linux-kernel - Re: [PATCH v2] clocksource/arm_arch_timer: Fix masking for high freq counters

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Date:   Sun, 08 Aug 2021 11:40:30 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Oliver Upton <oupton@...gle.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Shier <pshier@...gle.com>,
        Raghavendra Rao Ananta <rananta@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>
Subject: Re: [PATCH v2] clocksource/arm_arch_timer: Fix masking for high freq counters

On Sun, 08 Aug 2021 02:14:35 +0100,
Oliver Upton <oupton@...gle.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.