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

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Message-Id: <JPBTPQ.TL10VUKPUBL23@crapouillou.net>
Date:   Thu, 11 Mar 2021 16:12:55 +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



Le jeu. 11 mars 2021 à 12:36, Christoph Hellwig <hch@...radead.org> a 
écrit :
> On Thu, Mar 11, 2021 at 12:32:27PM +0000, Paul Cercueil wrote:
>>  > 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?
> 
> You don't - you get it from using virt_to_page on the pointer returned
> from dma_alloc_noncoherent.  That beind said to keep the API sane I
> should probably add a wrapper that does that for you.

I tested using:

ret = dma_mmap_pages(cma_obj->base.dev->dev,
                     vma, vma->vm_end - vma->vm_start,
                     virt_to_page(cma_obj->vaddr));

It works fine.

I think I can use remap_pfn_range() for now, and switch to your new API 
once it's available in drm-misc-next.

Cheers,
-Paul