linux-kernel - Re: [PATCH v2 3/5] drm: Add and export function drm_gem_cma_mmap

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Date:   Thu, 11 Mar 2021 12:32:27 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>, od@...c.me,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH v2 3/5] drm: Add and export function
 drm_gem_cma_mmap_noncoherent

Hi Christoph,

Le jeu. 11 mars 2021 à 12:26, Christoph Hellwig <hch@...radead.org> a 
écrit :
>>  +int drm_gem_cma_mmap_noncoherent(struct drm_gem_object *obj,
>>  +				 struct vm_area_struct *vma)
>>  +{
>>  +	struct drm_gem_cma_object *cma_obj;
>>  +	unsigned long pfn;
>>  +	int ret;
>>  +
>>  +	/*
>>  +	 * 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_pgoff -= drm_vma_node_start(&obj->vma_node);
>>  +	vma->vm_flags &= ~VM_PFNMAP;
>>  +	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>>  +
>>  +	cma_obj = to_drm_gem_cma_obj(obj);
>>  +
>>  +	pfn = PHYS_PFN(dma_to_phys(cma_obj->base.dev->dev, 
>> cma_obj->paddr));
>>  +
>>  +	ret = remap_pfn_range(vma, vma->vm_start, pfn,
>>  +			      vma->vm_end - vma->vm_start,
>>  +			      vma->vm_page_prot);
> 
> dma_to_phys must not be used by drivers.
> 
> I have a proper helper for this waiting for users:
> 
> http://git.infradead.org/users/hch/misc.git/commitdiff/96a546e7229ec53aadbdb7936d1e5e6cb5958952
> 
> If you can confirm the helpers works for you I can try to still sneak
> it to Linus for 5.12 to ease the merge pain.

I can try. How do I get a page pointer from a dma_addr_t?

-Paul