[PATCH v4 2/2] firmware: coreboot: Don't register a pdev if screen_info data is present

[Javier Martinez Canillas]

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

Changes in v4:
- Use a sysfb_handles_screen_info() helper instead of screen_info_video_type()
  to fix build errors on platforms that don't define a struct screen_info
  (Thomas Zimmermann).

Changes in v3:
- Fix coreboot spelling to be all in lowercase (Julius Werner).

Changes in v2:
- Declare the struct screen_info as constant variable (Thomas Zimmermann).
- Use screen_info_video_type() instead of checking the screen_info video
  types directly (Thomas Zimmermann).
- Fix missing "device" word in a comment (Brian Norris).
- Fix some mispellings in a comment (Brian Norris).
- Change error code returned from -EINVAL to -ENODEV (Brian Norris).

 drivers/firmware/google/framebuffer-coreboot.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/firmware/google/framebuffer-coreboot.c b/drivers/firmware/google/framebuffer-coreboot.c
index daadd71d8ddd..c68c9f56370f 100644
--- 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;
 
-- 
2.46.0