Date:   Thu, 29 Nov 2018 10:49:21 +0200
From:   Roger Quadros <rogerq@...com>
To:     David Lechner <david@...hnology.com>, <tony@...mide.com>
CC:     <robh+dt@...nel.org>, <bcousson@...libre.com>,
        <ssantosh@...nel.org>, <ohad@...ery.com>,
        <bjorn.andersson@...aro.org>, <s-anna@...com>, <nsekhar@...com>,
        <t-kristo@...com>, <nsaulnier@...com>, <jreeder@...com>,
        <m-karicheri2@...com>, <woods.technical@...il.com>,
        <linux-omap@...r.kernel.org>, <linux-remoteproc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH 01/17] dt-bindings: remoteproc: Add TI PRUSS bindings

David,

On 28/11/18 17:42, David Lechner wrote:
> On 11/27/18 9:15 AM, Roger Quadros wrote:
>>
>> On 26/11/18 23:14, David Lechner wrote:
>>> On 11/22/18 5:38 AM, Roger Quadros wrote:
>>>> From: Suman Anna <s-anna@...com>
>>>>
>>>> This patch adds the bindings for the Programmable Real-Time Unit
>>>> and Industrial Communication Subsystem (PRU-ICSS) present on various
>>>> TI SoCs. The IP is present on multiple TI SoC architecture families
>>>> including the OMAP architecture SoCs such as AM33xx, AM437x and
>>>> AM57xx; and on a Keystone 2 architecture based 66AK2G SoC. It is
>>>> also present on the Davinci based OMAPL138 SoCs and K3 architecture
>>>> based AM65x SoCs as well (not covered for now). Details have been
>>>> added to include bindings for various core sub-modules like the PRU
>>>> Cores, the PRUSS Interrupt Controller, and other sub-modules used
>>>> for Industrial Communication purposes, covering the MDIO, MII_RT
>>>> and the IEP sub-modules. The binding mostly uses standard DT
>>>> properties.
>>>>
>>>> Signed-off-by: Suman Anna <s-anna@...com>
>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>> ---
>>>>    .../devicetree/bindings/soc/ti/ti,pruss.txt        | 360 +++++++++++++++++++++
>>>>    1 file changed, 360 insertions(+)
>>>>    create mode 100644 Documentation/devicetree/bindings/soc/ti/ti,pruss.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/soc/ti/ti,pruss.txt b/Documentation/devicetree/bindings/soc/ti/ti,pruss.txt
>>>> new file mode 100644
>>>> index 0000000..24fedad
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/soc/ti/ti,pruss.txt
>>>
>>> ...
>>>
>>>> +
>>>> +PRU-ICSS SoC Bus Parent Node
>>>> +=============================
>>>> +This node represents the integration of the PRU-ICSS IP into a SoC, and is
>>>> +required for all SoCs. The PRU-ICSS parent nodes need to be defined as child
>>>> +nodes of this node.
>>>> +
>>>> +Required Properties:
>>>> +--------------------
>>>> +- compatible     : should be one of,
>>>> +                       "ti,am3356-pruss-soc-bus" for AM335x family of SoCs
>>>> +                       "ti,am4376-pruss-soc-bus" for AM437x family of SoCs
>>>> +                       "ti,am5728-pruss-soc-bus" for AM57xx family of SoCs
>>>> +                       "ti,k2g-pruss-soc-bus" for 66AK2G family of SoCs
>>>> +- reg            : address and size of the PRUSS CFG sub-module registers
>>>> +                   dictating the interconnect configuration
>>>
>>> I haven't looked into Tony's suggestion of using ti-sysc yet, so this may be a
>>> moot point, but how will this work with AM18xx that does not have a PRUSS CFG
>>> register? It seems to me that reg here should be the address and size of the
>>> entire PRUSS IP block and the CFG register should be a syscon node or something
>>> like that.
>>
>> The reg property description is incorrect in the patch. It should have been
>>
>> reg        : address of SYSCFG register.
>>
>> The SYSCFG register is used to enable and reset the module.
>>
>> But based on Tony's suggestion this wrapper driver will change to ti,sysc for
>> OMAP like SoCs.
>>
>> For AM18xx it could be a simple wrapper driver that just populates the children?
> 
> I suppose that could work. I will look into it (perhaps after seeing what you
> come up with in v2).
> 
>>
>>>
>>>> +- #address-cells : should be 1
>>>> +- #size-cells    : should be 1
>>>> +- ranges         : standard ranges definition
>>>> +
>>>
>>> ...
>>>
>>>> +
>>>> +PRUSS INTC Child Node
>>>> +======================
>>>> +Each PRUSS has a single interrupt controller instance that is common to both
>>>> +the PRU cores. Each interrupt controller can detect 64 input events which are
>>>> +then mapped to 10 possible output interrupts through two levels of mapping. The
>>>> +input events can be triggered by either the PRUs and/or various other PRUSS
>>>> +internal and external peripherals. The first 2 output interrupts are fed
>>>> +exclusively to the internal PRU cores, with the remaining 8 connected to
>>>> +external interrupt controllers including the MPU.
>>>
>>> FYI, on AM18xx, there is a PRUSSEVTSEL bit in CFGCHIP3[3] (already a syscon node
>>> in the device tree) that allows selecting one of two groups of 32 input events
>>> out of this group of 64. This is perhaps getting out of the scope of this patch
>>> series, but I just want to make sure we end up with something that can be easily
>>> extended for this case. For example, I was thinking that this binding could be
>>> modified so that #interrupt-cells could be 1 or 2. If it is 2, then the first
>>> cell specifies the PRUSSEVTSEL value and the second value is the event number.
>>>
>>
>> this is da850.dtsi correct?
> 
> Yes.
> 
>>
>> As PRUSSEVTSEL is not SYSEVENT specific but applies to all the SYSEVENTs at a time.
>> I don't think interrupt-cells is the right place to specify this.
>>
>> Can it be set in DT in the board file? But this can't change once booted so maybe restrictive.
> 
> I guess the way I see this is that it is like specifying the bank and index for
> a GPIO. If you only specify the system event number, then it is not clear which
> event you mean - it could be one of two events. You have to also specify the
> PRUSSEVTSEL value (one could call this the bank or group, I suppose) to fully
> describe the system event.

But this PRUSSEVTSEL is not present on most SoCs. I think it is only on the AM18xx and OMAP-L13x SoCs.

How about modelling this as a linear map of 64 events and decode this internally in INTC driver.
i.e. 0 to 31 set PRUSSEVTSEL to 0 and 32 to 63 set PRUSSEVTSEL to 1.

If any interrupt map provides sysevents from both groups simultaneously then we complain and error out.

This should keep the dt-binding and resource table format identical across all SoCs.

> 
>>
>> If runtime change is required it can only be done before a PRU boots.
>>
>> How about providing this info in the resource table and/or application DT node?
> 
> This seems like this would make it easy to end up with a broken interrupts
> if you accidentally try to use interrupts from both groups. Instead this
> could be implemented in the irqchip driver such that the first interrupt
> (system event) requested gets to select the group. If any interrupts from
> the other group are requested later, they can just return an error. Any
> interrupts in the same group as the first can be requested successfully.

cheers,
-roger

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