On 06/28/2016 03:15 AM, Joseph Lo wrote:

On 06/27/2016 11:55 PM, Stephen Warren wrote:

quoted

On 06/27/2016 03:02 AM, Joseph Lo wrote:

quoted

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.

quoted

quoted

diff --git
a/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt
b/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt

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+- 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:

- 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.

That should be OK; adding more entries in interrupt-names is backwards 
compatible. Still, since the HW is fixed, it would be nice to just get 
the complete list documented up front if possible.

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+- 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?

Yes, that would be (b) above.

However, please do note (a): I expect that splitting things up will turn 
out to be a mistake, as it has for other HW modules in the past. I would 
far rather see a single hsp node in DT, since there is a single HSP 
block in HW. Sure that block has multiple sub-functions. However, there 
is common logic that affects all of those sub-functions and binds 
everything into a single HW module. If you represent the HW module using 
multiple different DT nodes, it will be hard to correctly represent that 
common logic. Conversely, I see no real advantage to splitting up the DT 
node. I strongly believe we should have a single "hsp" node in DT.

Internally, the SW driver for that node can be structured however you 
want; it could register with multiple subsystems (mailbox, ...) with 
just one struct device, or the HSP driver could be an MFD device with 
sub-drivers for each separate piece of functionality the HW implements. 
All this can easily be done even while using a single DT node. And 
furthermore, we can add this SW structure later if/when we actually need 
it; in other words, there's no need to change your current patches right 
now, except to remove the nvidia,hsp-function DT property.
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