linux-kernel - Re: [RFC v2 29/39] rtc: add HAS

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Date:   Wed, 1 Jun 2022 13:25:35 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-pci@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@...r.kernel.org>
Subject: Re: [RFC v2 29/39] rtc: add HAS_IOPORT dependencies

On Fri, 29 Apr 2022, Niklas Schnelle wrote:

> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> index 41c65b4d2baf..e1bb11a225b2 100644
> --- a/drivers/rtc/Kconfig
> +++ b/drivers/rtc/Kconfig
> @@ -951,6 +951,7 @@ comment "Platform RTC drivers"
>  config RTC_DRV_CMOS
>  	tristate "PC-style 'CMOS'"
>  	depends on X86 || ARM || PPC || MIPS || SPARC64
> +	depends on HAS_IOPORT

 Umm, I missed this one previously and this is wrong.  We use this driver 
for the DECstation machines (CONFIG_MIPS/CONFIG_MACH_DECSTATION) and those 
do not use (nor indeed have) port I/O as they are TURBOchannel systems and 
they only have a single (memory) address space.  Consequently their DS1287 
chip is memory-mapped (in a linear fashion actually, i.e. there's no 
visible address/data register and individual locations are accessible with 
single CPU instructions), cf. arch/mips/include/asm/mach-dec/mc146818rtc.h 
(that probably ought to be converted to `readb'/`writeb' one day).

 So this has to be sorted differently, perhaps by just:

+	depends on HAS_IOPORT || MACH_DECSTATION

 Note that other machines handled by the MIPS port do use port I/O, cf. 
arch/mips/include/asm/mach-*/mc146818rtc.h.

  Maciej