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

Daniel Vetter daniel at ffwll.ch
Thu Dec 1 06:56:34 UTC 2016


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 at 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
> 

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


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