linux-kernel - Re: [PATCH v3.18-rc3] drm: msm: Allow exported dma-bufs to be mapped

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Message-ID: <CA+M3ks6SU6ivFPMbqWRsN0JLC3SBnkWJdRd+r_10n9qgpdbDCQ@mail.gmail.com>
Date:	Wed, 12 Nov 2014 10:41:16 +0100
From:	Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:	Rob Clark <robdclark@...il.com>
Cc:	Daniel Thompson <daniel.thompson@...aro.org>,
	David Airlie <airlied@...ux.ie>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	linaro-kernel@...ts.linaro.org,
	John Stultz <john.stultz@...aro.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Maarten Lankhorst <m.b.lankhorst@...il.com>
Subject: Re: [PATCH v3.18-rc3] drm: msm: Allow exported dma-bufs to be mapped

The same kind of issue has been fixed in v4l2:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/patch/drivers/media/v4l2-core/videobuf2-core.c?id=c1b96a236e94d49d9396d0bbceb5524519c5c66e

I'm ok to add a DRM_RDWR flag, just do not remove the code from sti
driver until I have been able to test it.

Benjamin


2014-11-11 17:26 GMT+01:00 Rob Clark <robdclark@...il.com>:
> On Tue, Nov 11, 2014 at 9:28 AM, Daniel Thompson
> <daniel.thompson@...aro.org> wrote:
>> On 10/11/14 17:36, Rob Clark wrote:
>>> On Mon, Nov 10, 2014 at 12:16 PM, Daniel Thompson
>>> <daniel.thompson@...aro.org> wrote:
>>>> diff --git a/drivers/gpu/drm/msm/msm_gem_prime.c b/drivers/gpu/drm/msm/msm_gem_prime.c
>>>> index ad772fe36115..4e4fa5828d5d 100644
>>>> --- a/drivers/gpu/drm/msm/msm_gem_prime.c
>>>> +++ b/drivers/gpu/drm/msm/msm_gem_prime.c
>>>> @@ -20,6 +20,14 @@
>>>>
>>>>  #include <linux/dma-buf.h>
>>>>
>>>> +struct dma_buf *msm_gem_prime_export(struct drm_device *dev,
>>>> +                                    struct drm_gem_object *obj, int flags)
>>>> +{
>>>> +       /* we want to be able to write in mmapped buffer */
>>>> +       flags |= O_RDWR;
>>>> +       return drm_gem_prime_export(dev, obj, flags);
>>>> +}
>>>> +
>>>
>>> seems like this probably should be done more centrally..  and in fact,
>>> might be better to have something like this in
>>> drm_prime_handle_to_fd_ioctl:
>>>
>>>     /* check flags are valid */
>>> -    if (args->flags & ~DRM_CLOEXEC)
>>> +    if (args->flags & ~(DRM_CLOEXEC | O_RDWR))
>>>        return -EINVAL;
>>>
>>> so exporter can specify whether to allow mmap or not.
>>
>> That makes sense I'll try this.
>>
>> Do we need to wrap O_RDWR in the same way we wrap O_CLOEXEC? (I don't
>> really understand why DRM_CLOEXEC exists; even the patch description
>> from when the symbol was introduced names it O_CLOEXEC).
>
> I *think* wrapping it w/ DRM_CLOEXEC was mostly just for purposes of
> making it clear which flags are appropriate.. probably best to do the
> same w/ a DRM_RDWR I guess
>
> BR,
> -R
>
>> Also the "flags |= O_RDWR" approach is copied from the sti driver. I'll
>> share a patch to remove it but that will definitely needs Benjamin's ack
>> because it will stop some userspaces working correctly (however I
>> suspect that Benjamin may be the only person currently with such a
>> userspace and that he can be persuaded not to call it a regression).
>>
>>
>> Daniel.



-- 
Benjamin Gaignard

Graphic Working Group

Linaro.org │ Open source software for ARM SoCs

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