On Mon, Jan 21, 2019 at 11:53 AM Russell King - ARM Linux admin linux@armlinux.org.uk wrote:
On Mon, Jan 21, 2019 at 10:07:11AM -0600, Rob Herring wrote:
On Mon, Jan 21, 2019 at 9:46 AM Lubomir Rintel lkundrak@v3.sk wrote:
On Mon, 2019-01-21 at 09:35 -0600, Rob Herring wrote:
On Sun, Jan 20, 2019 at 11:26 AM Lubomir Rintel lkundrak@v3.sk wrote:
The Marvell Armada DRM master device is a virtual device needed to list all nodes that comprise the graphics subsystem.
Signed-off-by: Lubomir Rintel lkundrak@v3.sk
.../display/armada/marvell-armada-drm.txt | 24 +++++++++++++++++++ 1 file changed, 24 insertions(+)
diff --git a/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt b/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt index de4cca9432c8..3dbfa8047f0b 100644 --- a/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt +++ b/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt @@ -1,3 +1,27 @@ +Marvell Armada DRM master device +================================
+The Marvell Armada DRM master device is a virtual device needed to list all +nodes that comprise the graphics subsystem.
+Required properties:
- compatible: value should be "marvell,dove-display-subsystem",
- "marvell,armada-display-subsystem"
- ports: a list of phandles pointing to display interface ports of CRTC
- devices
- memory-region: phandle to a node describing memory to be used for the
- framebuffer
+Example:
display-subsystem {compatible = "marvell,dove-display-subsystem","marvell,armada-display-subsystem";memory-region = <&display_reserved>;ports = <&lcd0_port>;If there is only one device, you don't need this virtual node.
By "one device" you mean one LCD controller (CRTC)?
Yes.
How does that work (as far as the Linux implementation) ? I can't see a way that could work, while allowing the flexibility that Armada DRM allows (two completely independent LCD controllers as two separate DRM devices vs one DRM device containing both LCD controllers.)
I suppose in the (single CRTC) example case, the display-subsystem node used to associate it with the memory region reserved for allocating the frame buffers from. Could that be done differently?
Move memory-region to the LCD controller node.
That doesn't work - it would appear in the wrong part of the driver.
Why? You can fetch properties from other nodes.
If you have 2 CRTCs, do you have 1 or 2 reserved memory regions? I'd think 2 with each one in the corresponding LCDC that uses them would be more flexible.
Or just get the data out of the /reserved-memory node directly. Surely it has a compatible that you can find it with.
Also, if the node is indeed made optional, then it's going to complicate things on the DRM side. Currently the driver that binds to the node creates the DRM device once it sees all the components connected to the ports appear. If we loose it, then the LCD controller driver would somehow need to find out that it's alone and create the DRM device itself.
DT is not the only way to create devices. The DRM driver can bind to the LCDC node and then create a child CRTC device (or even multiple ones for h/w with multiple pipelines).
That seems completely upside down and rediculous to me - are you really suggesting that we should have some kind of virtual device in DT, and omit the _real_ physical devices for that, having the driver create the device with all the appropriate SoC resources?
We create child platform devices that inherit from the parent in DT all the time. MFD child drivers are a common case. Sometime the child devices have DT nodes and sometimes they don't.
Otherwise, do it the other way around. Create a virtual DRM device conditioned on the SoC:
if (of_machine_is_compatible("foo,bar")) platform_device_register_simple(...)
You'll also notice that there are only 3 cases of this virtual node in the tree: STi, i.MX IPU, and Rockchip. That's because we've deprecated doing these virtual nodes for some time now. IOW, there are several examples of how to do this without a virtual node.
This driver has been in-tree with this setup for some time, although the documentation has been missing (we actually have a _lot_ of instances of that.) However, we have no in-tree DT using it.
The current Armada DRM driver has no binding to DT at all, so no, it is not just missing documentation or a dts file.
I don't really see how to satisfy your comments without totally restructuring the driver, which is going to be quite a big chunk of work. I'm not sure I have the motivation to do that right now.
It's not a big chunk of work. Look at commit 246774d17fc0 ("drm/etnaviv: remove the need for a gpu-subsystem DT node") for an example.
Rob