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

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Message-ID: <mhng-2dc5552b-3c35-4469-b511-3c6dc257b610@palmer-ri-x1c9>
Date: Wed, 05 Feb 2025 07:31:37 -0800 (PST)
From: Palmer Dabbelt <palmer@...belt.com>
To: Conor Dooley <conor@...nel.org>
CC: arikalo@...il.com, linux-riscv@...ts.infradead.org,
  Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu, daniel.lezcano@...aro.org, tglx@...utronix.de,
  djordje.todorovic@...cgroup.com, Dragan.Mladjenovic@...mia.com, linux-kernel@...r.kernel.org
Subject:     Re: [PATCH] riscv: Access time mmio instead of rdtime.

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