drm: vkms: Refactor the plane composer to accept new formats

Currently the blend function only accepts XRGB_8888 and ARGB_8888
as a color input.

This patch refactors all the functions related to the plane composition
to overcome this limitation.

The pixels blend is done using the new internal format. And new handlers
are being added to convert a specific format to/from this internal format.

So the blend operation depends on these handlers to convert to this common
format. The blended result, if necessary, is converted to the writeback
buffer format.

This patch introduces three major differences to the blend function.
1 - All the planes are blended at once.
2 - The blend calculus is done as per line instead of per pixel.
3 - It is responsible to calculates the CRC and writing the writeback
buffer(if necessary).

These changes allow us to allocate way less memory in the intermediate
buffer to compute these operations. Because now we don't need to
have the entire intermediate image lines at once, just one line is
enough.

| Memory consumption (output dimensions) |
|:--------------------------------------:|
|       Current      |     This patch    |
|:------------------:|:-----------------:|
|   Width * Heigth   |     2 * Width     |

Beyond memory, we also have a minor performance benefit from all
these changes. Results running the IGT[1] test
`igt@kms_cursor_crc@pipe-a-cursor-512x512-onscreen` ten times:

|                 Frametime                  |
|:------------------------------------------:|
|  Implementation |  Current  |  This commit |
|:---------------:|:---------:|:------------:|
| frametime range |  9~22 ms  |    5~17 ms   |
|     Average     |  11.4 ms  |    7.8 ms    |

[1] IGT commit id: bc3f6833a12221a46659535dac06ebb312490eb4

V2: Improves the performance drastically, by performing the operations
    per-line and not per-pixel(Pekka Paalanen).
    Minor improvements(Pekka Paalanen).
V3: Changes the code to blend the planes all at once. This improves
    performance, memory consumption, and removes much of the weirdness
    of the V2(Pekka Paalanen and me).
    Minor improvements(Pekka Paalanen and me).
V4: Rebase the code and adapt it to the new NUM_OVERLAY_PLANES constant.
V5: Minor checkpatch fixes and the removal of TO-DO item(Melissa Wen).
    Several security/robustness improvents(Pekka Paalanen).
    Removes check_planes_x_bounds function and allows partial
    partly off-screen(Pekka Paalanen).
V6: Fix a mismatch of some variable sizes (Pekka Paalanen).
    Several minor improvements (Pekka Paalanen).

Reviewed-by: Melissa Wen <mwen@igalia.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Igor Torrente <igormtorrente@gmail.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220905190811.25024-7-igormtorrente@gmail.com

1 files changed, 0 insertions, 4 deletions

diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index 973e2d43108b..a49e4ae92653 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -118,10 +118,6 @@ Add Plane Features
 
 There's lots of plane features we could add support for:
 
-- Clearing primary plane: clear primary plane before plane composition (at the
-  start) for correctness of pixel blend ops. It also guarantees alpha channel
-  is cleared in the target buffer for stable crc. [Good to get started]
-
 - ARGB format on primary plane: blend the primary plane into background with
   translucent alpha.