Re: [PATCH] drm/mgag200: Hardware cursor support

[Christopher Harvey <charvey@matrox.com>]

On Wed, Jun 05 2013, Christopher Harvey <charvey@matrox.com> wrote:
> G200 cards support, at best, 16 colour palleted images for the cursor
> so we do a conversion in the cursor_set function, and reject cursors
> with more than 16 colours, or cursors with partial transparency. Xorg
> falls back gracefully to software cursors in this case.
>
> We can't disable/enable the cursor hardware without causing momentary
> corruption around the cursor. Instead, once the cursor is on we leave
> it on, and simulate turning the cursor off by moving it
> offscreen. This works well.
>
> Since we can't disable -> update -> enable the cursors, we double
> buffer cursor icons, then just move the base address that points to
> the old cursor, to the new. This also works well, but uses an extra
> page of memory.
>
> The cursor buffers are lazily-allocated on first cursor_set. This is
> to make sure they don't take priority over any framebuffers in case of
> limited memory.
>
> Here is a representation of how the bitmap for the cursor is mapped in G200 memory :
>
>   Each line of color cursor use 6 Slices of 8 bytes. Slices 0 to 3
>   are used for the 4bpp bitmap, slice 4 for XOR mask and slice 5 for
>   AND mask. Each line has the following format:
>
>       //      Byte 0  Byte 1  Byte 2  Byte 3  Byte 4  Byte 5  Byte 6 Byte 7
>       //
>       // S0:  P00-01  P02-03  P04-05  P06-07  P08-09  P10-11  P12-13 P14-15
>       // S1:  P16-17  P18-19  P20-21  P22-23  P24-25  P26-27  P28-29 P30-31
>       // S2:  P32-33  P34-35  P36-37  P38-39  P40-41  P42-43  P44-45 P46-47
>       // S3:  P48-49  P50-51  P52-53  P54-55  P56-57  P58-59  P60-61 P62-63
>       // S4:  X63-56  X55-48  X47-40  X39-32  X31-24  X23-16  X15-08 X07-00
>       // S5:  A63-56  A55-48  A47-40  A39-32  A31-24  A23-16  A15-08 A07-00
>       //
>       //       S0 to S5      = Slices 0 to 5
>       //       P00 to P63    = Bitmap - pixels 0 to 63
>       //       X00 to X63    = always 0 - pixels 0 to 63
>       //       A00 to A63    = transparent markers - pixels 0 to 63
>       //                       1 means colour, 0 means transparent
>
> Signed-off-by: Christopher Harvey <charvey@matrox.com>
> Signed-off-by: Mathieu Larouche <mathieu.larouche@matrox.com>
> Acked-by: Julia Lemire <jlemire@matrox.com>
> Tested-by: Julia Lemire <jlemire@matrox.com>

ping.