[PATCH] ARM: dts: sun4i: Add simplefb node with de_fe0-de_be0-lcd0-hdmi pipeline

On Mon, Jan 19, 2015 at 02:35:41PM +0100, Hans de Goede wrote:

Hi,

On 19-01-15 14:20, Maxime Ripard wrote:

quoted

Hi Hans,

On Mon, Jan 19, 2015 at 02:01:17PM +0100, Hans de Goede wrote:

quoted

Testing has shown that on sun4i the display backend engine does not have
deep enough fifo-s causing flickering / tearing in full-hd mode due to
fifo underruns. This can be avoided by letting the display frontend engine
do the dma from memory, and then letting it feed the data directly into
the backend unmodified, as the frontend does have deep enough fifo-s.

Note since u-boot-v2015.01 has been released using the de_be0-lcd0-hdmi
pipeline on sun4i, we need to keep that one around too (unfortunately).

Signed-off-by: Hans de Goede <redacted>
---
 arch/arm/boot/dts/sun4i-a10.dtsi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/boot/dts/sun4i-a10.dtsi b/arch/arm/boot/dts/sun4i-a10.dtsi
index f5e35b5..ccd60e3 100644
--- a/arch/arm/boot/dts/sun4i-a10.dtsi
+++ b/arch/arm/boot/dts/sun4i-a10.dtsi

@@ -44,6 +44,14 @@
 				 <&ahb_gates 44>;
 			status = "disabled";
 		};
+
+		framebuffer at 1 {
+			compatible = "allwinner,simple-framebuffer", "simple-framebuffer";
+			allwinner,pipeline = "de_fe0-de_be0-lcd0-hdmi";
+			clocks = <&pll5 1>, <&ahb_gates 36>, <&ahb_gates 43>,
+				 <&ahb_gates 44>, <&ahb_gates 46>;
+			status = "disabled";
+		};

Thanks for this.

I do have a question though, maybe I'm missing something, but what
would prevent us from using the existing node already? The output
pipeline seems to be the same, at least for which output we
use. Wether we use or not the display frontend looks like an
implementation detail.

The purpose of having a node per pipeline is to have the rights clocks
listed for the pipeline chosen. So the "de_fe0-de_be0-lcd0-hdmi" node
has one ahb_gates entry more so as to make sure the kernel does not gate
off the frontend.

The idea of having different nodes per pipeline is that when we get
support for more module clocks in place, as a preparation for kms
support, we can add the module clocks to the relevant nodes, to also
ensure the module clocks will not get turned off.

By having this info in the dtb, rather then in u-boot we can update
the clocks list as we add new clock nodes in the dtb, ensuring that
an older u-boot will keep working as we add support for module
clocks, etc.

Yeah, I know that, and it's exactly why we have these nodes
pre-populated it. But my point was exactly that: Why not leverage the
fact that we have that possibility to add the missing clock for the
frontend, and just use that.

quoted

That or just having several strings in allwinner,pipeline.

If this simplefb binding is just going to be a collection of all the
various combinations we have, plus the legacy options, I'm a bit
worried that this is just going to be a hell to maintain, without any
way to remove it at compile time (if such feature is ever merged in
DTC).

I can understand where you're coming from, I wish I could say there
will be no more surprises / additions, but I don't want to make
promises I cannot keep. I do not see u-boot adding support for multiple
displays anytime soon, so things should stay limited to 3 nodes (one for
hdmi, lcd and vga each) or 2 nodes on socs without hdmi.

Except on sun4i where we need 2 for hdmi for compat reasons for a total
of 4.

But my crystal ball is defunct, so I cannot promise things will stay
limited to this.

Heh :)

I'm not really asking for a crystal ball. I even expect that list to
grow, as some board will probably need the second display engine on
SoCs that have one, and that's ok. But my concern is more that we will
end up with multiple similar options, including ones that we know are
not in use, but can't really remove either.

But yeah, ok.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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