Commit 62a0d98a authored by Benjamin Gaignard's avatar Benjamin Gaignard Committed by Daniel Vetter
Browse files

drm: allow to use mmuless SoC 



Some SoC without MMU have display driver where a drm/kms driver
could be implemented.

Before doing such kind of thing drm/kms must allow to use mmuless devices.
This patch propose to remove MMU configuration flag and add a cma helper
function to help implementing mmuless display driver

version 4:
- add documentation about drm_gem_cma_get_unmapped_area()
- stub it MMU case

Signed-off-by: default avatarBenjamin Gaignard <benjamin.gaignard@linaro.org>
[danvet: Use recommended struct member references in kernel-doc.]
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1483521177-21794-4-git-send-email-benjamin.gaignard@linaro.org
parent 99c48e1e

Documentation/gpu/drm-mm.rst

+11 −0
Original line number Diff line number Diff line
@@ -310,6 +310,17 @@ created. 
Drivers that want to map the GEM object upfront instead of handling page

faults can implement their own mmap file operation handler.



For platforms without MMU the GEM core provides a helper method

:c:func:`drm_gem_cma_get_unmapped_area`. The mmap() routines will call

this to get a proposed address for the mapping.



To use :c:func:`drm_gem_cma_get_unmapped_area`, drivers must fill the

struct :c:type:`struct file_operations <file_operations>` get_unmapped_area

field with a pointer on :c:func:`drm_gem_cma_get_unmapped_area`.



More detailed information about get_unmapped_area can be found in

Documentation/nommu-mmap.txt



Memory Coherency

----------------

drivers/gpu/drm/Kconfig

+2 −2
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ 
#

menuconfig DRM

	tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"

	depends on (AGP || AGP=n) && !EMULATED_CMPXCHG && MMU && HAS_DMA

	depends on (AGP || AGP=n) && !EMULATED_CMPXCHG && HAS_DMA

	select HDMI

	select FB_CMDLINE

	select I2C
@@ -113,7 +113,7 @@ config DRM_LOAD_EDID_FIRMWARE 


config DRM_TTM

	tristate

	depends on DRM

	depends on DRM && MMU

	help

	  GPU memory management subsystem for devices with multiple

	  GPU memory types. Will be enabled automatically if a device driver

drivers/gpu/drm/drm_gem_cma_helper.c

+71 −0
Original line number Diff line number Diff line
@@ -358,6 +358,77 @@ int drm_gem_cma_mmap(struct file *filp, struct vm_area_struct *vma) 
}

EXPORT_SYMBOL_GPL(drm_gem_cma_mmap);



#ifndef CONFIG_MMU

/**

 * drm_gem_cma_get_unmapped_area - propose address for mapping in noMMU cases

 * @filp: file object

 * @addr: memory address

 * @len: buffer size

 * @pgoff: page offset

 * @flags: memory flags

 *

 * This function is used in noMMU platforms to propose address mapping

 * for a given buffer.

 * It's intended to be used as a direct handler for the struct

 * &file_operations.get_unmapped_area operation.

 *

 * Returns:

 * mapping address on success or a negative error code on failure.

 */

unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,

					    unsigned long addr,

					    unsigned long len,

					    unsigned long pgoff,

					    unsigned long flags)

{

	struct drm_gem_cma_object *cma_obj;

	struct drm_gem_object *obj = NULL;

	struct drm_file *priv = filp->private_data;

	struct drm_device *dev = priv->minor->dev;

	struct drm_vma_offset_node *node;



	if (drm_device_is_unplugged(dev))

		return -ENODEV;



	drm_vma_offset_lock_lookup(dev->vma_offset_manager);

	node = drm_vma_offset_exact_lookup_locked(dev->vma_offset_manager,

						  pgoff,

						  len >> PAGE_SHIFT);

	if (likely(node)) {

		obj = container_of(node, struct drm_gem_object, vma_node);

		/*

		 * When the object is being freed, after it hits 0-refcnt it

		 * proceeds to tear down the object. In the process it will

		 * attempt to remove the VMA offset and so acquire this

		 * mgr->vm_lock.  Therefore if we find an object with a 0-refcnt

		 * that matches our range, we know it is in the process of being

		 * destroyed and will be freed as soon as we release the lock -

		 * so we have to check for the 0-refcnted object and treat it as

		 * invalid.

		 */

		if (!kref_get_unless_zero(&obj->refcount))

			obj = NULL;

	}



	drm_vma_offset_unlock_lookup(dev->vma_offset_manager);



	if (!obj)

		return -EINVAL;



	if (!drm_vma_node_is_allowed(node, priv)) {

		drm_gem_object_unreference_unlocked(obj);

		return -EACCES;

	}



	cma_obj = to_drm_gem_cma_obj(obj);



	drm_gem_object_unreference_unlocked(obj);



	return cma_obj->vaddr ? (unsigned long)cma_obj->vaddr : -EINVAL;

}

EXPORT_SYMBOL_GPL(drm_gem_cma_get_unmapped_area);

#endif



#ifdef CONFIG_DEBUG_FS

/**

 * drm_gem_cma_describe - describe a CMA GEM object for debugfs

include/drm/drm_gem_cma_helper.h

+17 −0
Original line number Diff line number Diff line
@@ -53,6 +53,23 @@ struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm, 


extern const struct vm_operations_struct drm_gem_cma_vm_ops;



#ifndef CONFIG_MMU

unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,

					    unsigned long addr,

					    unsigned long len,

					    unsigned long pgoff,

					    unsigned long flags);

#else

static inline unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,

							  unsigned long addr,

							  unsigned long len,

							  unsigned long pgoff,

							  unsigned long flags)

{

	return -EINVAL;

}

#endif



#ifdef CONFIG_DEBUG_FS

void drm_gem_cma_describe(struct drm_gem_cma_object *obj, struct seq_file *m);

#endif

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