From:   Javier Martinez Canillas <javierm@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Sam Ravnborg <sam@ravnborg.org>, linux-fbdev@vger.kernel.org,
        dri-devel@lists.freedesktop.org,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Ilya Trukhanov <lahvuun@gmail.com>,
        Javier Martinez Canillas <javierm@redhat.com>
Subject: [PATCH] fbdev: Prevent probing generic drivers if a FB is already registered
Date:   Thu, 11 Nov 2021 10:20:53 +0100
Message-Id: <20211111092053.1328304-1-javierm@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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.

Reported-by: Ilya Trukhanov <lahvuun@gmail.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

 drivers/video/fbdev/efifb.c    | 6 ++++++
 drivers/video/fbdev/simplefb.c | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git drivers/video/fbdev/efifb.c drivers/video/fbdev/efifb.c
index edca3703b964..76325c07cf0c 100644
--- drivers/video/fbdev/efifb.c
+++ drivers/video/fbdev/efifb.c
@@ -351,6 +351,12 @@ static int efifb_probe(struct platform_device *dev)
 	char *option = NULL;
 	efi_memory_desc_t md;
 
+	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..55c1f54d7663 100644
--- drivers/video/fbdev/simplefb.c
+++ drivers/video/fbdev/simplefb.c
@@ -407,6 +407,12 @@ static int simplefb_probe(struct platform_device *pdev)
 	struct simplefb_par *par;
 	struct resource *mem;
 
+	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