Re: [PATCH v7 01/12] dt-bindings: add img,pvrsgx.yaml for Imagination GPUs
From: Paul Cercueil
Date: Sun May 03 2020 - 08:52:25 EST
Hi Nikolaus,
Le sam. 2 mai 2020 à 22:26, H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> a
écrit :
Hi Paul,
Am 26.04.2020 um 15:11 schrieb Paul Cercueil <paul@xxxxxxxxxxxxxxx>:
Hi Nikolaus,
Le ven. 24 avril 2020 à 22:34, H. Nikolaus Schaller
<hns@xxxxxxxxxxxxx> a écrit :
The Imagination PVR/SGX GPU is part of several SoC from
multiple vendors, e.g. TI OMAP, Ingenic JZ4780, Intel Poulsbo,
Allwinner A83 and others.
With this binding, we describe how the SGX processor is
interfaced to the SoC (registers and interrupt).
The interface also consists of clocks, reset, power but
information from data sheets is vague and some SoC integrators
(TI) deciced to use a PRCM wrapper (ti,sysc) which does
all clock, reset and power-management through registers
outside of the sgx register block.
Therefore all these properties are optional.
Tested by make dt_binding_check
Signed-off-by: H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>
---
.../devicetree/bindings/gpu/img,pvrsgx.yaml | 150
++++++++++++++++++
1 file changed, 150 insertions(+)
create mode 100644
Documentation/devicetree/bindings/gpu/img,pvrsgx.yaml
diff --git a/Documentation/devicetree/bindings/gpu/img,pvrsgx.yaml
b/Documentation/devicetree/bindings/gpu/img,pvrsgx.yaml
new file mode 100644
index 000000000000..33a9c4c6e784
--- /dev/null
+++ b/Documentation/devicetree/bindings/gpu/img,pvrsgx.yaml
@@ -0,0 +1,150 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpu/img,pvrsgx.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Imagination PVR/SGX GPU
+
+maintainers:
+ - H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>
+
+description: |+
+ This binding describes the Imagination SGX5 series of 3D
accelerators which
+ are found in several different SoC like TI OMAP, Sitara,
Ingenic JZ4780,
+ Allwinner A83, and Intel Poulsbo and CedarView and more.
+
+ For an extensive list see:
https://en.wikipedia.org/wiki/PowerVR#Implementations
+
+ The SGX node is usually a child node of some DT node belonging
to the SoC
+ which handles clocks, reset and general address space mapping
of the SGX
+ register area. If not, an optional clock can be specified here.
+
+properties:
+ $nodename:
+ pattern: '^gpu@[a-f0-9]+$'
+ compatible:
+ oneOf:
+ - description: SGX530-121 based SoC
+ items:
+ - enum:
+ - ti,omap3-sgx530-121 # BeagleBoard A/B/C,
OpenPandora 600MHz and similar
+ - const: img,sgx530-121
+ - const: img,sgx530
+
+ - description: SGX530-125 based SoC
+ items:
+ - enum:
+ - ti,am3352-sgx530-125 # BeagleBone Black
+ - ti,am3517-sgx530-125
+ - ti,am4-sgx530-125
+ - ti,omap3-sgx530-125 # BeagleBoard XM, GTA04,
OpenPandora 1GHz and similar
+ - ti,ti81xx-sgx530-125
+ - const: ti,omap3-sgx530-125
+ - const: img,sgx530-125
+ - const: img,sgx530
+
+ - description: SGX535-116 based SoC
+ items:
+ - const: intel,poulsbo-gma500-sgx535 # Atom Z5xx
+ - const: img,sgx535-116
+ - const: img,sgx535
+
+ - description: SGX540-116 based SoC
+ items:
+ - const: intel,medfield-gma-sgx540 # Atom Z24xx
+ - const: img,sgx540-116
+ - const: img,sgx540
+
+ - description: SGX540-120 based SoC
+ items:
+ - enum:
+ - samsung,s5pv210-sgx540-120
+ - ti,omap4-sgx540-120 # Pandaboard, Pandaboard ES and
similar
+ - const: img,sgx540-120
+ - const: img,sgx540
+
+ - description: SGX540-130 based SoC
+ items:
+ - enum:
+ - ingenic,jz4780-sgx540-130 # CI20
+ - const: img,sgx540-130
+ - const: img,sgx540
+
+ - description: SGX544-112 based SoC
+ items:
+ - const: ti,omap4470-sgx544-112
+ - const: img,sgx544-112
+ - const: img,sgx544
+
+ - description: SGX544-115 based SoC
+ items:
+ - enum:
+ - allwinner,sun8i-a31-sgx544-115
+ - allwinner,sun8i-a31s-sgx544-115
+ - allwinner,sun8i-a83t-sgx544-115 # Banana-Pi-M3
(Allwinner A83T) and similar
+ - const: img,sgx544-115
+ - const: img,sgx544
+
+ - description: SGX544-116 based SoC
+ items:
+ - enum:
+ - ti,dra7-sgx544-116 # DRA7
+ - ti,omap5-sgx544-116 # OMAP5 UEVM, Pyra Handheld and
similar
+ - const: img,sgx544-116
+ - const: img,sgx544
+
+ - description: SGX545 based SoC
+ items:
+ - const: intel,cedarview-gma3600-sgx545 # Atom N2600,
D2500
+ - const: img,sgx545-116
+ - const: img,sgx545
+
+ reg:
+ maxItems: 1
