linux-kernel - Re: [PATCH] riscv: Access time mmio instead of rdtime.

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Message-ID:
 <AS4PR09MB65189D22F46A6A6CF73325A5F7B42@AS4PR09MB6518.eurprd09.prod.outlook.com>
Date: Wed, 9 Apr 2025 13:00:10 +0000
From: Djordje Todorovic <Djordje.Todorovic@...cgroup.com>
To: Palmer Dabbelt <palmer@...belt.com>, Conor Dooley <conor@...nel.org>
CC: "arikalo@...il.com" <arikalo@...il.com>, "linux-riscv@...ts.infradead.org"
	<linux-riscv@...ts.infradead.org>, Paul Walmsley <paul.walmsley@...ive.com>,
	"aou@...s.berkeley.edu" <aou@...s.berkeley.edu>, "daniel.lezcano@...aro.org"
	<daniel.lezcano@...aro.org>, "tglx@...utronix.de" <tglx@...utronix.de>,
	"Dragan.Mladjenovic@...mia.com" <Dragan.Mladjenovic@...mia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Aleksa
 Paunovic <aleksa.paunovic@...cgroup.com>
Subject: Re: [PATCH] riscv: Access time mmio instead of rdtime.

HTEC Public

Thanks a lot for your feedback. We will address those comments in
the v2 for the change.

Best,
Djordje

________________________________________
From: Palmer Dabbelt <palmer@...belt.com>
Sent: Wednesday, February 5, 2025 4:31 PM
To: Conor Dooley <conor@...nel.org>
Cc: arikalo@...il.com <arikalo@...il.com>; linux-riscv@...ts.infradead.org <linux-riscv@...ts.infradead.org>; Paul Walmsley <paul.walmsley@...ive.com>; aou@...s.berkeley.edu <aou@...s.berkeley.edu>; daniel.lezcano@...aro.org <daniel.lezcano@...aro.org>; tglx@...utronix.de <tglx@...utronix.de>; Djordje Todorovic <djordje.todorovic@...cgroup.com>; Dragan.Mladjenovic@...mia.com <Dragan.Mladjenovic@...mia.com>; linux-kernel@...r.kernel.org <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: Access time mmio instead of rdtime.

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On Sun, 29 Dec 2024 07:09:13 PST (-0800), Conor Dooley wrote:
> On Fri, Dec 27, 2024 at 04:00:56PM +0100, Aleksandar Rikalo wrote:
>> +#if defined(CONFIG_RISCV_TIME_MMIO)
>> +    if (!of_property_read_u64(n, "clock-reg", &mmio_addr)) {
>
> This is a non-standard, undocumented property. reg & reg-names are what
> you should be using here.

We were talking some in the patchwork meeting.  If this system has a
CLINT then it's probably best to refactor the timers such that MMIO
CLINT access is independent from M-mode (as there's some patches
floating around to make M-mode use rdtime on systems that implement
rdtime).

>> +            riscv_time_val = ioremap((long)mmio_addr, 8);
>> +            if (riscv_time_val) {
>> +                    pr_info("Using mmio time register at 0x%llx\n", mmio_addr);
>> +                    static_branch_enable(&riscv_time_mmio_available);
>> +            } else {
>> +                    pr_warn("Unable to use mmio time at 0x%llx\n", mmio_addr);
>> +            }
>> +    }
>> +#endif