On Thu, Apr 15, 2021 at 08:56:20AM +0200, Thomas Zimmermann wrote:

Hi

Am 09.04.21 um 11:22 schrieb Daniel Vetter:

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Is it that easy? simepldrm's detach function has code to synchronize with
concurrent hotplug removals. If we can use drm_dev_unplug() for everything,
I'm all for it.

Uh, I should have looked at the code instead of just asking silly
questions :-)

Now I'm even more scared, and also more convinced that we're recreating

a

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bad version of some of the core driver model concepts.

I think the ideal option here would be if drm_aperture could unload
(unbind really) the platform driver for us, through the driver model. Then
there's only one place that keeps track whether the driver is unbound or
not. I'm not sure whether this can be done fully generic on a struct
device, or whether we need special code for each type. Since atm we only
have simpledrm we can just specialize on platform_device and it's good
enough.

I meanwhile found that calling platform_device_unregister() is the right
thing to do. It is like a hot-unplug event. It's simple to implement and
removes the generic device as well. Any memory ranges for the generic device
are gone as well. Only the native driver's native device will remain. That's
better than the existing simplefb driver.

That sounds great.

Which unregister function to call still driver-specific, so I kept the
callback.

Could we have the callback in core code, and you do something like
drm_aperture_acquire_platform (and later on drm_aperture_acquire_pci or
whatever, although tbh I'm not sure we ever get anything else than
platform). That function can do a runtime check that drm_device->dev is
actually a platform dev.

Another idea: Do the runtime casting in the core without anything? Atm we
have platform that needs support, maybe pci device, so we could easily
extend this and just let it do the right thing. Then no callback is
needed. I.e.

	if (is_platform_dev(drm_device->dev))
		platform_device_unregister(drm_device->dev);
	else
		WARN(1, "not yet implemented\n");

or something like that.

I just find the callback to essentially unregister a device a bit
redundant.
-Daniel

Best regards
Thomas

quoted

I think best here would be to Cc: gregkh on this patch and the simpledrm
->detach implementatation, and ask for his feedback as driver model
maintainer. Maybe if you could hack together the platform_device unbind
path as proof of concept would be even better.

Either way, this is really tricky.
-Daniel

quoted

Best regards
Thomas

quoted

Or maybe we should tie this more into the struct device mode and force an
unload that way? That way devm cleanup would work as one expects, and
avoid the need for anything specific (hopefully) in this detach callback.

Just feels a bit like we're reinventing half of the driver model here,
badly.

quoted

+ *	};
+ *
+ *	static int acquire_framebuffers(struct drm_device *dev, struct pci_dev *pdev)
+ *	{
+ *		resource_size_t start, len;
+ *		struct drm_aperture *ap;
+ *
+ *		base = pci_resource_start(pdev, 0);
+ *		size = pci_resource_len(pdev, 0);
+ *
+ *		ap = devm_acquire_aperture(dev, base, size, &ap_funcs);
+ *		if (IS_ERR(ap))
+ *			return PTR_ERR(ap);
+ *
+ *		return 0;
+ *	}
+ *
+ *	static int probe(struct pci_dev *pdev)
+ *	{
+ *		struct drm_device *dev;
+ *		int ret;
+ *
+ *		// ... Initialize the device...
+ *		dev = devm_drm_dev_alloc();
+ *		...
+ *
+ *		// ... and acquire ownership of the framebuffer.
+ *		ret = acquire_framebuffers(dev, pdev);
+ *		if (ret)
+ *			return ret;
+ *
+ *		drm_dev_register();
+ *
+ *		return 0;
+ *	}
+ *
+ * The generic driver is now subject to forced removal by other drivers. This
+ * is when the detach function in struct &drm_aperture_funcs comes into play.
+ * When a driver calls drm_fb_helper_remove_conflicting_framebuffers() et al
+ * for the registered framebuffer range, the DRM core calls struct
+ * &drm_aperture_funcs.detach and the generic driver has to onload itself. It
+ * may not access the device's registers, framebuffer memory, ROM, etc after
+ * detach returned. If the driver supports hotplugging, detach can be treated
+ * like an unplug event.
+ *
+ * .. code-block:: c
+ *
+ *	static void detach_from_device(struct drm_device *dev,
+ *				       resource_size_t base,
+ *				       resource_size_t size)
+ *	{
+ *		// Signal unplug
+ *		drm_dev_unplug(dev);
+ *
+ *		// Maybe do other clean-up operations
+ *		...
+ *	}
+ *
+ *	static struct drm_aperture_funcs ap_funcs = {
+ *		.detach = detach_from_device,
+ *	};
+ */
+
+/**
+ * struct drm_aperture - Represents a DRM framebuffer aperture
+ *
+ * This structure has no public fields.
+ */
+struct drm_aperture {
+	struct drm_device *dev;
+	resource_size_t base;
+	resource_size_t size;
+
+	const struct drm_aperture_funcs *funcs;
+
+	struct list_head lh;
+};
+
+static LIST_HEAD(drm_apertures);
+
+static DEFINE_MUTEX(drm_apertures_lock);
+
+static bool overlap(resource_size_t base1, resource_size_t end1,
+		    resource_size_t base2, resource_size_t end2)
+{
+	return (base1 < end2) && (end1 > base2);
+}
+
+static void devm_aperture_acquire_release(void *data)
+{
+	struct drm_aperture *ap = data;
+	bool detached = !ap->dev;
+
+	if (!detached)

Uh this needs a comment that if ap->dev is NULL then we're called from
drm_aperture_detach_drivers() and hence the lock is already held.

quoted

+		mutex_lock(&drm_apertures_lock);

and an

	else
		locdep_assert_held(&drm_apertures_lock);

here to check that. I was scratching my head first quite a bit how you'd
solve the deadlock, this is a neat solution (much simpler than anything I
came up with in my head). But needs comments.

