linux-kernel - Re: [PATCH 1/4] dt-bindings: misc: tmr-manager: Add device-tree binding for TMR Manager

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Date:   Thu, 30 Jun 2022 12:07:02 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Rao, Appana Durga Kedareswara" 
        <appana.durga.kedareswara.rao@....com>,
        "Simek, Michal" <michal.simek@....com>,
        Appana Durga Kedareswara rao <appana.durga.rao@...inx.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "derek.kiernan@...inx.com" <derek.kiernan@...inx.com>,
        "dragan.cvetic@...inx.com" <dragan.cvetic@...inx.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Cc:     "git (AMD-Xilinx)" <git@....com>, "git@...inx.com" <git@...inx.com>
Subject: Re: [PATCH 1/4] dt-bindings: misc: tmr-manager: Add device-tree
 binding for TMR Manager

On 29/06/2022 14:37, Rao, Appana Durga Kedareswara wrote:
> Hi,
> 
> 
> On 29/06/22 5:29 pm, Michal Simek wrote:
>>
>>
>> On 6/29/22 13:45, Krzysztof Kozlowski wrote:
>>> On 29/06/2022 13:23, Michal Simek wrote:
>>>>
>>>>
>>>> On 6/29/22 12:07, Krzysztof Kozlowski wrote:
>>>>> On 28/06/2022 07:43, Appana Durga Kedareswara rao wrote:
>>>>>> This commit adds documentation for Triple Modular Redundancy(TMR) 
>>>>>> Manager
>>>>>> IP. The Triple Modular Redundancy(TMR) Manager is responsible for 
>>>>>> handling
>>>>>> the TMR subsystem state, including fault detection and error recovery
>>>>>> provides soft error detection, correction and recovery features.
>>>>>>
>>>>>> Signed-off-by: Appana Durga Kedareswara rao 
>>>>>> <appana.durga.rao@...inx.com>
>>>>>> ---
>>>>>>    .../bindings/misc/xlnx,tmr-manager.yaml       | 48 
>>>>>> +++++++++++++++++++
>>>>>
>>>>> This is not a misc device. Find appropriate subsystem for it. It's not
>>>>> EDAC, right?
>>>>
>>>> We were thinking where to put it but it is not EDAC driver.
>>>> If you have better suggestion for subsystem please let us know.
>>>
>>> I don't know what's the device about. The description does not help:
>>>
>>> "TMR Manager is responsible for TMR subsystem state..."
>>
>> ok. let's improve commit message in v2.
> 
> Sure will improve the commit message in v2.
>>
>> TMR - triple module redundancy.
>>
>> You design the system with one CPU which is default microblaze 
>> configuration with interrupt controller, timer and other IPs.
>>
>> And then say I want to do it triple redundant with all that voting, etc.
>> If you want to get all details you can take a look at this guide
>>
>> https://www.xilinx.com/content/dam/xilinx/support/documents/ip_documentation/tmr/v1_0/pg268-tmr.pdf 
>>
>>
>> In short TMR manager is servicing all that 3 cores and making sure that 
>> they are all running in sync. If not it has capability recover the 
>> system. It means cpu gets to break handler (it is the part of microblaze 
>> series) and it restarts all cpus.
>>
>> And TMR inject driver is module which is capable to inject error to 
>> internal memory to cause the exception to exercise that recovery code.
>>
>> Kedar: Feel free to correct me or add more details.
> 
> Thanks Michal for the detailed explanation.
> 
> The Triple Modular Redundancy(TMR) subsystem has three Microblaze 
> processor instances, If any one of the Microblaze processors goes to an 
> unknown state due to fault injection break handler will get called, 
> which in turn calls the tmr manager driver API to perform recovery.
> like Michal said TMR inject driver is capable of inject error to
> internal memory to cause fault in one the Microblaze processor
> 
> @Krzysztof : please let me know if more information required about
> this TMR subsystem will provide.

Some features sound like watchdog. If it was ARM, I would suggest to put
it under "soc". Is a term System-on-Chip applicable to Microblaze? Other
option is to store it under microblaze (although for ARM and RISC-V this
is actually discouraged in favor of soc).

Best regards,
Krzysztof