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@xxxxxxxxxx>
---
Documentation/gpu/drm-mm.rst | 11 ++++++
drivers/gpu/drm/Kconfig | 4 +-
drivers/gpu/drm/drm_gem_cma_helper.c | 71 ++++++++++++++++++++++++++++++++++++
include/drm/drm_gem_cma_helper.h | 17 +++++++++
4 files changed, 101 insertions(+), 2 deletions(-)
diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst
index bca8085..9d4aa11 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 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
----------------
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..19908bb 100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -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
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
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