include/linux/screen_info.h
+++ b/include/linux/screen_info.h
@@ -138,9 +138,14 @@ ssize_t screen_info_resources(const struct screen_info *si, struct resource *r,
 u32 __screen_info_lfb_bits_per_pixel(const struct screen_info *si);
 
 #if defined(CONFIG_PCI)
+bool screen_info_is_useful(void);
 void screen_info_apply_fixups(void);
 struct pci_dev *screen_info_pci_dev(const struct screen_info *si);
 #else
+bool screen_info_is_useful(void)
+{
+	return true;
+}
 static inline void screen_info_apply_fixups(void)
 { }
 static inline struct pci_dev *screen_info_pci_dev(const struct screen_info *si)
-- 
2.25.1