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 12:36:42 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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

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.