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Subject: Re: [PATCH v2 2/3] drm: shmem: Add drm_gem_shmem_map_offset() wrapper
To:     Rob Herring <robh@kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        David Airlie <airlied@linux.ie>,
        Inki Dae <inki.dae@samsung.com>,
        Joonyoung Shim <jy0922.shim@samsung.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Kukjin Kim <kgene@kernel.org>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Sean Paul <sean@poorly.run>,
        Seung-Woo Kim <sw0312.kim@samsung.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <20190516141447.46839-1-steven.price@arm.com>
 <20190516141447.46839-3-steven.price@arm.com>
 <20190516202644.GE3851@phenom.ffwll.local>
From:   Steven Price <steven.price@arm.com>
Message-ID: <b4d04dfd-3f45-e456-e944-9c337a6538a5@arm.com>
Date:   Mon, 20 May 2019 10:21:09 +0100
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On 16/05/2019 21:26, Daniel Vetter wrote:
> On Thu, May 16, 2019 at 03:14:46PM +0100, Steven Price wrote:
>> Provide a wrapper for drm_gem_map_offset() for clients of shmem. This
>> wrapper provides the correct semantics for the drm_gem_shmem_mmap()
>> callback.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>  drivers/gpu/drm/drm_gem_shmem_helper.c | 20 ++++++++++++++++++++
>>  include/drm/drm_gem_shmem_helper.h     |  2 ++
>>  2 files changed, 22 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> index 1ee208c2c85e..9dbebc4897d1 100644
>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> @@ -400,6 +400,26 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
>>  }
>>  EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);
>>  
>> +/**
>> + * drm_gem_map_offset - return the fake mmap offset for a gem object
>> + * @file: drm file-private structure containing the gem object
>> + * @dev: corresponding drm_device
>> + * @handle: gem object handle
>> + * @offset: return location for the fake mmap offset
>> + *
>> + * This provides an offset suitable for user space to return to the
>> + * drm_gem_shmem_mmap() callback via an mmap() call.
>> + *
>> + * Returns:
>> + * 0 on success or a negative error code on failure.
>> + */
>> +int drm_gem_shmem_map_offset(struct drm_file *file, struct drm_device *dev,
>> +			     u32 handle, u64 *offset)
>> +{
>> +	return drm_gem_map_offset(file, dev, handle, offset);
>> +}
>> +EXPORT_SYMBOL_GPL(drm_gem_shmem_map_offset);
> 
> Not seeing the point of this mapper, since drm_gem_shmem_map_offset isn't
> speficic at all. It works for dumb, shmem, cma and private objects all
> equally well. I'd drop this and just directly call the underlying thing,
> no need to layer helpers.
> -Daniel

Ok, I'll drop it. I may have misunderstood, but I think Chris Wilson was
asking for it because shmem is the source of the particular requirements
of what can be mmap()d. But I think a helper can be added very easily if
anything changes, so this patch is probably premature.

I'll resend the series with this patch dropped.

Thanks,
Steve