Re: [PATCH 8/9] drm: Add infrastructure for platform devices

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Jun 25, 2020 at 02:00:10PM +0200, Thomas Zimmermann wrote:
> Platform devices might operate on firmware framebuffers, such as VESA or
> EFI. Before a native driver for the graphics hardware can take over the
> device, it has to remove any platform driver that operates on the firmware
> framebuffer. Platform helpers provide the infrastructure for platform
> drivers to acquire firmware framebuffers, and for native drivers to remove
> them lateron.
> 
> It works similar to the related fbdev mechanism. During initialization, the
> platform driver acquires the firmware framebuffer's I/O memory and provides
> a callback to be removed. The native driver later uses this inforamtion to
> remove any platform driver for it's framebuffer I/O memory.
> 
> The platform helper's removal code is integrated into the existing code for
> removing conflicting fraembuffers, so native drivers use it automatically.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/Kconfig        |   6 ++
>  drivers/gpu/drm/Makefile       |   1 +
>  drivers/gpu/drm/drm_platform.c | 118 +++++++++++++++++++++++++++++++++
>  include/drm/drm_fb_helper.h    |  18 ++++-
>  include/drm/drm_platform.h     |  42 ++++++++++++
>  5 files changed, 184 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/gpu/drm/drm_platform.c
>  create mode 100644 include/drm/drm_platform.h
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index c4fd57d8b717..e9d6892f9d38 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -229,6 +229,12 @@ config DRM_SCHED
>  	tristate
>  	depends on DRM
>  
> +config DRM_PLATFORM_HELPER
> +	bool
> +	depends on DRM
> +	help
> +	  Helpers for DRM platform devices
> +
>  source "drivers/gpu/drm/i2c/Kconfig"
>  
>  source "drivers/gpu/drm/arm/Kconfig"
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 2c0e5a7e5953..8ceb21d0770a 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -32,6 +32,7 @@ drm-$(CONFIG_AGP) += drm_agpsupport.o
>  drm-$(CONFIG_PCI) += drm_pci.o
>  drm-$(CONFIG_DEBUG_FS) += drm_debugfs.o drm_debugfs_crc.o
>  drm-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
> +drm-$(CONFIG_DRM_PLATFORM_HELPER) += drm_platform.o
>  
>  drm_vram_helper-y := drm_gem_vram_helper.o
>  obj-$(CONFIG_DRM_VRAM_HELPER) += drm_vram_helper.o
> diff --git a/drivers/gpu/drm/drm_platform.c b/drivers/gpu/drm/drm_platform.c
> new file mode 100644
> index 000000000000..09a2f2a31aa5
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_platform.c
> @@ -0,0 +1,118 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +#include <drm/drm_drv.h>
> +#include <drm/drm_managed.h>
> +#include <drm/drm_platform.h>
> +
> +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 struct drm_aperture *
> +drm_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;
> +
> +	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 = drmm_kzalloc(dev, sizeof(*ap), GFP_KERNEL);

One technical thing here, but that'll be even more clear once the next
patch is using the driver core detach function: This should be devm_ not
drmm_ (both here and below) because it's tied to the lifetime of the
physical device and the driver binding.

Once the driver is unbound, even if drm_device keeps surviving because
userspace is still holding references, there's no point in trying to
unbind it again. So auto-cleanup using devm_ is the right thing here imo.

And with the change to the driver model unbind you will have a struct
device * pointer, so this all works out.
-Daniel

> +	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);
> +
> +	return ap;
> +}
> +
> +static void drm_aperture_release(struct drm_aperture *ap)
> +{
> +	bool kicked_out = ap->kicked_out;
> +
> +	if (!kicked_out)
> +		mutex_lock(&drm_apertures_lock);
> +
> +	list_del(&ap->lh);
> +	if (ap->funcs->release)
> +		ap->funcs->release(ap);
> +
> +	if (!kicked_out)
> +		mutex_unlock(&drm_apertures_lock);
> +}
> +
> +static void drm_aperture_acquire_release(struct drm_device *dev, void *ptr)
> +{
> +	struct drm_aperture *ap = ptr;
> +
> +	drm_aperture_release(ap);
> +}
> +
> +struct drm_aperture *
> +drmm_aperture_acquire(struct drm_device *dev,
> +		      resource_size_t base, resource_size_t size,
> +		      const struct drm_aperture_funcs *funcs)
> +{
> +	struct drm_aperture *ap;
> +	int ret;
> +
> +	ap = drm_aperture_acquire(dev, base, size, funcs);
> +	if (IS_ERR(ap))
> +		return ap;
> +	ret = drmm_add_action_or_reset(dev, drm_aperture_acquire_release, ap);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	return ap;
> +}
> +EXPORT_SYMBOL(drmm_aperture_acquire);
> +
> +void drm_kickout_apertures_at(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);
> +
> +		if (!overlap(base, end, ap->base, ap->base + ap->size))
> +			continue;
> +
> +		ap->kicked_out = true;
> +		if (ap->funcs->kickout)
> +			ap->funcs->kickout(ap);
> +		else
> +			drm_dev_put(ap->dev);
> +	}
> +
> +	mutex_unlock(&drm_apertures_lock);
> +}
> +EXPORT_SYMBOL(drm_kickout_apertures_at);
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 306aa3a60be9..a919b78b1961 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -35,7 +35,9 @@ struct drm_fb_helper;
>  #include <drm/drm_client.h>
>  #include <drm/drm_crtc.h>
>  #include <drm/drm_device.h>
> +#include <drm/drm_platform.h>
>  #include <linux/kgdb.h>
> +#include <linux/pci.h>
>  #include <linux/vgaarb.h>
>  
>  enum mode_set_atomic {
> @@ -465,6 +467,11 @@ 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_kickout_apertures_at(a->ranges[i].base, a->ranges[i].size);
> +
>  #if IS_REACHABLE(CONFIG_FB)
>  	return remove_conflicting_framebuffers(a, name, primary);
>  #else
> @@ -487,7 +494,16 @@ 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_kickout_apertures_at(base, size);
> +	}
>  
>  	/*
>  	 * WARNING: Apparently we must kick fbdev drivers before vgacon,
> diff --git a/include/drm/drm_platform.h b/include/drm/drm_platform.h
> new file mode 100644
> index 000000000000..475e88ee1fbd
> --- /dev/null
> +++ b/include/drm/drm_platform.h
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +
> +#ifndef _DRM_PLATFORM_H_
> +#define _DRM_PLATFORM_H_
> +
> +#include <linux/list.h>
> +#include <linux/types.h>
> +
> +struct drm_aperture;
> +struct drm_device;
> +
> +struct drm_aperture_funcs {
> +	void (*kickout)(struct drm_aperture *ap);
> +	void (*release)(struct drm_aperture *ap);
> +};
> +
> +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;
> +	bool kicked_out;
> +};
> +
> +struct drm_aperture *
> +drmm_aperture_acquire(struct drm_device *dev,
> +		      resource_size_t base, resource_size_t size,
> +		      const struct drm_aperture_funcs *funcs);
> +
> +#if defined (CONFIG_DRM_PLATFORM_HELPER)
> +void drm_kickout_apertures_at(resource_size_t base, resource_size_t size);
> +#else
> +static inline void
> +drm_kickout_apertures_at(resource_size_t base, resource_size_t size)
> +{
> +}
> +#endif
> +
> +#endif
> -- 
> 2.27.0
> 

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