[Mesa-dev] [PATCH 2/4] DRI: Add DRIimage map and unmap functions

[Rob Herring]

On Mon, Apr 25, 2016 at 7:42 AM, Daniel Stone <daniel at fooishbar.org> wrote:
> Hi,
>
> On 22 April 2016 at 19:12, Eric Anholt <eric at anholt.net> wrote:
>> I think this needs a longer comment to explain what the interface does:
>>
>> "Returns a map of the specified region of a __DRIimage for the specified
>> usage.
>>
>> flags must always include __DRI_IMAGE_TRANSFER_READ and may include
>> __DRI_IMAGE_TRANSFER_WRITE if the mapping is written[*].  If
>> __DRI_IMAGE_TRANSFER_WRITE is not included, behavior when writing the
>> mapping is undefined.
>
> Hrm. Though the Gallium implementation currently forces READ, it seems
> like drivers requiring transfer would benefit from READ being
> optional, if it elides a copy of data which will just be overwritten
> anyway. How about:
> 'flags may include __DRI_IMAGE_TRANSFER_READ, which will populate the
> mapping with the current buffer content. If __DRI_IMAGE_TRANSFER_READ
> is not included in the flags, the buffer content at map time is
> undefined. Users wanting to modify the mapping must include
> __DRI_IMAGE_TRANSFER_WRITE; if __DRI_IMAGE_TRANSFER_WRITE is not
> included, behaviour when writing the mapping is undefined.'

Sounds good. I've made READ optional and added this text.

>
> Also, you're missing the footnote ... ?

Not sure what you mean here. Can you elaborate?

Rob