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// SPDX-License-Identifier: MIT
#include <linux/aperture.h>
#include <linux/device.h>
#include <linux/fb.h> /* for old fbdev helpers */
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/pci.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/sysfb.h>
#include <linux/types.h>
#include <linux/vgaarb.h>
/**
* DOC: overview
*
* A graphics device might be supported by different drivers, but only one
* driver can be active at any given time. Many systems load a generic
* graphics drivers, such as EFI-GOP or VESA, early during the boot process.
* During later boot stages, they replace the generic driver with a dedicated,
* hardware-specific driver. To take over the device the dedicated driver
* first has to remove the generic driver. Aperture functions manage
* ownership of framebuffer memory and hand-over between drivers.
*
* Graphics drivers should call aperture_remove_conflicting_devices()
* at the top of their probe function. The function removes any generic
* driver that is currently associated with the given framebuffer memory.
* An example for a graphics device on the platform bus is shown below.
*
* .. code-block:: c
*
* static int example_probe(struct platform_device *pdev)
* {
* struct resource *mem;
* resource_size_t base, size;
* int ret;
*
* mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
* if (!mem)
* return -ENODEV;
* base = mem->start;
* size = resource_size(mem);
*
* ret = aperture_remove_conflicting_devices(base, size, false, "example");
* if (ret)
* return ret;
*
* // Initialize the hardware
* ...
*
* return 0;
* }
*
* static const struct platform_driver example_driver = {
* .probe = example_probe,
* ...
* };
*
* The given example reads the platform device's I/O-memory range from the
* device instance. An active framebuffer will be located within this range.
* The call to aperture_remove_conflicting_devices() releases drivers that
* have previously claimed ownership of the range and are currently driving
* output on the framebuffer. If successful, the new driver can take over
* the device.
*
* While the given example uses a platform device, the aperture helpers work
* with every bus that has an addressable framebuffer. In the case of PCI,
* device drivers can also call aperture_remove_conflicting_pci_devices() and
* let the function detect the apertures automatically. Device drivers without
* knowledge of the framebuffer's location can call
* aperture_remove_all_conflicting_devices(), which removes all known devices.
*
* Drivers that are susceptible to being removed by other drivers, such as
* generic EFI or VESA drivers, have to register themselves as owners of their
* framebuffer apertures. Ownership of the framebuffer memory is achieved
* by calling devm_aperture_acquire_for_platform_device(). If successful, the
* driveris the owner of the framebuffer range. The function fails if the
* framebuffer is already owned by another driver. See below for an example.
*
* .. code-block:: c
*
* static int generic_probe(struct platform_device *pdev)
* {
* struct resource *mem;
* resource_size_t base, size;
*
* mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
* if (!mem)
* return -ENODEV;
* base = mem->start;
* size = resource_size(mem);
*
* ret = devm_aperture_acquire_for_platform_device(pdev, base, size);
* if (ret)
* return ret;
*
* // Initialize the hardware
* ...
*
* return 0;
* }
*
* static int generic_remove(struct platform_device *)
* {
* // Hot-unplug the device
* ...
*
* return 0;
* }
*
* static const struct platform_driver generic_driver = {
* .probe = generic_probe,
* .remove = generic_remove,
* ...
* };
*
* The similar to the previous example, the generic driver claims ownership
* of the framebuffer memory from its probe function. This will fail if the
* memory range, or parts of it, is already owned by another driver.
*
* If successful, the generic driver is now subject to forced removal by
* another driver. This only works for platform drivers that support hot
* unplugging. When a driver calls aperture_remove_conflicting_devices()
* et al for the registered framebuffer range, the aperture helpers call
* platform_device_unregister() and the generic driver unloads itself. The
* generic driver also has to provide a remove function to make this work.
* Once hot unplugged fro mhardware, it may not access the device's
* registers, framebuffer memory, ROM, etc afterwards.
*/
struct aperture_range {
struct device *dev;
resource_size_t base;
resource_size_t size;
struct list_head lh;
void (*detach)(struct device *dev);
};
static LIST_HEAD(apertures);
static DEFINE_MUTEX(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 aperture_range *ap = data;
bool detached = !ap->dev;
if (detached)
return;
mutex_lock(&apertures_lock);
list_del(&ap->lh);
mutex_unlock(&apertures_lock);
}
static int devm_aperture_acquire(struct device *dev,
resource_size_t base, resource_size_t size,
void (*detach)(struct device *))
{
size_t end = base + size;
struct list_head *pos;
struct aperture_range *ap;
mutex_lock(&apertures_lock);
list_for_each(pos, &apertures) {
ap = container_of(pos, struct aperture_range, lh);
if (overlap(base, end, ap->base, ap->base + ap->size)) {
mutex_unlock(&apertures_lock);
return -EBUSY;
}
}
ap = devm_kzalloc(dev, sizeof(*ap), GFP_KERNEL);
if (!ap) {
mutex_unlock(&apertures_lock);
return -ENOMEM;
}
ap->dev = dev;
ap->base = base;
ap->size = size;
ap->detach = detach;
INIT_LIST_HEAD(&ap->lh);
list_add(&ap->lh, &apertures);
mutex_unlock(&apertures_lock);
return devm_add_action_or_reset(dev, devm_aperture_acquire_release, ap);
}
static void aperture_detach_platform_device(struct device *dev)
{
struct platform_device *pdev = to_platform_device(dev);
/*
* Remove the device from the device hierarchy. This is the right thing
* to do for firmware-based DRM drivers, such as EFI, VESA or VGA. After
* the new driver takes over the hardware, the firmware device's state
* will be lost.