+
+ interrupts:
+ maxItems: 1
+
+ interrupt-names:
+ maxItems: 1
+ items:
+ - const: sgx
+
+ clocks:
+ maxItems: 4
+
+ clock-names:
+ maxItems: 4
+ items:
+ - const: core
+ - const: sys
+ - const: mem
+ - const: hyd
+
+ sgx-supply: true
+
+ power-domains:
+ maxItems: 1
+
+ resets:
+ maxItems: 1
+
+required:
+ - compatible
+ - reg
+ - interrupts
By not making 'clocks' required you make it possible to create
broken bindings; according to your schema, a GPU node without a
'clocks' for the JZ4780 would be perfectly valid.
Yes. But it will never pass a test with real hardware. So it can't be
omitted anyways.
On a more general thought, this argument holds for any optional
property. So it is not specific to clocks. Since the reg address
values are also never specified you can still create broken bindings.
Or by connecting the wrong clock. So the ways to create broken
bindings are numerous.
I also assume that SGX integrators are not beginners and do you think
they need to find out through a make dt_binding_check dtbs_check that
they should define a clock? based on *assumptions* we do without
having access to all systems?
IMHO the bindings documentation is a documentation. So it needs to be
helpful but not perfect. Formalizing all corner cases in a bindings
document (just because we can since .yaml was introduced) is IMHO
overkill.
In times before the introduction of more formal .yaml I think we
would not even have considered this for a comment in the bindings.txt.
It's possible to forbid the presence of the 'clocks' property on
some implementations, and require it on others.
To be precise we have to specify the exact number of clocks (between
0 and 4) for every architecture.
This also contradicts my dream to get rid of the architecture
specific components in the long run. My dream (because I can't tell
how it can be done) is that we can one day develop something which
just needs compatible = img,530 or imp,540 or img,544. Then we can't
make the number clocks depend on the implementation any more.
As we said before, the number of clocks is a property of the GPU and
*not* its integration into the SoC.
So you would *not* have a number of clocks between 0 and 4. You get
either 0, or 4, depending on whether or not you have a wrapper.
See how it's done for instance on
Documentation/devicetree/bindings/serial/samsung_uart.yaml.
Yes I know the design pattern, but I wonder if such a move makes the
whole thing even less maintainable.
Assume we have finished DTS for some SoC. Then these DTS have been
tested on real hardware and are working. Clocks are there where
needed and missing where not. We may now forbid or not forbid them
for some implementations in the bindings.yaml but the result of
dtbs_check won't change! Because they are tested and working and the
bindings.yaml has been adapted to the result. So we have just
duplicated something for no practical benefit.
Next, assume there is coming support for more and more new SoC. Then,
developers not only have to figure out which clocks they need in the
DTS but they also have to add a patch to the implementation specific
part of the bindings.yaml to clearly define exactly the same what
they already have written into their .dts (the clocks are either
there for the of_node or they are not). So again the rules are for no
benefit, since a new SoC is introduced exactly once. And tested if it
works. And if it is there, it will stay as it is. It is just work for
maintainers to review that patch as well.
If you add support for a new SoC, you'd still need to modify the
binding to add the compatible string. So the argument of "more work" is
moot.
-Paul
It boils down to the question if we need to formalize the rule how a
working DTS was derived. Or just have a working DTS and not formalize
everything.
So IMHO carrying along such a detail (forbid clocks on some
architectures) is nice to have (and fun to learn the .yaml thing) but
not of benefit for anyone. Not for the DTS developer nor for the
maintainers nor for the users of a Linux kernel. "Keep it simple" is
always a good rule for maintainability.
In summary I don't see a good reason to follow this in v8. But you
could add it by a separate patch later if the DTS have been reviewed
and agreed.
BR and thanks,
Nikolaus