linux-kernel - Re: [PATCH 3/5] drm: Add and export function drm_gem_cma_mmap

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Date:   Tue, 08 Dec 2020 14:00:22 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>, od@...c.me,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] drm: Add and export function

 drm_gem_cma_mmap_noncoherent

Hi Christoph,

Le mar. 3 nov. 2020 à 19:13, Paul Cercueil <paul@...pouillou.net> a 
écrit :
> Hi Christoph,
> 
> Le mar. 3 nov. 2020 à 18:50, Christoph Hellwig <hch@...radead.org> a 
> écrit :
>> On Mon, Nov 02, 2020 at 10:06:49PM +0000, Paul Cercueil wrote:
>>>  This function can be used by drivers that need to mmap dumb buffers
>>>  created with non-coherent backing memory.
>>> 
>>>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>>  ---
>>>   drivers/gpu/drm/drm_gem_cma_helper.c | 39 
>>> ++++++++++++++++++++++++++++
>>>   include/drm/drm_gem_cma_helper.h     |  2 ++
>>>   2 files changed, 41 insertions(+)
>>> 
>>>  diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c 
>>> b/drivers/gpu/drm/drm_gem_cma_helper.c
>>>  index 3bdd67795e20..4ed63f4896bd 100644
>>>  --- a/drivers/gpu/drm/drm_gem_cma_helper.c
>>>  +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
>>>  @@ -387,6 +387,45 @@ int drm_gem_cma_mmap(struct file *filp, 
>>> struct vm_area_struct *vma)
>>>   }
>>>   EXPORT_SYMBOL_GPL(drm_gem_cma_mmap);
>>> 
>>>  +/**
>>>  + * drm_gem_cma_mmap_noncoherent - memory-map a CMA GEM object with
>>>  + *     non-coherent cache attribute
>>>  + * @filp: file object
>>>  + * @vma: VMA for the area to be mapped
>>>  + *
>>>  + * Just like drm_gem_cma_mmap, but for a GEM object backed by 
>>> non-coherent
>>>  + * memory.
>>>  + *
>>>  + * Returns:
>>>  + * 0 on success or a negative error code on failure.
>>>  + */
>>>  +int drm_gem_cma_mmap_noncoherent(struct file *filp, struct 
>>> vm_area_struct *vma)
>>>  +{
>>>  +	struct drm_gem_cma_object *cma_obj;
>>>  +	int ret;
>>>  +
>>>  +	ret = drm_gem_mmap(filp, vma);
>>>  +	if (ret)
>>>  +		return ret;
>>>  +
>>>  +	cma_obj = to_drm_gem_cma_obj(vma->vm_private_data);
>>>  +
>>>  +	/*
>>>  +	 * Clear the VM_PFNMAP flag that was set by drm_gem_mmap(), and 
>>> set the
>>>  +	 * vm_pgoff (used as a fake buffer offset by DRM) to 0 as we 
>>> want to map
>>>  +	 * the whole buffer.
>>>  +	 */
>>>  +	vma->vm_flags &= ~VM_PFNMAP;
>>>  +	vma->vm_pgoff = 0;
>>>  +	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>>>  +
>>>  +	return remap_pfn_range(vma, vma->vm_start,
>>>  +			       cma_obj->paddr >> PAGE_SHIFT,
>>>  +			       vma->vm_end - vma->vm_start,
>>>  +			       vma->vm_page_prot);
>> 
>> Per patch 1 cma_obj->paddr is the dma address, while remap_pfn_range
>> expects a physical address.  This does not work.
> 
> Ok, what would be the correct way to mmap_noncoherent?

Waiting for your input here :)

Cheers,
-Paul