[PATCH v3 2/2] fbdev: hyperv_fb: Allow graceful removal of framebuffer

[Saurabh Sengar <ssengar@linux.microsoft.com>]

When a Hyper-V framebuffer device is unbind, hyperv_fb driver tries to
release the framebuffer forcefully. If this framebuffer is in use it
produce the following WARN and hence this framebuffer is never released.

[   44.111220] WARNING: CPU: 35 PID: 1882 at drivers/video/fbdev/core/fb_info.c:70 framebuffer_release+0x2c/0x40
< snip >
[   44.111289] Call Trace:
[   44.111290]  <TASK>
[   44.111291]  ? show_regs+0x6c/0x80
[   44.111295]  ? __warn+0x8d/0x150
[   44.111298]  ? framebuffer_release+0x2c/0x40
[   44.111300]  ? report_bug+0x182/0x1b0
[   44.111303]  ? handle_bug+0x6e/0xb0
[   44.111306]  ? exc_invalid_op+0x18/0x80
[   44.111308]  ? asm_exc_invalid_op+0x1b/0x20
[   44.111311]  ? framebuffer_release+0x2c/0x40
[   44.111313]  ? hvfb_remove+0x86/0xa0 [hyperv_fb]
[   44.111315]  vmbus_remove+0x24/0x40 [hv_vmbus]
[   44.111323]  device_remove+0x40/0x80
[   44.111325]  device_release_driver_internal+0x20b/0x270
[   44.111327]  ? bus_find_device+0xb3/0xf0

Fix this by moving the release of framebuffer and assosiated memory
to fb_ops.fb_destroy function, so that framebuffer framework handles
it gracefully.

While we fix this, also replace manual registrations/unregistration of
framebuffer with devm_register_framebuffer.

Fixes: 68a2d20b79b1 ("drivers/video: add Hyper-V Synthetic Video Frame Buffer Driver")

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
---
[V3]
 - using simplified hvfb_putmem()

 drivers/video/fbdev/hyperv_fb.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index 09fb025477f7..76a42379c8df 100644
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -282,6 +282,8 @@ static uint screen_depth;
 static uint screen_fb_size;
 static uint dio_fb_size; /* FB size for deferred IO */
 
+static void hvfb_putmem(struct fb_info *info);
+
 /* Send message to Hyper-V host */
 static inline int synthvid_send(struct hv_device *hdev,
 				struct synthvid_msg *msg)
@@ -862,6 +864,17 @@ static void hvfb_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width,
 		hvfb_ondemand_refresh_throttle(par, x, y, width, height);
 }
 
+/*
+ * fb_ops.fb_destroy is called by the last put_fb_info() call at the end
+ * of unregister_framebuffer() or fb_release(). Do any cleanup related to
+ * framebuffer here.
+ */
+static void hvfb_destroy(struct fb_info *info)
+{
+	hvfb_putmem(info);
+	framebuffer_release(info);
+}
+
 /*
  * TODO: GEN1 codepaths allocate from system or DMA-able memory. Fix the
  *       driver to use the _SYSMEM_ or _DMAMEM_ helpers in these cases.
@@ -877,6 +890,7 @@ static const struct fb_ops hvfb_ops = {
 	.fb_set_par = hvfb_set_par,
 	.fb_setcolreg = hvfb_setcolreg,
 	.fb_blank = hvfb_blank,
+	.fb_destroy	= hvfb_destroy,
 };
 
 /* Get options from kernel paramenter "video=" */
@@ -1172,7 +1186,7 @@ static int hvfb_probe(struct hv_device *hdev,
 	if (ret)
 		goto error;
 
-	ret = register_framebuffer(info);
+	ret = devm_register_framebuffer(&hdev->device, info);
 	if (ret) {
 		pr_err("Unable to register framebuffer\n");
 		goto error;
@@ -1220,14 +1234,10 @@ static void hvfb_remove(struct hv_device *hdev)
 
 	fb_deferred_io_cleanup(info);
 
-	unregister_framebuffer(info);
 	cancel_delayed_work_sync(&par->dwork);
 
 	vmbus_close(hdev->channel);
 	hv_set_drvdata(hdev, NULL);
-
-	hvfb_putmem(info);
-	framebuffer_release(info);
 }
 
 static int hvfb_suspend(struct hv_device *hdev)
-- 
2.43.0