linux-kernel - Re: [PATCH v3 1/2] dt-bindings: timer: thead,c900-aclint-mtimer: separate mtime and mtimecmp regs

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Date:   Sat, 18 Nov 2023 07:25:48 +0800
From:   Inochi Amaoto <inochiama@...look.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Inochi Amaoto <inochiama@...look.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Chen Wang <unicorn_wang@...look.com>,
        Guo Ren <guoren@...nel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v3 1/2] dt-bindings: timer: thead,c900-aclint-mtimer: separate mtime and mtimecmp regs

>
>On Fri, Nov 17, 2023 at 08:30:21PM +0800, Inochi Amaoto wrote:
>>>
>>> On 17/11/2023 06:07, Inochi Amaoto wrote:
>>>> The timer registers of aclint don't follow the clint layout and can
>>>> be mapped on any different offset. As sg2042 uses separated timer
>>>> and mswi for its clint, it should follow the aclint spec and have
>>>> separated registers.
>>>>
>>>> The previous patch introduced a new type of T-HEAD aclint timer which
>>>> has clint timer layout. Although it has the clint timer layout, it
>>>> should follow the aclint spec and uses the separated mtime and mtimecmp
>>>> regs. So a ABI change is needed to make the timer fit the aclint spec.
>>>>
>>>> To make T-HEAD aclint timer more closer to the aclint spec, use
>>>> regs-names to represent the mtimecmp register, which can avoid hack
>>>> for unsupport mtime register of T-HEAD aclint timer.
>>>>
>>>
>>> I don't understand this reasoning. You had one entry, you still have one
>>> entry. Adding reg-names (not regs-names) does not change it.
>>>
>>
>> If no "reg-names", all the register of ACLINT should be defined. However,
>> T-HEAD aclint timer of sg2042 only supports mtimecmp register. If no extra
>> prompt is provided for the SBI, it will fail to recognize aclint timer
>> registers when parsing the aclint node with one reg entry.
>>
>> There is another way to avoid this by using an empty entry to identify
>> unsupported mtime, but Conor have already rejected this. See [1].
>>
>> Link: https://lore.kernel.org/all/20231114-skedaddle-precinct-66c8897227bb@squawk/ [1]
>
>Perhaps you misunderstood my suggestion. I was looking for _both_
>registers to be defined in the binding as well as adding reg-names as a
>required property. Doing what you have here might work for your use
>case, but does not make sense from a bindings point of view as there is
>no way to describe the mtime register, should it exist in another SoC.
>

Thanks for your clarification. If I understand you correctly, the binding
should have all registers that ACLINT has. But for specific use case,
it should only contain supported registers and omit unsupported. Please
correct me if I misunderstood. Thanks.

>Cheers,
>Conor
>