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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Benjamin,

Thank you for the patch.

On Wednesday 30 Nov 2016 12:21:24 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 +++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_vm.c             |  4 +++

I'll let someone more knowledgeable than me comment on these two files.

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

[snip]

> 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

Shouldn't this be #ifndef ? When the symbol is defined the implementation is 
provided by the architecture.

By the way, given that you provide a generic implementation here, what's the 
reason some architecture need to implement the function in a special way ? 
Couldn't we come up with a generic implementation across all architectures ?

> +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);

Shouldn't this be defined somewhere in drivers/video/ instead, as the code is 
fbdev-specific and only used in drivers/video/fbdev/core/fbmem.c ?

> +#endif
> +
>  static struct fb_ops drm_fbdev_cma_ops = {
>  	.owner		= THIS_MODULE,
>  	DRM_FB_HELPER_DEFAULT_OPS,

[snip]

> 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

This should come from a header file.

>  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

-- 
Regards,

Laurent Pinchart

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