linux-kernel - Re: [PATCH 03/14] rtc: block registration of rtc-cmos when CMOS RTC Not Present

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Date:	Thu, 19 Dec 2013 20:20:54 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	joeyli <jlee@...e.com>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Matt Fleming <matt@...sole-pimps.org>,
	Matthew Garrett <matthew.garrett@...ula.com>, Elliott@...com,
	samer.el-haj-mahmoud@...com, Oliver Neukum <oneukum@...e.de>,
	werner@...e.com, trenn@...e.de, JBeulich@...e.com,
	linux-kernel@...r.kernel.org, rtc-linux@...glegroups.com,
	x86@...nel.org,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 03/14] rtc: block registration of rtc-cmos when CMOS RTC
 Not Present

On 12/19/2013 07:54 PM, joeyli wrote:
> Hi hpa, 
> 
> 於 四，2013-12-19 於 06:38 -0800，H. Peter Anvin 提到：
>> Where did you find a platform with "no CMOS" set and a PNP RTC? I find the expect behavior in that case to be quite ambiguous and it is not at all clear to me that what you have here is the right thing.
> 
> Actually there doesn't have the box both with "No CMOS" and PNP device. 
> I choice to totally block rtc-cmos driver when "No CMOS RTC" because the
> definition in ACPI spec:
> 
> CMOS RTC Not Present
> 
> If set, indicates that the CMOS RTC is either not implemented, or
> does not exist at the legacy addresses. OSPM uses the Control
> Method Time and Alarm Namespace device instead.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> It suggest us using ACPI TAD interface when this flag present. But, I
> agreed your point for this is ambiguous due to ACPI spec didn't clear
> define the relationship between PNP0B0x.
> 
> Maybe we can do more detail check in cmos_init when "No CMOS RTC" set:
>  + check if have ACPI TAD device, then block rtc-cmos
>  + check if no ACPI TAD device, but have PNP0B0x, then we use PNP0b0x.
> 

I think the only thing we should use that bit for is to inhibit the
last-resort probing of I/O ports 0x70-0x73... if at all.

	-hpa


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