Re: [RFC 1/1] drm: allow to use mmuless SoC

2016-11-30 14:52 GMT+01:00 Daniel Vetter daniel@ffwll.ch:

On Wed, Nov 30, 2016 at 12:21:24PM +0100, Benjamin Gaignard wrote:

...

Some platforms without MMU have display drivers where a drm/kms driver could be implemented. Before doing such kind of thing drm/kms must allow to use mmuless devices. This patch proposes to remove MMU configuration flag and add some cma helpers functions to help implementing mmuless display driver

Signed-off-by: Benjamin Gaignard benjamin.gaignard@linaro.org

drivers/gpu/drm/Kconfig | 4 +-- drivers/gpu/drm/drm_fb_cma_helper.c | 20 ++++++++++++ drivers/gpu/drm/drm_gem_cma_helper.c | 62 ++++++++++++++++++++++++++++++++++++

Hacking this into cma helpers feels very wrong to me. mmu-less looks like it works substantially differently enough that it warrants a new set of mmu-less gem helpers. And maybe that will showcase more code-refactoring opportunities between cma helpers, mmu-less helpers and shmem-based gem objects. And if there's none, then I think copypasting is better than ending up in a mess.

Only the 2 calls to dma_mmap_wc() are problematic within ARM nommu architecture. After Laurent remarks I have move get_fb_unmapped_area() to fbmem.c it really limits the modifications in cma helpers...

...

drivers/gpu/drm/drm_vm.c | 4 +++ drivers/video/fbdev/core/fbmem.c | 8 +++++ include/drm/drm_gem_cma_helper.h | 6 ++++ 6 files changed, 102 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 8d9cf73..36c102b 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_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c index 81b3558..a3cef79 100644 --- a/drivers/gpu/drm/drm_fb_cma_helper.c +++ b/drivers/gpu/drm/drm_fb_cma_helper.c @@ -343,10 +343,30 @@ int drm_fb_cma_debugfs_show(struct seq_file *m, void *arg)

static int drm_fb_cma_mmap(struct fb_info *info, struct vm_area_struct *vma) { +#ifdef CONFIG_MMU return dma_mmap_writecombine(info->device, vma, info->screen_base, info->fix.smem_start, info->fix.smem_len); +#else

• return vm_iomap_memory(vma, vma->vm_start, info->fix.smem_len);
  

+#endif }

+#ifdef HAVE_ARCH_FB_UNMAPPED_AREA +unsigned long get_fb_unmapped_area(struct file *filp,

•                            unsigned long addr, unsigned long len,
  

•                            unsigned long pgoff, unsigned long flags)
  

+{

• struct fb_info * const info = filp->private_data;
  

• unsigned long fb_size = PAGE_ALIGN(info->fix.smem_len);
  

• if (pgoff > fb_size || len > fb_size - pgoff)
  

•         return -EINVAL;
  

• return (unsigned long)info->screen_base + pgoff;
  

+} +EXPORT_SYMBOL_GPL(get_fb_unmapped_area); +#endif

static struct fb_ops drm_fbdev_cma_ops = { .owner = THIS_MODULE, DRM_FB_HELPER_DEFAULT_OPS, diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c index 1d6c335..de13535 100644 --- a/drivers/gpu/drm/drm_gem_cma_helper.c +++ b/drivers/gpu/drm/drm_gem_cma_helper.c @@ -318,11 +318,16 @@ static int drm_gem_cma_mmap_obj(struct drm_gem_cma_object *cma_obj, vma->vm_flags &= ~VM_PFNMAP; vma->vm_pgoff = 0;

+#ifdef CONFIG_MMU ret = dma_mmap_wc(cma_obj->base.dev->dev, vma, cma_obj->vaddr, cma_obj->paddr, vma->vm_end - vma->vm_start); if (ret) drm_gem_vm_close(vma);

