Date:	Wed, 18 Dec 2013 12:39:12 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: cirrusdrmfb broken with simplefb

At Wed, 18 Dec 2013 11:21:46 +0100,
David Herrmann wrote:
> 
> Hi
> 
> On Wed, Dec 18, 2013 at 11:17 AM, Takashi Iwai <tiwai@...e.de> wrote:
> > At Wed, 18 Dec 2013 09:44:35 +0100,
> > Takashi Iwai wrote:
> >>
> >> At Wed, 18 Dec 2013 09:21:28 +0100,
> >> David Herrmann wrote:
> >> >
> >> > Hi
> >> >
> >> > On Wed, Dec 18, 2013 at 8:42 AM, Takashi Iwai <tiwai@...e.de> wrote:
> >> > > Hi,
> >> > >
> >> > > with the recent enablement of simplefb on x86, cirrusdrmfb on QEMU/KVM
> >> > > gets broken now, as reported at:
> >> > >     https://bugzilla.novell.com/show_bug.cgi?id=855821
> >> > >
> >> > > The cirrus VGA resource is reserved at first as "BOOTFB" in
> >> > > arch/x86/kernel/sysfb_simplefb.c, which is taken by simplefb platform
> >> > > device.  This resource is, however, never released until the platform
> >> > > device is destroyed, and the framebuffer switching doesn't trigger
> >> > > it.  It calls fb's destroy callback, at most.  Then, cirrus driver
> >> > > tries to assign the resource, fails and gives up, resulting in a
> >> > > complete blank screen.
> >> > >
> >> > > The same problem should exist on other KMS drivers like mgag200 or
> >> > > ast, not only cirrus.  Intel graphics doesn't hit this problem just
> >> > > because the reserved iomem by BOOTFB isn't required by i915 driver.
> >> > >
> >> > > The patch below is a quick attempt to solve the issue.  It adds a new
> >> > > API function for releasing resources of platform_device, and call it
> >> > > in destroy op of simplefb.  But, forcibly releasing resources of a
> >> > > parent device doesn't sound like a correct design.  We may take such
> >> > > as a band aid, but definitely need a more fundamental fix.
> >> > >
> >> > > Any thoughts?
> >> >
> >> > That bug always existed, simplefb is just the first driver to hit it
> >> > (vesafb/efifb didn't use resources).
> >>
> >> Heh, the bug didn't "exist" because no other grabbed the resource
> >> before.  The way the cirrus driver allocates the resource is no bug,
> >> per se.  But the proper resource takeover is missing.
> >>
> >> > I'm aware of the issue but as a
> >> > workaround you can simply disable CONFIG_X86_SYSFB. That restores the
> >> > old behavior.
> >>
> >> Yes, but CONFIG_X86_SYSFB breaks things as of now.  Shouldn't it be
> >> mentioned or give some kconfig hints instead of silently giving a
> >> broken output, if any quick fix isn't possible?
> >>
> >> > As a proper fix, I'd propose something like:
> >> >   dev = platform_find_device("platform-framebuffer");
> >> >   platform_remove_device(dev);
> >> >
> >> > And we wrap this as:
> >> >   sysfb_remove_framebuffers()
> >> > in arch/x86/kernel/sysfb.c
> >> >
> >> > This should cause a ->remove() event for the platform-driver and
> >> > correctly release the resources. Comments?
> >>
> >> Who will call this?  From destroy callback?
> >> Or can we simply do put_device() the bound platform device instead?
> >
> > Just tested, put_device() doesn't work since the refcount isn't 1, so
> > if any, we need to call platform_device_unregister() to release
> > forcibly.
> >
> > The patch below seems working at a quick test.  But I still have
> > some bad feeling for unregistering the parent device from the child's
> > destroy callback...
> 
> The idea is right, but call it from
> "remove_conflicting_framebuffers()". The problem is, if we load a
> driver on top of a dummy like vesafb/efifb/simplefb, we never removed
> them properly. Instead, we only unregistered their fb driver. But with
> the driver-model, that's just removing the driver, not the dummy
> device.
> 
> So we'd just call platform_device_unregister() in
> remove_conflicting_framebuffers() instead of unregister_framebuffer()
> on such devices. I'm now at home and will have a look.

