Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sun, 08 Aug 2021 11:40:30 +0100
Message-ID: <87lf5c1aox.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Oliver Upton <oupton@google.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Shier <pshier@google.com>,
        Raghavendra Rao Ananta <rananta@google.com>,
        Ricardo Koller <ricarkol@google.com>
Subject: Re: [PATCH v2] clocksource/arm_arch_timer: Fix masking for high freq counters
In-Reply-To: <CAOQ_QsiECN7iVDyiyos12tk__viGkFhH9b6ZfkZVAYjeKhB=pQ@mail.gmail.com>
References: <20210807191428.3488948-1-oupton@google.com>
        <CACRpkdYPEGygxAtU8jrCtnJsQr_JoYkBCRGpRFpvxGiOzUmxgg@mail.gmail.com>
        <CAOQ_QsiECN7iVDyiyos12tk__viGkFhH9b6ZfkZVAYjeKhB=pQ@mail.gmail.com>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue)
 FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1
 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

On Sun, 08 Aug 2021 02:14:35 +0100,
Oliver Upton <oupton@google.com> wrote:

> The only other sane idea that I could come up with is providing this
> information to the kernel through DT, although that would leave ACPI
> systems behind.

It also has the disadvantage that a large number of DT timer nodes are
a mess of cargo-culted, copy-pasted idioms, and that adding another
property would only make it worse. I'm more confident with something
that can be either:

- checked from EL2 using CNTVOFF, which is complicated, doesn't work
  at EL1, and leaves us in a weird state if we have different counter
  width views in the system (BL is such a wonderful concept)

- or computed from first principle based on the requirements of the
  architecture.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.