linux-kernel - Re: [PATCH v6 15/29] x86/hpet: Add helper function hpet_set_comparator

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Message-ID: <87ilqifhxj.ffs@tglx>
Date:   Fri, 06 May 2022 23:51:52 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        x86@...nel.org
Cc:     Tony Luck <tony.luck@...el.com>, Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH v6 15/29] x86/hpet: Add helper function
 hpet_set_comparator_periodic()

On Fri, May 06 2022 at 23:41, Thomas Gleixner wrote:
> On Thu, May 05 2022 at 16:59, Ricardo Neri wrote:
>> Programming an HPET channel as periodic requires setting the
>> HPET_TN_SETVAL bit in the channel configuration. Plus, the comparator
>> register must be written twice (once for the comparator value and once for
>> the periodic value). Since this programming might be needed in several
>> places (e.g., the HPET clocksource and the HPET-based hardlockup detector),
>> add a helper function for this purpose.
>>
>> A helper function hpet_set_comparator_oneshot() could also be implemented.
>> However, such function would only program the comparator register and the
>> function would be quite small. Hence, it is better to not bloat the code
>> with such an obvious function.
>
> This word salad above does not provide a single reason why the periodic
> programming function is required and better suited for the NMI watchdog
> case and then goes on and blurbs about why a function which is not
> required is not implemented. The argument about not bloating the code
> with an "obvious???" function which is quite small is slightly beyond my
> comprehension level.

What's even more uncomprehensible is that the patch which actually sets
up that NMI watchdog cruft has:

> +       if (hc->boot_cfg & HPET_TN_PERIODIC_CAP)
> +               hld_data->has_periodic = true;

So how the heck does that work with a HPET which does not support
periodic mode?

That watchdog muck will still happily invoke that set periodic function
in the hope that it works by chance?

Thanks,

        tglx