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Date: Thu, 11 Nov 2021 12:57:57 +0100
From: Javier Martinez Canillas <fmartine@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org,
Hans de Goede <hdegoede@...hat.com>,
Peter Jones <pjones@...hat.com>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Thomas Zimmermann <tzimmermann@...e.de>,
linux-fbdev@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
Ilya Trukhanov <lahvuun@...il.com>,
Thorsten Leemhuis <regressions@...mhuis.info>,
Javier Martinez Canillas <javierm@...hat.com>,
stable@...r.kernel.org, Borislav Petkov <bp@...e.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH v3] fbdev: Prevent probing generic drivers if a FB is already registered
The efifb and simplefb drivers just render to a pre-allocated frame buffer
and rely on the display hardware being initialized before the kernel boots.
But if another driver already probed correctly and registered a fbdev, the
generic drivers shouldn't be probed since an actual driver for the display
hardware is already present.
This is more likely to occur after commit d391c5827107 ("drivers/firmware:
move x86 Generic System Framebuffers support") since the "efi-framebuffer"
and "simple-framebuffer" platform devices are registered at a later time.
Link: https://lore.kernel.org/r/20211110200253.rfudkt3edbd3nsyj@lahvuun/
Fixes: d391c5827107 ("drivers/firmware: move x86 Generic System Framebuffers support")
Reported-by: Ilya Trukhanov <lahvuun@...il.com>
Cc: <stable@...r.kernel.org> # 5.15.x
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
---
Changes in v3:
- Cc <stable@...r.kernel.org> since a Fixes: tag is not enough (gregkh).
Changes in v2:
- Add a Link: tag with a reference to the bug report (Thorsten Leemhuis).
- Add a comment explaining why the probe fails earlier (Daniel Vetter).
- Add a Fixes: tag for stable to pick the fix (Daniel Vetter).
- Add Daniel Vetter's Reviewed-by: tag.
- Improve the commit message and mention the culprit commit
drivers/video/fbdev/efifb.c | 11 +++++++++++
drivers/video/fbdev/simplefb.c | 11 +++++++++++
2 files changed, 22 insertions(+)
diff --git drivers/video/fbdev/efifb.c drivers/video/fbdev/efifb.c
index edca3703b964..ea42ba6445b2 100644
--- drivers/video/fbdev/efifb.c
+++ drivers/video/fbdev/efifb.c
@@ -351,6 +351,17 @@ static int efifb_probe(struct platform_device *dev)
char *option = NULL;
efi_memory_desc_t md;
+ /*
+ * Generic drivers must not be registered if a framebuffer exists.
+ * If a native driver was probed, the display hardware was already
+ * taken and attempting to use the system framebuffer is dangerous.
+ */
+ if (num_registered_fb > 0) {
+ dev_err(&dev->dev,
+ "efifb: a framebuffer is already registered\n");
+ return -EINVAL;
+ }
+
if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI || pci_dev_disabled)
return -ENODEV;
diff --git drivers/video/fbdev/simplefb.c drivers/video/fbdev/simplefb.c
index 62f0ded70681..b63074fd892e 100644
--- drivers/video/fbdev/simplefb.c
+++ drivers/video/fbdev/simplefb.c
@@ -407,6 +407,17 @@ static int simplefb_probe(struct platform_device *pdev)
struct simplefb_par *par;
struct resource *mem;
+ /*
+ * Generic drivers must not be registered if a framebuffer exists.
+ * If a native driver was probed, the display hardware was already
+ * taken and attempting to use the system framebuffer is dangerous.
+ */
+ if (num_registered_fb > 0) {
+ dev_err(&pdev->dev,
+ "simplefb: a framebuffer is already registered\n");
+ return -EINVAL;
+ }
+
if (fb_get_options("simplefb", NULL))
return -ENODEV;
--
2.33.1
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