Re: [PATCH v4 4/4] drm: allow to use mmuless SoC

On Wed, Dec 07, 2016 at 11:06:51AM +0100, Benjamin Gaignard wrote:

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: Benjamin Gaignard benjamin.gaignard@linaro.org

Shouldn't we also update DRM_FB_HELPER_DEFAULT_OPS? With that addressed this all looks good to me. -Daniel

---

Documentation/gpu/drm-mm.rst | 11 ++++++ drivers/gpu/drm/Kconfig | 4 +-- drivers/gpu/drm/drm_gem_cma_helper.c | 69 ++++++++++++++++++++++++++++++++++++ include/drm/drm_gem_cma_helper.h | 17 +++++++++ 4 files changed, 99 insertions(+), 2 deletions(-)

diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst index bca8085..6e7efab 100644 --- a/Documentation/gpu/drm-mm.rst +++ b/Documentation/gpu/drm-mm.rst @@ -303,6 +303,17 @@ 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 GEM care 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

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 83ac815..0eae4ad 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -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

@@ -98,7 +98,7 @@ 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

diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c index 1d6c335..01016b1 100644 --- a/drivers/gpu/drm/drm_gem_cma_helper.c +++ b/drivers/gpu/drm/drm_gem_cma_helper.c @@ -358,6 +358,75 @@ 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.
• • 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

diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h index acd6af8..180b586 100644 --- a/include/drm/drm_gem_cma_helper.h +++ b/include/drm/drm_gem_cma_helper.h @@ -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 +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

1.9.1