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

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Message-ID: <20231117-kindred-manor-863549870bcd@spud>
Date:   Fri, 17 Nov 2023 14:30:00 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Inochi Amaoto <inochiama@...look.com>
Cc:     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.

Cheers,
Conor

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