firmware: coreboot: Don't register a pdev if screen_info data is present

On coreboot platforms, a system framebuffer may be provided to the Linux
kernel by filling a LB_TAG_FRAMEBUFFER entry in the coreboot table. But
a coreboot payload (e.g: SeaBIOS) could also provide its own framebuffer
information to the Linux kernel.

If that's the case, arch x86 boot code will fill the global screen_info
data and this used by the Generic System Framebuffers (sysfb) framework,
to register a platform device with pdata about the system's framebuffer.

But later, the framebuffer_coreboot driver will try to do the same and
attempt to register a "simple-framebuffer" platform device (using the
information from the coreboot table), which will lead to an error due a
device with the same name already being registered:

    sysfs: cannot create duplicate filename '/bus/platform/devices/simple-framebuffer.0'
    ...
    coreboot: could not register framebuffer
    framebuffer coreboot8: probe with driver framebuffer failed with error -17

To prevent this issue, make the framebuffer_core driver to not register
a platform device if the global struct screen_info data has been filled.

Reported-by: Brian Norris <briannorris@chromium.org>
Closes: https://lore.kernel.org/all/ZuCG-DggNThuF4pj@b20ea791c01f/T/#ma7fb65acbc1a56042258adac910992bb225a20d2
Suggested-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Link: https://lore.kernel.org/r/20240916110040.1688511-3-javierm@redhat.com
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

diff --git a/drivers/firmware/google/framebuffer-coreboot.c b/drivers/firmware/google/framebuffer-coreboot.c
index daadd71d8ddd371a4596c3039746eeb38b01f04d..c68c9f56370f28c6ae01dec6372528d53929cdda 100644 (file)
--- a/drivers/firmware/google/framebuffer-coreboot.c
+++ b/drivers/firmware/google/framebuffer-coreboot.c
@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/platform_data/simplefb.h>
 #include <linux/platform_device.h>
+#include <linux/sysfb.h>
 
 #include "coreboot_table.h"
 
@@ -36,6 +37,19 @@ static int framebuffer_probe(struct coreboot_device *dev)
                .format = NULL,
        };
 
+       /*
+        * On coreboot systems, the advertised LB_TAG_FRAMEBUFFER entry
+        * in the coreboot table should only be used if the payload did
+        * not pass a framebuffer information to the Linux kernel.
+        *
+        * If the global screen_info data has been filled, the Generic
+        * System Framebuffers (sysfb) will already register a platform
+        * device and pass that screen_info as platform_data to a driver
+        * that can scan-out using the system provided framebuffer.
+        */
+       if (sysfb_handles_screen_info())
+               return -ENODEV;
+
        if (!fb->physical_address)
                return -ENODEV;