about mmap dma-buf and sync

Daniel Stone daniel at fooishbar.org
Mon Aug 24 10:12:49 PDT 2015


On 24 August 2015 at 18:10, Thomas Hellstrom <thellstrom at vmware.com> wrote:
> On 08/24/2015 07:04 PM, Daniel Stone wrote:
>> On 24 August 2015 at 17:56, Thomas Hellstrom <thellstrom at vmware.com> wrote:
>>> On 08/24/2015 05:52 PM, Daniel Stone wrote:
>>>> I still don't think this ameliorates the need for batching: consider
>>>> the case where you update two disjoint screen regions and want them
>>>> both flushed. Either you issue two separate sync calls (which can be
>>>> disadvantageous performance-wise on some hardware / setups), or you
>>>> accumulate the regions and only flush later. So either two ioctls (one
>>>> in the style of dirtyfb and one to perform the sync/flush; you can
>>>> shortcut to assume the full buffer was damaged if the former is
>>>> missing), or one like this:
>>>> struct dma_buf_sync_2d {
>>>>         enum dma_buf_sync_flags flags;
>>>>         __u64 stride_bytes;
>>>>         __u32 bytes_per_pixel;
>>>>         __u32 num_regions;
>>>>         struct {
>>>>                 __u64 x;
>>>>                 __u64 y;
>>>>                 __u64 width;
>>>>                 __u64 height;
>>>>         } regions[];
>>>> };
>>> Fine with me, although perhaps bytes_per_pixel is a bit redundant?
>> Redundant how? It's not implicit in stride.
> For flushing purposes, isn't it possible to cover all cases by assuming
> bytes_per_pixel=1? Not that it matters much.

Sure, though in that case best to replace x with line_byte_offset or
something, because otherwise I guarantee you everyone will get it
wrong, and it'll be a pain to track down. Like how I managed to
misread it now. :)


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