+#else

• ret = vm_iomap_memory(vma, vma->vm_start,
  

•                       (vma->vm_end - vma->vm_start));
  

+#endif return ret; }

@@ -358,6 +363,63 @@ int drm_gem_cma_mmap(struct file *filp, struct vm_area_struct *vma) } EXPORT_SYMBOL_GPL(drm_gem_cma_mmap);

+#ifdef CONFIG_MMU +#define drm_gem_cma_get_unmapped_area NULL +#else +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;
  

+} +#endif +EXPORT_SYMBOL_GPL(drm_gem_cma_get_unmapped_area);

#ifdef CONFIG_DEBUG_FS /**

• drm_gem_cma_describe - describe a CMA GEM object for debugfs

diff --git a/drivers/gpu/drm/drm_vm.c b/drivers/gpu/drm/drm_vm.c index caa4e4c..974e02b 100644 --- a/drivers/gpu/drm/drm_vm.c +++ b/drivers/gpu/drm/drm_vm.c @@ -489,6 +489,7 @@ static int drm_mmap_dma(struct file *filp, struct vm_area_struct *vma) #if defined(__i386__) || defined(__x86_64__) pgprot_val(vma->vm_page_prot) &= ~_PAGE_RW; #else +#ifdef CONFIG_MMU /* Ye gads this is ugly. With more thought we could move this up higher and use `protection_map' instead. */ @@ -497,6 +498,7 @@ static int drm_mmap_dma(struct file *filp, struct vm_area_struct *vma) (pte_wrprotect (__pte(pgprot_val(vma->vm_page_prot))))); #endif +#endif }

  vma->vm_ops = &drm_vm_dma_ops;

@@ -573,6 +575,7 @@ static int drm_mmap_locked(struct file *filp, struct vm_area_struct *vma) #if defined(__i386__) || defined(__x86_64__) pgprot_val(vma->vm_page_prot) &= ~_PAGE_RW; #else +#ifdef CONFIG_MMU /* Ye gads this is ugly. With more thought we could move this up higher and use `protection_map' instead. */ @@ -581,6 +584,7 @@ static int drm_mmap_locked(struct file *filp, struct vm_area_struct *vma) (pte_wrprotect (__pte(pgprot_val(vma->vm_page_prot))))); #endif +#endif }

  switch (map->type) {

drm_vm.c is a legacy horror show. Instead of hacking even more garbage into this, can't we just not compile this for MMU-less platforms? A bunch of stubs in drm_internal.h is all that should be needed for this, since on MMU-less you should never be able to enable one of the legacy drivers which need the exported symbols from this file.

Following your advice I have removed drm_vm.c from the build if CONFIG_MMU is not set I only had to stub drm_legacy_vma_flush() to compile. I will include that in v3

Cheers, Daniel

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diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 76c1ad9..d6a83bd 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1492,6 +1492,14 @@ static long fb_compat_ioctl(struct file *file, unsigned int cmd, return 0; }

+#ifdef HAVE_ARCH_FB_UNMAPPED_AREA +extern unsigned long get_fb_unmapped_area(struct file *filp,

•                                   unsigned long addr,
  

•                                   unsigned long len,
  

•                                   unsigned long pgoff,
  

•                                   unsigned long flags);
  

+#endif

static const struct file_operations fb_fops = { .owner = THIS_MODULE, .read = fb_read, diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h index acd6af8..79e9dbd 100644 --- a/include/drm/drm_gem_cma_helper.h +++ b/include/drm/drm_gem_cma_helper.h @@ -51,6 +51,12 @@ int drm_gem_cma_dumb_map_offset(struct drm_file *file_priv, struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm, size_t size);

+unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,

•                                     unsigned long addr,
  

•                                     unsigned long len,
  

•                                     unsigned long pgoff,
  

•                                     unsigned long flags);
  

extern const struct vm_operations_struct drm_gem_cma_vm_ops;

#ifdef CONFIG_DEBUG_FS

1.9.1

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