linux-kernel - Re: [PATCH 06/38] Annotate hardware config module parameters in drivers/clocksource/

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Date:   Tue, 18 Apr 2017 18:24:03 +0200
From:   Jens Rottmann <Jens.Rottmann@...INKtech.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        David Howells <dhowells@...hat.com>
CC:     LKML <linux-kernel@...r.kernel.org>, <gnomes@...rguk.ukuu.org.uk>,
        <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        <linux-security-module@...r.kernel.org>,
        <keyrings@...r.kernel.org>, Andres Salomon <dilinger@...ued.net>
Subject: Re: [PATCH 06/38] Annotate hardware config module parameters in
 drivers/clocksource/

Hi,

On 04/14/2017 20:25, Thomas Gleixner wrote:
>>  static int timer_irq;
>> -module_param_named(irq, timer_irq, int, 0644);
>> +module_param_hw_named(irq, timer_irq, int, irq, 0644);
>>  MODULE_PARM_DESC(irq, "Which IRQ to use for the clock source MFGPT ticks.");
> 
> I'm not sure about this. AFAIR the parameter is required to work on
> anything else than some arbitrary hardware which has it mapped to 0.

Parameter defaults to 0, which means:
1. autodetect (=keep IRQ BIOS has set up)
2. if that fails use CONFIG_CS5535_MFGPT_DEFAULT_IRQ
(see drivers/misc/cs5535-mfgpt.c: cs5535_mfgpt_set_irq())

Autodetect works fine for our (ex-LiPPERT, now ADLINK) COTS boards:
Linux auto-uses IRQ chosen in BIOS Setup. Wouldn't know about other
companies, of course, but (2.) means parameter can be avoided via make
menuconfig.

On 04/15/2017 00:59, David Howells wrote:
> Should it then be set through in-kernel platform initialisation
> since the AMD Geode is an embedded chip?

Don't know what each and every of our COTS customers is doing, but I'm
not aware of anyone having written a platform driver. AFAIK many are
running pretty standard distros, e.g. Debian. I happen to have booted
Slackware with a vanilla kernel only a few hours ago.

Cheers,
Jens