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Date:   Thu, 11 Mar 2021 12:26:42 +0000
From:   Christoph Hellwig <hch@infradead.org>
To:     Paul Cercueil <paul@crapouillou.net>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Sam Ravnborg <sam@ravnborg.org>, od@zcrc.me,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        linux-mips@vger.kernel.org
Subject: Re: [PATCH v2 3/5] drm: Add and export function
 drm_gem_cma_mmap_noncoherent
Message-ID: <20210311122642.GB1739082@infradead.org>
References: <20210307202835.253907-1-paul@crapouillou.net>
 <20210307202835.253907-4-paul@crapouillou.net>
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> +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.