linux-kernel - [PATCH] Fix failure of simpledrm probe when trying to grab FB from the EFI-based Framebuffer

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Date:   Sat, 11 Nov 2023 15:21:22 +1100
From:   Andrew Worsley <amworsley@...il.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org (open list:DRM DRIVER FOR FIRMWARE
        FRAMEBUFFERS), linux-kernel@...r.kernel.org (open list)
Cc:     Andrew Worsley <amworsley@...il.com>
Subject: [PATCH] Fix failure of simpledrm probe when trying to grab FB from the EFI-based Framebuffer

   The simpledrm.c does not call aperture_remove_conflicting_devices() in it's probe
   function as the drivers/video/aperture.c documentation says it should. Consequently
   it's request for the FB memory fails.

...
[    3.085302] simple-framebuffer bd58dc000.framebuffer: [drm] *ERROR* could not acquire memory range [??? 0xffff6e1d8629d580-0x2a5000001a7 flags 0x0]: -16
[    3.086433] simple-framebuffer: probe of bd58dc000.framebuffer failed with error -16
...

   In my case no driver provided /dev/dri/card0 device is available on boot up and X
   fails to start as per this from X start up log.

...
[     5.616] (WW) Falling back to old probe method for modesetting
[     5.616] (EE) open /dev/dri/card0: No such file or directory
...

   Fault confirmed and fixed on Asahi 6.5.0 kernel with both CONFIG_FB_EFI and
   CONFIG_DRM_SIMPLEDRM config options set.

Signed-off-by: Andrew Worsley <amworsley@...il.com>
---
 drivers/gpu/drm/tiny/simpledrm.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
index 5fefc895bca2..e55a536b04cf 100644
--- a/drivers/gpu/drm/tiny/simpledrm.c
+++ b/drivers/gpu/drm/tiny/simpledrm.c
@@ -8,6 +8,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_domain.h>
 #include <linux/regulator/consumer.h>
+#include <linux/aperture.h>
 
 #include <drm/drm_aperture.h>
 #include <drm/drm_atomic.h>
@@ -828,6 +829,13 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 	if (mem) {
 		void *screen_base;
 
+		ret = aperture_remove_conflicting_devices(mem->start, resource_size(mem),
+			DRIVER_NAME);
+		if (ret) {
+			drm_err(dev, "aperture_remove_conflicting_devices: failed:%d\n",
+			    __func__, ret);
+			return ERR_PTR(ret);
+		}
 		ret = devm_aperture_acquire_from_firmware(dev, mem->start, resource_size(mem));
 		if (ret) {
 			drm_err(dev, "could not acquire memory range %pr: %d\n", mem, ret);
@@ -848,6 +856,13 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 		if (!res)
 			return ERR_PTR(-EINVAL);
 
+		ret = aperture_remove_conflicting_devices(res->start, resource_size(res),
+			DRIVER_NAME);
+		if (ret) {
+			drm_err(dev, "aperture_remove_conflicting_devices: failed:%d\n",
+			    __func__, ret);
+			return ERR_PTR(ret);
+		}
 		ret = devm_aperture_acquire_from_firmware(dev, res->start, resource_size(res));
 		if (ret) {
 			drm_err(dev, "could not acquire memory range %pr: %d\n", res, ret);
-- 
2.42.0