Chris,

This looks like a hw specific value which is difficult to understand. However, the definition of these values are just a list of available options of z-order. On Intel VLV, there is only 6 options for the three planes Primary, Sprite A and Sprite B. Cursor is always on top. For example, "P1S1S2C1" means z-order (from bottom to top) of Primary -> Sprite A -> Sprite B -> Cursor.

#define P1S1S2C1        0
#define P1S2S1C1        8
#define S2P1S1C1        1
#define S2S1P1C1        9
#define S1P1S2C1        4
#define S1S2P1C1        6

In theory, if hw supports, each CRTC may have their own plane z-order if user intentionally wants that happens. The pipe info (0 or 1) is packed into z-order value with extra bit (bit 31).

Thanks,
Alex

On 14-03-04 12:20 AM, Chris Wilson wrote:
> On Mon, Mar 03, 2014 at 02:12:28PM -0800, yu.dai@intel.com wrote:
>> From: "Yu(Alex) Dai" <yu.dai@intel.com>
>>
>> Add "zorder" property to crtc to control Z-order of sprite and
>> primary planes. The alpha channel of the planes can be enabled or
>> disabled during Z-order change.
>
> Can I just say that is an abonimal user interface. You expect the
> client to encode a hw specific value into a CRTC property that
> affects global state. and given the two properties on the two CRTCs,
> which should userspace believe? -Chris
>