// SPDX-License-Identifier: MIT

#include <linux/device.h>
#include <linux/fb.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/pci.h>
#include <linux/platform_device.h> /* for firmware helpers */
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/vgaarb.h>

#include <drm/drm_aperture.h>
#include <drm/drm_drv.h>
#include <drm/drm_print.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. DRM aperture functions manage
 * ownership of DRM framebuffer memory and hand-over between drivers.
 *
 * DRM drivers should call drm_aperture_remove_conflicting_framebuffers()
 * at the top of their probe function. The function removes any generic
 * driver that is currently associated with the given framebuffer memory.
 * If the framebuffer is located at PCI BAR 0, the rsp code looks as in the
 * example given below.
 *
 * .. code-block:: c
 *
 *      static const struct drm_driver example_driver = {
 *              ...
 *      };
 *
 *      static int remove_conflicting_framebuffers(struct pci_dev *pdev)
 *      {
 *              bool primary = false;
 *              resource_size_t base, size;
 *              int ret;
 *
 *              base = pci_resource_start(pdev, 0);
 *              size = pci_resource_len(pdev, 0);
 *      #ifdef CONFIG_X86
 *              primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
 *      #endif
 *
 *              return drm_aperture_remove_conflicting_framebuffers(base, size, primary,
 *                                                                  &example_driver);
 *      }
 *
 *      static int probe(struct pci_dev *pdev)
 *      {
 *              int ret;
 *
 *              // Remove any generic drivers...
 *              ret = remove_conflicting_framebuffers(pdev);
 *              if (ret)
 *                      return ret;
 *
 *              // ... and initialize the hardware.
 *              ...
 *
 *              drm_dev_register();
 *
 *              return 0;
 *      }
 *
 * PCI device drivers should call
 * drm_aperture_remove_conflicting_pci_framebuffers() and let it detect the
 * framebuffer apertures automatically. Device drivers without knowledge of
 * the framebuffer's location shall call drm_aperture_remove_framebuffers(),
 * which removes all drivers for known framebuffer.
 *
 * 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
 * given framebuffer memory. Ownership of the framebuffer memory is achieved
 * by calling devm_aperture_acquire_from_firmware(). On success, the driver
 * is the owner of the framebuffer range. The function fails if the
 * framebuffer is already by another driver. See below for an example.
 *
 * .. code-block:: c
 *
 *      static int acquire_framebuffers(struct drm_device *dev, struct platform_device *pdev)
 *      {
 *              resource_size_t base, size;
 *
 *              mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 *              if (!mem)
 *                      return -EINVAL;
 *              base = mem->start;
 *              size = resource_size(mem);
 *
 *              return devm_acquire_aperture_from_firmware(dev, base, size);
 *      }
 *
 *      static int probe(struct platform_device *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(dev, 0);
 *
 *              return 0;
 *      }
 *
 * The generic driver is now subject to forced removal by other drivers. This
 * only works for platform drivers that support hot unplug.
 * When a driver calls drm_aperture_remove_conflicting_framebuffers() et al
 * for the registered framebuffer range, the aperture helpers call
 * platform_device_unregister() and the generic driver unloads itself. It
 * may not access the device's registers, framebuffer memory, ROM, etc
 * afterwards.
 */

struct drm_aperture {
        struct drm_device *dev;
        resource_size_t base;
        resource_size_t size;
        struct list_head lh;
        void (*detach)(struct drm_device *dev);
};

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)
                return;

        mutex_lock(&drm_apertures_lock);
        list_del(&ap->lh);
        mutex_unlock(&drm_apertures_lock);
}

static int devm_aperture_acquire(struct drm_device *dev,
                                 resource_size_t base, resource_size_t size,
                                 void (*detach)(struct drm_device *))
{
        size_t end = base + size;
        struct list_head *pos;
        struct drm_aperture *ap;

        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)) {
                        mutex_unlock(&drm_apertures_lock);
                        return -EBUSY;
                }
        }

        ap = devm_kzalloc(dev->dev, sizeof(*ap), GFP_KERNEL);
        if (!ap) {
                mutex_unlock(&drm_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, &drm_apertures);

        mutex_unlock(&drm_apertures_lock);

        return devm_add_action_or_reset(dev->dev, devm_aperture_acquire_release, ap);
}

static void drm_aperture_detach_firmware(struct drm_device *dev)
{
        struct platform_device *pdev = to_platform_device(dev->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_from_firmware - Acquires ownership of a firmware 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
 *
 * Installs the given device as the new owner of the framebuffer. The function
 * expects the framebuffer to be provided by a platform device that has been
 * set up by firmware. Firmware can be any generic interface, such as EFI,
 * VESA, VGA, etc. If the native hardware driver takes over ownership of the
 * framebuffer range, the firmware state gets lost. Aperture helpers will then
 * unregister the platform device automatically. Acquired apertures are
 * released automatically if the underlying device goes away.
 *
 * The function fails if the framebuffer range, or parts of it, is currently
 * owned by another driver. To evict current owners, callers should use
 * drm_aperture_remove_conflicting_framebuffers() et al. before calling this
 * function. The function also fails if the given device is not a platform
 * device.
 *
 * Returns:
 * 0 on success, or a negative errno value otherwise.
 */
int devm_aperture_acquire_from_firmware(struct drm_device *dev, resource_size_t base,
                                        resource_size_t size)
{
        if (drm_WARN_ON(dev, !dev_is_platform(dev->dev)))
                return -EINVAL;

        return devm_aperture_acquire(dev, base, size, drm_aperture_detach_firmware);
}
EXPORT_SYMBOL(devm_aperture_acquire_from_firmware);

static 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 (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(&drm_apertures_lock);
}

/**
 * drm_aperture_remove_conflicting_framebuffers - remove existing framebuffers in the given range
 * @base: the aperture's base address in physical memory
 * @size: aperture size in bytes
 * @primary: also kick vga16fb if present
 * @req_driver: requesting DRM driver
 *
 * This function removes graphics device drivers which use memory range described by
 * @base and @size.
 *
 * Returns:
 * 0 on success, or a negative errno code otherwise
 */
int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_size_t size,
                                                 bool primary, const struct drm_driver *req_driver)
{
#if IS_REACHABLE(CONFIG_FB)
        struct apertures_struct *a;
        int ret;

        a = alloc_apertures(1);
        if (!a)
                return -ENOMEM;

        a->ranges[0].base = base;
        a->ranges[0].size = size;

        ret = remove_conflicting_framebuffers(a, req_driver->name, primary);
        kfree(a);

        if (ret)
                return ret;
#endif

        drm_aperture_detach_drivers(base, size);

        return 0;
}
EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);

/**
 * drm_aperture_remove_conflicting_pci_framebuffers - remove existing framebuffers for PCI devices
 * @pdev: PCI device
 * @req_driver: requesting DRM driver
 *
 * This function removes graphics device drivers using memory range configured
 * for any of @pdev's memory bars. The function assumes that PCI device with
 * shadowed ROM drives a primary display and so kicks out vga16fb.
 *
 * Returns:
 * 0 on success, or a negative errno code otherwise
 */
int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
                                                     const struct drm_driver *req_driver)
{
        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,
         * otherwise the vga fbdev driver falls over.
         */
#if IS_REACHABLE(CONFIG_FB)
        ret = remove_conflicting_pci_framebuffers(pdev, req_driver->name);
#endif
        if (ret == 0)
                ret = vga_remove_vgacon(pdev);
        return ret;
}
EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);