Re: [RFC v2 1/1] drm: allow to use mmuless SoC

On Wed, Nov 30, 2016 at 02:19:18PM +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 some cma helpers functions to help implementing mmuless display driver

version 2:

• define get_fb_unmapped_area() in drivers/video/fbdev/core/fbmem.c if HAVE_ARCH_FB_UNMAPPED_AREA is set and get_fb_unmapped_area not already defined in the architecture

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

drivers/gpu/drm/Kconfig | 4 +-- drivers/gpu/drm/drm_fb_cma_helper.c | 4 +++ drivers/gpu/drm/drm_gem_cma_helper.c | 62 ++++++++++++++++++++++++++++++++++++ drivers/gpu/drm/drm_vm.c | 4 +++ drivers/video/fbdev/core/fbmem.c | 15 +++++++++ include/drm/drm_gem_cma_helper.h | 6 ++++ 6 files changed, 93 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..b1414b6 100644 --- a/drivers/gpu/drm/drm_fb_cma_helper.c +++ b/drivers/gpu/drm/drm_fb_cma_helper.c @@ -343,8 +343,12 @@ 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 } static struct fb_ops drm_fbdev_cma_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

Ok, me asking for a separate helper was probably too much. The #ifdefs here are still ugly, but on 2nd thought this just looks like the dma api is broken on no-mmu? Shouldn't we instead have a patch somewhere which gives us a working dma_mmap_wc on nommu platforms?

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

Depending upon how it's used it might be better to stub it out ...

+#else +unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,

• 			    unsigned long addr,
  

• 			    unsigned long len,
  

• 			    unsigned long pgoff,
  

• 			    unsigned long flags)
  

With no user and no kerneldoc I kinda have no idea what this is even for. The name also doesn't help, it says "get_unmapped_area", but very clearly you're returning a kernel vaddr cast to a long (and with ERR_PTR semantics on top, but non-standard). Why is this not called get_vaddr? -Daniel

+{

• 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) { diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 76c1ad9..54488ee 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1492,6 +1492,21 @@ static long fb_compat_ioctl(struct file *file, unsigned int cmd, return 0; } +#if defined(HAVE_ARCH_FB_UNMAPPED_AREA) && !defined(get_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;

+} +#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..177a20d 100644 --- a/include/drm/drm_gem_cma_helper.h +++ b/include/drm/drm_gem_cma_helper.h @@ -53,6 +53,12 @@ struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm, extern const struct vm_operations_struct drm_gem_cma_vm_ops; +unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,

• 			     unsigned long addr,
  

• 			     unsigned long len,
  

• 			     unsigned long pgoff,
  

• 			     unsigned long flags);
  

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

#endif

1.9.1