Re: [PATCH v4 1/4] dt-bindings: simplefb: Specify node location and handoff related properties

Hi,

On 11/14/2014 10:19 AM, Grant Likely wrote:

On Thu, Nov 13, 2014 at 7:23 PM, Hans de Goede [off-list ref] wrote:

quoted

Since simplefb nodes do not relate directly to hw typically they have been
placed in the root of the devicetree. As the represent runtime information
having them as sub-nodes of /chosen is more logical, specify this.

Also specify when to set the chosen stdout-path property to a simplefb node.

For reliable handover to a hardware specific driver, that driver needs to
know which simplefb to unregister when taking over, specify how the hw driver
can find the matching simplefb node.

Last add some advice on how to fill and use simplefb nodes from a firmware
pov.

Signed-off-by: Hans de Goede <redacted>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Maxime Ripard <redacted>
--
Changes in v2:
-Add stdout-path to the example code
Changes in v3:
-Specify that the node name must be "framebuffer@<address>"
-Specify that the link to link simplefb node and display hw nodes to one
 another for handover goes into the simplefb node, and must be called "display"
-Specify how aliases may be used to tell the OS how to number displays
-Update the example to reflect these changes
Changes in v4:
-Keep the size of the reg property in the example as it was before
---
 .../bindings/video/simple-framebuffer.txt          | 49 +++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/video/simple-framebuffer.txt b/Documentation/devicetree/bindings/video/simple-framebuffer.txt
index 8f35718..c548f33 100644
--- a/Documentation/devicetree/bindings/video/simple-framebuffer.txt
+++ b/Documentation/devicetree/bindings/video/simple-framebuffer.txt

@@ -4,6 +4,31 @@ A simple frame-buffer describes a frame-buffer setup by firmware or
 the bootloader, with the assumption that the display hardware has already
 been set up to scan out from the memory pointed to by the reg property.

+Since simplefb nodes represent runtime information they must be sub-nodes of
+the chosen node (*). Simplefb nodes must be named "framebuffer@<address>".
+
+If a simplefb node represents the preferred console for user interaction,
+then the chosen node's stdout-path property must point to it.

Since we've decided to point the display aliases at the display node
instead of the framebuffer, the stdout-path property should also point
to the display node. The simplefb driver can still work out which
framebuffer to use for stdout path in the same way that it figures out
how to resolve the display alias. This way the stdout details aren't
lost when the framebuffer is disabled and It also means that
stdout-path can be merely set to the alias ("display0") instead of the
full path ("/full/path/to/node").

Ok, will fix for V5.

quoted

+
+If the devicetree contains nodes for the display hardware used by a simplefb,
+then the simplefb node must contain a property called "display", which
+contains a phandle pointing to the primary display hw node, so that the OS
+knows which simplefb to disable when handing over control to a driver for the
+real hardware. The bindings for the hw nodes must specify which node is
+considered the primary node.
+
+It is advised to add display# aliases to help the OS determine how to number
+things. If display# aliases are used, then if the simplefb node contains a

s/then if/and if/

Erm, no the then applies to both the musts following that sentence, in pseudo
code it looks like this:

if (display# aliases are used) {
	if (simplefb node contains a "display" property) {
		/aliases/display# path must point to the display hw node the "display" property points to
	} else {
		/aliases/display# path must point directly to the simplefb node.
	}
}

So no && between the (display# aliases are used) and (simplefb node contains a "display" property)
conditions.

quoted

+"display" property then the /aliases/display# path must point to the display
+hw node the "display" property points to, otherwise it must point directly
+to the simplefb node.
+
+It is advised that devicetree files contain pre-filled, disabled framebuffer
+nodes, so that the firmware only needs to update the mode information and
+enable them. This way if e.g. later on support for more display clocks get
+added, the simplefb nodes will already contain this info and the firmware
+does not need to be updated.

You should merge your guidance of naming pre-filled framebuffer nodes
into this patch. There is no need to have it separate.

Will do for v5.

Regards,

Hans