linux-kernel - Re: [PATCH v5 05/10] dt-bindings: irqchip: Introduce TISCI Interrupt router bindings

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Message-ID: <6aa37276-0833-fdf5-575b-c3ca14f776a6@ti.com>
Date:   Tue, 19 Feb 2019 21:49:21 +0530
From:   Lokesh Vutla <lokeshvutla@...com>
To:     Tony Lindgren <tony@...mide.com>
CC:     <marc.zyngier@....com>, Nishanth Menon <nm@...com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, <tglx@...utronix.de>,
        <jason@...edaemon.net>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Device Tree Mailing List <devicetree@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>, Tero Kristo <t-kristo@...com>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [PATCH v5 05/10] dt-bindings: irqchip: Introduce TISCI Interrupt
 router bindings



On 2/19/2019 9:05 PM, Tony Lindgren wrote:
> * Lokesh Vutla <lokeshvutla@...com> [190219 08:51]:
>> Hi Tony,
>>
>> On 18/02/19 8:02 PM, Tony Lindgren wrote:
>>> * Lokesh Vutla <lokeshvutla@...com> [190216 03:30]:
>>>> On 2/15/2019 9:46 PM, Tony Lindgren wrote:
>>>>> The dts node for the interrupt controller should describe a
>>>>> proper Linux device, that is with reg entries and so on.
>>>>
>>>> You are asking to just keep the compatible property :)
>>>
>>> Right, and then I realized this node is missing the standard
>>> reg entry too. And you're saying the registers are not even
>>> accissible from Linux.
>>>
>>> So based on that IMO you should not even have a device tree
>>> node for it at all. You should just have the interrupt
>>
>> Practically lets look at what all I am adding in the DT node. Below is one such
>> example:
>>
>> main_intr: interrupt-controller0 {
>> 	compatible = "ti,sci-intr";
>> 	interrupt-controller;
>> 	interrupt-parent = <&gic500>;
>> 	#interrupt-cells = <4>;
>> 	ti,sci = <&dmsc>;
>> 	ti,sci-dst-id = <56>;
>> 	ti,sci-rm-range-girq = <0x1>;
>> };
>>
>> The following 4 properties are required at least for probing, to represent the
>> hierarchy and for  interrupt definition:
>> 	compatible = "ti,sci-intr";
>> 	interrupt-controller;
>> 	interrupt-parent = <&gic500>;
>> 	#interrupt-cells = <4>;
>>
>> The remaining 3 properties represents the TISCI interface. Let's go step by step:
>> * ti,sci = <&dmsc> :This is the phandle to the firmware protocol driver using
>> which the messages are sent
>> * ti,sci-dst-id = <56> : This is the TISCI device ID for the parent controller
>> for which your irqs needs to be connected. As I said this cannot be queried from
>> sysfw and this is the input to the messages that are send to sysfw.
> 
> Let's not add anything that does not describe hardware to the device
> tree. This is ID is an invented number used by the firmware.
> 
>> *  ti,sci-rm-range-girq = <0x1>: This define the ids using which the parent-irq
>> ranges that are allocated to this interrupt router instance can be queried from
>> sysfw.
>> If the above 2 properties are to be added as driver phandle then for every
>> instance of interrupt router in the SoC, a new compatible needs to be created. I
>> don't think this is a desirable solution.
> 
> To me it seems that the interrupt router _must_ have proper IO
> configuration registers available to the Linux running SoC.
> 
> Are you sure the interrupt route does not have proper IO
> configuration registers available for the Linux running SoC?
> 
> If the there are not, I'd be surprised how the SoC is designed :)
> 
> So assuming it does, you should just use the standard device tree
> reg property to differentiate between the various interrupt router
> instances. And then you can have the driver talk to the firmware
> in a way where the driver instances are separate even if no IO
> access to these shared registers is done by the Linux running SoC.
> 
> But see also the mux comment below.
> 
>> With this can you tell me how can we not have a device-tree and still support
>> irq allocation?
> 
> Using standard dts reg property to differentiate the interrupt
> router instances. And if the interrupt router is a mux, you should
> treat it as a mux rather than a chained interrupt controller.
> 
> We do have drivers/mux nowadays, not sure if it helps in this case
> as at least timer interrupts need to be configured very early.
> 
>> Also, this is not the first time a driver based on a firmware is being added.
>> K2g clock, power and reset drivers are based on this where device ids are being
>> passed from consumers. Similarly arm scpi based drivers are also available.
> 
> Having drivers communicate with firmware is quite standard.

yes. How different is this from any of the above mentioned drivers using
firmware specific ids. Like sci pm domain[1] driver utilizes the same
device id for enabling any device in the system. Similarly clock
driver[2] uses the same device ids and clock ids specified by firmware.
There are more which similarly represents firmware ids from DT.

[1] Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
[2] Documentation/devicetree/bindings/clock/ti,sci-clk.txt

Thanks and regards,
Lokesh

> 
> However, stuffing firmware specific data to the device tree
> does not describe the hardware and must not be done.
> 
> Regards,
> 
> Tony
>