So, make sysfb_remove_framebuffers() available on all archs and
call it there?  Hmm...  I think we need a better binding between
platform_device and framebuffer device.  Maybe better than killing
a parent device, but IMO, the root cause is rather that we have two 
individual devices (platform and framebuffer) unnecessarily.  Can we
sort this out?

In anyway, the patch below is a quick revisited fix.  It's calling
sysfb_remove_framebuffers().  Instead of finding over a platform name
string as you suggested, the patch just tries to remember the
instance.

The ifdef in fbmem.c looks ugly, but we can clean up such a thing
later.  And, yes, the patch should be split.


thanks,

Takashi

---
diff --git a/arch/x86/include/asm/sysfb.h b/arch/x86/include/asm/sysfb.h
index 2aeb3e2..94ba0e4 100644
--- a/arch/x86/include/asm/sysfb.h
+++ b/arch/x86/include/asm/sysfb.h
@@ -76,8 +76,9 @@ static inline void sysfb_apply_efi_quirks(void)
 
 bool parse_mode(const struct screen_info *si,
 		struct simplefb_platform_data *mode);
-int create_simplefb(const struct screen_info *si,
+struct platform_device *create_simplefb(const struct screen_info *si,
 		    const struct simplefb_platform_data *mode);
+void sysfb_remove_framebuffers(void);
 
 #else /* CONFIG_X86_SYSFB */
 
@@ -87,10 +88,10 @@ static inline bool parse_mode(const struct screen_info *si,
 	return false;
 }
 
-static inline int create_simplefb(const struct screen_info *si,
+static inline struct platform_device *create_simplefb(const struct screen_info *si,
 				  const struct simplefb_platform_data *mode)
 {
-	return -EINVAL;
+	return ERR_PTR(-EINVAL);
 }
 
 #endif /* CONFIG_X86_SYSFB */
diff --git a/arch/x86/kernel/sysfb.c b/arch/x86/kernel/sysfb.c
index 193ec2c..4faa5d0 100644
--- a/arch/x86/kernel/sysfb.c
+++ b/arch/x86/kernel/sysfb.c
@@ -38,23 +38,22 @@
 #include <linux/screen_info.h>
 #include <asm/sysfb.h>
 
+static struct platform_device *pd;
+
 static __init int sysfb_init(void)
 {
 	struct screen_info *si = &screen_info;
 	struct simplefb_platform_data mode;
-	struct platform_device *pd;
 	const char *name;
 	bool compatible;
-	int ret;
 
 	sysfb_apply_efi_quirks();
 
 	/* try to create a simple-framebuffer device */
 	compatible = parse_mode(si, &mode);
 	if (compatible) {
-		ret = create_simplefb(si, &mode);
-		if (!ret)
-			return 0;
+		pd = create_simplefb(si, &mode);
+		return IS_ERR(pd) ? PTR_ERR(pd) : 0;
 	}
 
 	/* if the FB is incompatible, create a legacy framebuffer device */
@@ -70,5 +69,14 @@ static __init int sysfb_init(void)
 	return IS_ERR(pd) ? PTR_ERR(pd) : 0;
 }
 
+void sysfb_remove_framebuffers(void)
+{
+	if (!IS_ERR_OR_NULL(pd)) {
+		platform_device_unregister(pd);
+		pd = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(sysfb_remove_framebuffers);
+
 /* must execute after PCI subsystem for EFI quirks */
 device_initcall(sysfb_init);
diff --git a/arch/x86/kernel/sysfb_simplefb.c b/arch/x86/kernel/sysfb_simplefb.c
index 86179d4..d90042ac 100644
--- a/arch/x86/kernel/sysfb_simplefb.c
+++ b/arch/x86/kernel/sysfb_simplefb.c
@@ -61,10 +61,9 @@ __init bool parse_mode(const struct screen_info *si,
 	return false;
 }
 
-__init int create_simplefb(const struct screen_info *si,
+__init struct platform_device *create_simplefb(const struct screen_info *si,
 			   const struct simplefb_platform_data *mode)
 {
-	struct platform_device *pd;
 	struct resource res;
 	unsigned long len;
 