*
* For non-platform devices, a new callback would be required.
*
* If the aperture helpers ever need to handle native drivers, this call
* would only have to unplug the DRM device, so that the hardware device
* stays around after detachment.
*/
platform_device_unregister(pdev);
}
/**
* devm_aperture_acquire_for_platform_device - Acquires ownership of an aperture
* on behalf of a platform device.
* @pdev: the platform device to own the aperture
* @base: the aperture's byte offset in physical memory
* @size: the aperture size in bytes
*
* Installs the given device as the new owner of the aperture. The function
* expects the aperture to be provided by a platform device. If another
* driver takes over ownership of the aperture, aperture helpers will then
* unregister the platform device automatically. All acquired apertures are
* released automatically when the underlying device goes away.
*
* The function fails if the aperture, or parts of it, is currently
* owned by another device. To evict current owners, callers should use
* remove_conflicting_devices() et al. before calling this function.
*
* Returns:
* 0 on success, or a negative errno value otherwise.
*/
int devm_aperture_acquire_for_platform_device(struct platform_device *pdev,
resource_size_t base,
resource_size_t size)
{
return devm_aperture_acquire(&pdev->dev, base, size, aperture_detach_platform_device);
}
EXPORT_SYMBOL(devm_aperture_acquire_for_platform_device);
static void aperture_detach_devices(resource_size_t base, resource_size_t size)
{
resource_size_t end = base + size;
struct list_head *pos, *n;
mutex_lock(&apertures_lock);
list_for_each_safe(pos, n, &apertures) {
struct aperture_range *ap = container_of(pos, struct aperture_range, lh);
struct device *dev = ap->dev;
if (WARN_ON_ONCE(!dev))
continue;
if (!overlap(base, end, ap->base, ap->base + ap->size))
continue;
ap->dev = NULL; /* detach from device */
list_del(&ap->lh);
ap->detach(dev);
}
mutex_unlock(&apertures_lock);
}
/**
* aperture_remove_conflicting_devices - remove devices in the given range
* @base: the aperture's base address in physical memory
* @size: aperture size in bytes
* @primary: also kick vga16fb if present; only relevant for VGA devices
* @name: a descriptive name of the requesting driver
*
* This function removes devices that own apertures within @base and @size.
*
* Returns:
* 0 on success, or a negative errno code otherwise
*/
int aperture_remove_conflicting_devices(resource_size_t base, resource_size_t size,
bool primary, const char *name)
{
#if IS_REACHABLE(CONFIG_FB)
struct apertures_struct *a;
int ret;
#endif
/*
* If a driver asked to unregister a platform device registered by
* sysfb, then can be assumed that this is a driver for a display
* that is set up by the system firmware and has a generic driver.
*
* Drivers for devices that don't have a generic driver will never
* ask for this, so let's assume that a real driver for the display
* was already probed and prevent sysfb to register devices later.
*/
sysfb_disable();
#if IS_REACHABLE(CONFIG_FB)
a = alloc_apertures(1);
if (!a)
return -ENOMEM;
a->ranges[0].base = base;
a->ranges[0].size = size;
ret = remove_conflicting_framebuffers(a, name, primary);
kfree(a);
if (ret)
return ret;
#endif
aperture_detach_devices(base, size);
return 0;
}
EXPORT_SYMBOL(aperture_remove_conflicting_devices);
/**
* aperture_remove_conflicting_pci_devices - remove existing framebuffers for PCI devices
* @pdev: PCI device
* @name: a descriptive name of the requesting driver
*
* This function removes devices that own apertures within any of @pdev's
* memory bars. The function assumes that PCI device with shadowed ROM
* drives a primary display and therefore kicks out vga16fb as well.
*
* Returns:
* 0 on success, or a negative errno code otherwise
*/
int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *name)
{
bool primary = false;
resource_size_t base, size;
int bar, ret;
#ifdef CONFIG_X86
primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
#endif
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);
ret = aperture_remove_conflicting_devices(base, size, primary, name);
if (ret)
break;
}
if (ret)
return ret;
/*
* WARNING: Apparently we must kick fbdev drivers before vgacon,
* otherwise the vga fbdev driver falls over.
*/
ret = vga_remove_vgacon(pdev);
if (ret)
return ret;
return 0;
}
EXPORT_SYMBOL(aperture_remove_conflicting_pci_devices);
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