quoted

+
+	list_del(&ap->lh);
+
+	if (!detached)
+		mutex_unlock(&drm_apertures_lock);
+}
+
+/**
+ * devm_aperture_acquire - Acquires ownership of a framebuffer on behalf of a DRM driver.
+ * @dev:	the DRM device to own the framebuffer memory
+ * @base:	the framebuffer's byte offset in physical memory
+ * @size:	the framebuffer size in bytes
+ * @funcs:	callback functions
+ *
+ * Installs the given device as the new owner. The function fails if the
+ * framebuffer range, or parts of it, is currently owned by
another

driver.

quoted

quoted

quoted

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+ * To evict current owners, callers should use
+ * drm_fb_helper_remove_conflicting_framebuffers() et al. before calling this
+ * function. Acquired apertures are released automatically if the underlying
+ * device goes away.
+ *
+ * Returns:
+ * An instance of struct &drm_aperture on success, or a pointer-encoded
+ * errno value otherwise.
+ */
+struct drm_aperture *
+devm_aperture_acquire(struct drm_device *dev,
+		      resource_size_t base, resource_size_t size,
+		      const struct drm_aperture_funcs *funcs)
+{
+	size_t end = base + size;
+	struct list_head *pos;
+	struct drm_aperture *ap;
+	int ret;
+
+	mutex_lock(&drm_apertures_lock);
+
+	list_for_each(pos, &drm_apertures) {
+		ap = container_of(pos, struct drm_aperture, lh);
+		if (overlap(base, end, ap->base, ap->base + ap->size))
+			return ERR_PTR(-EBUSY);
+	}
+
+	ap = devm_kzalloc(dev->dev, sizeof(*ap), GFP_KERNEL);
+	if (!ap)
+		return ERR_PTR(-ENOMEM);
+
+	ap->dev = dev;
+	ap->base = base;
+	ap->size = size;
+	ap->funcs = funcs;
+	INIT_LIST_HEAD(&ap->lh);
+
+	list_add(&ap->lh, &drm_apertures);
+
+	mutex_unlock(&drm_apertures_lock);
+
+	ret = devm_add_action_or_reset(dev->dev, devm_aperture_acquire_release, ap);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return ap;
+}
+EXPORT_SYMBOL(devm_aperture_acquire);
+
+void drm_aperture_detach_drivers(resource_size_t base, resource_size_t size)
+{
+	resource_size_t end = base + size;
+	struct list_head *pos, *n;
+
+	mutex_lock(&drm_apertures_lock);
+
+	list_for_each_safe(pos, n, &drm_apertures) {
+		struct drm_aperture *ap =
+			container_of(pos, struct drm_aperture, lh);
+		struct drm_device *dev = ap->dev;
+
+		if (!overlap(base, end, ap->base, ap->base + ap->size))
+			continue;
+
+		ap->dev = NULL; /* detach from device */
+		if (drm_WARN_ON(dev, !ap->funcs->detach))
+			continue;
+		ap->funcs->detach(dev, ap->base, ap->size);
+	}
+
+	mutex_unlock(&drm_apertures_lock);
+}
+EXPORT_SYMBOL(drm_aperture_detach_drivers);

Is this just exported because of the inline functions in the
headers?

Imo

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better to make them proper functions (they're big after your patch&not
perf critical, so not good candidates for inlining anyway).

quoted

diff --git a/include/drm/drm_aperture.h b/include/drm/drm_aperture.h
index 13766efe9517..696cec75ef78 100644
--- a/include/drm/drm_aperture.h
+++ b/include/drm/drm_aperture.h

@@ -4,8 +4,30 @@
   #define _DRM_APERTURE_H_
   #include <linux/fb.h>
+#include <linux/pci.h>
   #include <linux/vgaarb.h>
+struct drm_aperture;
+struct drm_device;
+
+struct drm_aperture_funcs {
+	void (*detach)(struct drm_device *dev, resource_size_t base, resource_size_t size);
+};
+
+struct drm_aperture *
+devm_aperture_acquire(struct drm_device *dev,
+		      resource_size_t base, resource_size_t size,
+		      const struct drm_aperture_funcs *funcs);
+
+#if defined(CONFIG_DRM_APERTURE)
+void drm_aperture_detach_drivers(resource_size_t base, resource_size_t size);
+#else
+static inline void
+drm_aperture_detach_drivers(resource_size_t base, resource_size_t size)
+{
+}
+#endif
+
   /**
    * drm_fb_helper_remove_conflicting_framebuffers - remove firmware-configured framebuffers
    * @a: memory range, users of which are to be removed

@@ -20,6 +42,11 @@ static inline int
   drm_fb_helper_remove_conflicting_framebuffers(struct apertures_struct *a,
   					      const char *name, bool primary)
   {
+	int i;
+
+	for (i = 0; i < a->count; ++i)
+		drm_aperture_detach_drivers(a->ranges[i].base, a->ranges[i].size);
+
   #if IS_REACHABLE(CONFIG_FB)
   	return remove_conflicting_framebuffers(a, name, primary);
   #else

@@ -43,7 +70,16 @@ static inline int
   drm_fb_helper_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
   						  const char *name)
   {
-	int ret = 0;
+	resource_size_t base, size;
+	int bar, ret = 0;
+
+	for (bar = 0; bar < PCI_STD_NUM_BARS; bar++) {
+		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
+			continue;
+		base = pci_resource_start(pdev, bar);
+		size = pci_resource_len(pdev, bar);
+		drm_aperture_detach_drivers(base, size);
+	}
   	/*
   	 * WARNING: Apparently we must kick fbdev drivers before vgacon,

-- 
2.30.1

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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