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

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Message-Id: <FQI8JQ.KNVZ9XZ67ZV41@crapouillou.net>
Date:   Tue, 03 Nov 2020 19:13:27 +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 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?

-Paul