On 4/18/2018 2:57 PM, Jae Hyun Yoo wrote:

On 4/18/2018 2:28 PM, Rob Herring wrote:

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On Wed, Apr 18, 2018 at 3:28 PM, Jae Hyun Yoo
[off-list ref] wrote:

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On 4/18/2018 7:32 AM, Rob Herring wrote:

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On Tue, Apr 17, 2018 at 3:40 PM, Jae Hyun Yoo
[off-list ref] wrote:

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On 4/16/2018 4:51 PM, Jae Hyun Yoo wrote:

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On 4/16/2018 4:22 PM, Jae Hyun Yoo wrote:

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On 4/16/2018 11:14 AM, Rob Herring wrote:

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On Tue, Apr 10, 2018 at 11:32:09AM -0700, Jae Hyun Yoo wrote:

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This commit adds dt-bindings documents for PECI cputemp and 
dimmtemp
client
drivers.

[...]

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+Example:
+??? peci-bus at 0 {
+??????? #address-cells = <1>;
+??????? #size-cells = <0>;
+??????? < more properties >
+
+??????? peci-dimmtemp at cpu0 {

unit-address is wrong.

Will fix it using the reg value.

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It is a different bus from cputemp? Otherwise, you have conflicting
addresses. If that's the case, probably should make it clear by
showing
different host adapters for each example.

It could be the same bus with cputemp. Also, client address 
sharing is
possible by PECI core if the functionality is different. I mean,
cputemp and
dimmtemp targeting the same client is possible case like this.
peci-cputemp at 30
peci-dimmtemp at 30

Oh, I got your point. Probably, I should change these separate 
settings
into one like

peci-client at 30 {
?????? compatible = "intel,peci-client";
?????? reg = <0x30>;
};

Then cputemp and dimmtemp drivers could refer the same compatible
string.
Will rewrite it.

I've checked it again and realized that it should use function 
based node
name like:

peci-cputemp at 30
peci-dimmtemp at 30

If it use the same string like 'peci-client at 30', the drivers cannot be
selectively enabled. The client address sharing way is well handled in
PECI
core and this way would be better for the future implementations of 
other
PECI functional drivers such as crash dump driver and so on. So I'm 
going
change the unit-address only.

2 nodes at the same address is wrong (and soon dtc will warn you on
this). You have 2 potential options. The first is you need additional
address information in the DT if these are in fact 2 independent
devices. This could be something like a function number to use
something from PCI addressing. From what I found on PECI, it doesn't
seem to have anything like that. The 2nd option is you have a single
DT node which registers multiple hwmon devices. DT nodes and drivers
don't have to be 1-1. Don't design your DT nodes from how you want to
partition drivers in some OS.

Rob

Please correct me if I'm wrong but I'm still thinking that it is
possible. Also, I did compile it but dtc doesn't make a warning. Let me
show an another use case which is similar to this case:

I did say *soon*. It's in dtc repo, but not the kernel copy yet.

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In arch/arm/boot/dts/aspeed-g5.dtsi
[...]
lpc_host: lpc-host at 80 {
???????? compatible = "aspeed,ast2500-lpc-host", "simple-mfd", "syscon";
???????? reg = <0x80 0x1e0>;
???????? reg-io-width = <4>;

???????? #address-cells = <1>;
???????? #size-cells = <1>;
???????? ranges = <0x0 0x80 0x1e0>;

???????? lpc_ctrl: lpc-ctrl at 0 {
???????????????? compatible = "aspeed,ast2500-lpc-ctrl";
???????????????? reg = <0x0 0x80>;
???????????????? clocks = <&syscon ASPEED_CLK_GATE_LCLK>;
???????????????? status = "disabled";
???????? };

???????? lpc_snoop: lpc-snoop at 0 {
???????????????? compatible = "aspeed,ast2500-lpc-snoop";
???????????????? reg = <0x0 0x80>;
???????????????? interrupts = <8>;
???????????????? status = "disabled";
???????? };
}
[...]

This is device tree setting for LPC interface and its child nodes.
LPC interface can be used as a multi-functional interface such as
snoop 80, KCS, SIO and so on. In this use case, lpc-ctrl at 0 and
lpc-snoop at 0 are sharing their address range from their individual
driver modules and they can be registered quite well through both
static dt or dynamic dtoverlay. PECI is also a multi-functional
interface which is similar to the above case, I think.

This case too is poor design and should be fixed as well. Simply put,
you can have 2 devices on a bus at the same address without some sort
of mux or arbitration device in the middle. If you have a device/block
with multiple functions provided to the OS, then it is the OS's
problem to arbitrate access. It is not a DT problem because OS's can
vary in how they handle that both from OS to OS and over time.

Rob

If I change it to a single DT node which registers 2 hwmon devices using
the 2nd option above, then I still have 2 devices on a bus at the same
address. Does it also make a problem to the OS then?

Jae

Additionally, I need to explain that there is one and only bus host
(adapter) and multiple clients on a PECI bus, and PECI spec doesn't
allow multiple originators so only the host device can originate
message. In this implementation, all message transactions on a bus from
client driver modules and user space will be serialized well in the PECI
core bus driver so bus occupation and traffic arbitration will be
managed well in the PECI core bus driver even in case of a bus has 2 
client drivers at the same address. I'm sure that this implementation 
doesn't make that kind of problem to OS.

Jae