@@ -74,7 +73,7 @@ __init int create_simplefb(const struct screen_info *si,
 	len = PAGE_ALIGN(len);
 	if (len > (u64)si->lfb_size << 16) {
 		printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	/* setup IORESOURCE_MEM as framebuffer memory */
@@ -84,12 +83,8 @@ __init int create_simplefb(const struct screen_info *si,
 	res.start = si->lfb_base;
 	res.end = si->lfb_base + len - 1;
 	if (res.end <= res.start)
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 
-	pd = platform_device_register_resndata(NULL, "simple-framebuffer", 0,
+	return platform_device_register_resndata(NULL, "simple-framebuffer", 0,
 					       &res, 1, mode, sizeof(*mode));
-	if (IS_ERR(pd))
-		return PTR_ERR(pd);
-
-	return 0;
 }
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 010d191..49b0f89 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -34,6 +34,9 @@
 #include <linux/fb.h>
 
 #include <asm/fb.h>
+#ifdef CONFIG_X86
+#include <asm/sysfb.h>
+#endif
 
 
     /*
@@ -1600,6 +1603,9 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
 			       "%s vs %s - removing generic driver\n",
 			       name, registered_fb[i]->fix.id);
 			do_unregister_framebuffer(registered_fb[i]);
+#ifdef CONFIG_X86
+			sysfb_remove_framebuffers();
+#endif
 		}
 	}
 }
diff --git a/drivers/video/simplefb.c b/drivers/video/simplefb.c
index 210f3a0..c825b88 100644
--- a/drivers/video/simplefb.c
+++ b/drivers/video/simplefb.c
@@ -41,6 +41,11 @@ static struct fb_var_screeninfo simplefb_var = {
 	.vmode		= FB_VMODE_NONINTERLACED,
 };
 
+struct simplefb_priv {
+	u32 pseudo_palette[16];
+	bool fb_registered;
+};
+
 static int simplefb_setcolreg(u_int regno, u_int red, u_int green, u_int blue,
 			      u_int transp, struct fb_info *info)
 {
@@ -68,8 +73,11 @@ static int simplefb_setcolreg(u_int regno, u_int red, u_int green, u_int blue,
 
 static void simplefb_destroy(struct fb_info *info)
 {
+	struct simplefb_priv *priv = info->par;
+
 	if (info->screen_base)
 		iounmap(info->screen_base);
+	priv->fb_registered = false;
 }
 
 static struct fb_ops simplefb_ops = {
@@ -169,6 +177,7 @@ static int simplefb_probe(struct platform_device *pdev)
 	struct simplefb_params params;
 	struct fb_info *info;
 	struct resource *mem;
+	struct simplefb_priv *priv;
 
 	if (fb_get_options("simplefb", NULL))
 		return -ENODEV;
@@ -188,7 +197,7 @@ static int simplefb_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	info = framebuffer_alloc(sizeof(u32) * 16, &pdev->dev);
+	info = framebuffer_alloc(sizeof(struct simplefb_priv), &pdev->dev);
 	if (!info)
 		return -ENOMEM;
 	platform_set_drvdata(pdev, info);
@@ -225,7 +234,9 @@ static int simplefb_probe(struct platform_device *pdev)
 		framebuffer_release(info);
 		return -ENODEV;
 	}
-	info->pseudo_palette = (void *)(info + 1);
+
+	priv = info->par;
+	info->pseudo_palette = priv->pseudo_palette;
 
 	dev_info(&pdev->dev, "framebuffer at 0x%lx, 0x%x bytes, mapped to 0x%p\n",
 			     info->fix.smem_start, info->fix.smem_len,
@@ -243,6 +254,7 @@ static int simplefb_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	priv->fb_registered = true;
 	dev_info(&pdev->dev, "fb%d: simplefb registered!\n", info->node);
 
 	return 0;
@@ -251,8 +263,11 @@ static int simplefb_probe(struct platform_device *pdev)
 static int simplefb_remove(struct platform_device *pdev)
 {
 	struct fb_info *info = platform_get_drvdata(pdev);
+	struct simplefb_priv *priv = info->par;
+
+	if (priv->fb_registered)
+		unregister_framebuffer(info);
 
-	unregister_framebuffer(info);
 	framebuffer_release(info);
 
 	return 0;
--
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