On Fri, May 5, 2017 at 12:52 AM,  [off-list ref] wrote:

? 2017-05-04 21:05?Maxime Ripard ???

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On Thu, May 04, 2017 at 07:48:53PM +0800, Icenowy Zheng wrote:

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Allwinner have a new "Display Engine 2.0" in their new SoCs, which comes
with mixers to do graphic processing and feed data to TCON, like the old
backends and frontends.

Add support for the mixer on Allwinner V3s SoC; it's the simplest one.

Currently a lot of functions are still missing -- more investigations
are needed to gain enough information for them.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
---
Changes in v6:
- Rebased on wens's multi-pipeline patchset.
Changes in v5:
- Changed some code alignment.
- Request real 32-bit DMA (prepare for 64-bit SoCs).
Changes in v4:
- Killed some dead code according to Jernej.

 drivers/gpu/drm/sun4i/Kconfig       |  10 +
 drivers/gpu/drm/sun4i/Makefile      |   3 +
 drivers/gpu/drm/sun4i/sun8i_layer.c | 140 +++++++++++++
 drivers/gpu/drm/sun4i/sun8i_layer.h |  36 ++++
 drivers/gpu/drm/sun4i/sun8i_mixer.c | 394
++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/sun4i/sun8i_mixer.h | 137 +++++++++++++
 6 files changed, 720 insertions(+)
 create mode 100644 drivers/gpu/drm/sun4i/sun8i_layer.c
 create mode 100644 drivers/gpu/drm/sun4i/sun8i_layer.h
 create mode 100644 drivers/gpu/drm/sun4i/sun8i_mixer.c
 create mode 100644 drivers/gpu/drm/sun4i/sun8i_mixer.h

[...]

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diff --git a/drivers/gpu/drm/sun4i/sun8i_mixer.c

b/drivers/gpu/drm/sun4i/sun8i_mixer.c
new file mode 100644
index 000000000000..e216b84d5bb2

--- /dev/null
+++ b/drivers/gpu/drm/sun4i/sun8i_mixer.c

@@ -0,0 +1,394 @@

[...]

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+       list_add_tail(&mixer->engine.list, &drv->engine_list);

You didn't call INIT_LIST_HEAD on that list.

So didn't the sun4i_backend driver...

I think the mixer->engine.list only means an item in the
engine_list, and the drv->engine_list is initialized in the
sun4i_drv source code.

I read [1] that if the item is subsequently added to a list,
you could omit the INIT_LIST_HEAD call.

Makes sense, though you have to be sure you aren't doing anything
else with the list element.

ChenYu

[1] https://isis.poly.edu/kulesh/stuff/src/klist/