Re: [PATCH 01/10] Documentation: dt-bindings: mailbox: tegra: Add binding for HSP mailbox
From: Joseph Lo
Date: Tue Jun 28 2016 - 05:15:48 EST
On 06/27/2016 11:55 PM, Stephen Warren wrote:
On 06/27/2016 03:02 AM, Joseph Lo wrote:
Add DT binding for the Hardware Synchronization Primitives (HSP). The
HSP is designed for the processors to share resources and communicate
together. It provides a set of hardware synchronization primitives for
interprocessor communication. So the interprocessor communication (IPC)
protocols can use hardware synchronization primitive, when operating
between two processors not in an SMP relationship.
This binding is quite different to the binding you sent to internal IP
review. I wonder why it changed? Specific comments below:
Due to some enhancements for supporting multiple functions of HSP
sub-modules in the same driver, I re-wrote some parts of the bindings
and driver.
diff --git
a/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt
b/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt
+NVIDIA Tegra Hardware Synchronization Primitives (HSP)
+
+The HSP modules are used for the processors to share resources and
communicate
+together. It provides a set of hardware synchronization primitives for
+interprocessor communication. So the interprocessor communication (IPC)
+protocols can use hardware synchronization primitives, when operating
between
+two processors not in an SMP relationship.
+
+The features that HSP supported are shared mailboxes, shared semaphores,
+arbitrated semaphores and doorbells.
+
+Required properties:
+- name : Should be hsp
+- compatible : Should be "nvidia,tegra<chip>-hsp"
I think this should explicitly list the value values of the compatible
property, rather than being a generic/wildcard description:
- compatible
Array of strings.
One of:
- "nvidia,tegra186-hsp"
If/when this binding supports other SoCs in the future, we'll add more
entries into that list.
+- reg : Offset and length of the register set for the device
+- interrupts : Should contain the HSP interrupts
+- interrupt-names: Should contain the names of the HSP interrupts
that the
+ client are using.
+ "doorbell"
The binding should describe the HW, and not be affected by anything
"that the client(s) are using". If there are multiple interrupts, we
should list them all here, from the start.
When revising this, I would consider the following wording canonical:
Okay.
- interrupt-names
Array of strings.
Contains a list of names for the interrupts described by the
interrupts property. May contain the following entries, in any
order:
- "doorbell"
- "..." (no doubt many more items will be listed here, e.g.
for semaphores, etc.).
I think I will just list "doorbell" for now. And adding more later once
we add other HSP sub-module support.
Users of this binding MUST look up entries in the interrupts
property by name, using this interrupts-names property to do so.
- interrupts
Array of interrupt specifiers.
Must contain one entry per entry in the interrupt-names property,
in a matching order.
+- nvidia,hsp-function : Specifies one of the HSP functions that the
HSP unit
+ will be supported. The function ID can be found in the
+ header file <dt-bindings/mailbox/tegra-hsp.h>.
This property wasn't in the internal patch.
This doesn't make sense. The HW feature-set is fixed. This sounds like
some kind of software configuration option, or a way to allow different
drivers to handle different aspects of the HW? In general, the binding
shouldn't be influenced by software structure. Please delete this property.
Now, if you're attempting to set up a binding where each function
(semaphores, shared mailboxes, doorbells, etc.) has a different DT node,
then (a) splitting up HW modules into sub-blocks has usually turned out
to be a mistake in the past, and (b) the differences should likely be
represented by using a different compatible property for each
sub-component, rather than via a custom property.
Currently the usage of HSP HW in the downstream kernel is something like
the model below.
remote_processor_A-\
remote_processor_B--->hsp@1000 (doorbell func) <-> host CPU
remote_processor_C-/
remote_processor_D -> hsp@2000 (shared mailbox) <-> CPU
remote_processor_E -> hsp@3000 (shared mailbox) <-> CPU
I am thinking if we can just add the appropriate compatible strings for
it to replace "nvidia,tegra186-hsp". e.g. "nvidia,tegra186-hsp-doorbell"
and "nvidia,tegra186-hsp-sharedmailbox". So the driver can probe and
initialize correctly depend on the compatible property. How do you think
about it? Is this the same as the (b) you mentioned above?
The following properties were included in the internal patch:
nvidia,num-SM = <0x8>;
nvidia,num-AS = <0x2>;
nvidia,num-SS = <0x2>;
nvidia,num-DB = <0x7>;
nvidia,num-SI = <0x8>;
... yet aren't here. True the compatible value implies those values; was
that why the properties were removed?
Because these values are available in the HSP_INT_DIMENSIONING register,
so remove them.
+Example:
+
+hsp_top: hsp@3c00000 {
...
+bpmp@d0000000 {
+ ...
+ mboxes = <&hsp_top HSP_DB_MASTER_BPMP>;
+ ...
+};
I'd suggest not including the bpmp node in the example, since it's not
part of the HSP node. If you do, recall that bpmp has no reg property
and hence the node name shouldn't include a unit address.
Okay.
diff --git a/include/dt-bindings/mailbox/tegra-hsp.h
b/include/dt-bindings/mailbox/tegra-hsp.h
This file should probably be named tegra186-hsp, since I doubt the
master ID values will be stable between chips.
Yes, true. Will fix.
+/*
+ * This header provides constants for binding nvidia,tegra<chip>-hsp.
That should say "186" not "<chip>"
+#ifndef _DT_BINDINGS_MAILBOX_TEGRA186_HSP_H
+#define _DT_BINDINGS_MAILBOX_TEGRA186_HSP_H
The two changes mentioned above would be consistent with that include
guard's name including the text "186".
+#define HSP_SHARED_MAILBOX 0
+#define HSP_SHARED_SEMAPHORE 1
+#define HSP_ARBITRATED_SEMAPHORE 2
+#define HSP_DOORBELL 3
I think those should be removed, along with the nvidia,hsp-function
property.
Okay.
Thanks,
-Joseph