linux-kernel - Re: [PATCH v3 28/38] rtc: add HAS

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Date:   Mon, 08 May 2023 17:36:31 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-pci@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        linux-rtc@...r.kernel.org
Subject: Re: [PATCH v3 28/38] rtc: add HAS_IOPORT dependencies

On Tue, 2023-03-14 at 13:52 +0100, Alexandre Belloni wrote:
> Hello,
> 
> On 14/03/2023 13:12:06+0100, Niklas Schnelle wrote:
> > In a future patch HAS_IOPORT=n will result in inb()/outb() and friends
> > not being declared. We thus need to add HAS_IOPORT as dependency for
> > those drivers using them.
> > 
> > Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > ---
> >  drivers/rtc/Kconfig | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> > index 5a71579af0a1..20aa77bf0a9f 100644
> > --- a/drivers/rtc/Kconfig
> > +++ b/drivers/rtc/Kconfig
> > @@ -956,6 +956,7 @@ comment "Platform RTC drivers"
> >  config RTC_DRV_CMOS
> >  	tristate "PC-style 'CMOS'"
> >  	depends on X86 || ARM || PPC || MIPS || SPARC64
> > +	depends on HAS_IOPORT
> 
> Did you check that this will not break platforms that doesn't have RTC_PORT defined?
> > 

>From what I can tell the CMOS_READ() macro this driver relies on uses
some form of inb() style I/O port access in all its definitions. So my
understanding is that this device is always accessed via I/O ports even
if the variants differ slightly and would make no sense on a platform
without any way of accessing I/O ports which is what lack of HAS_IOPORT
means. From what I can see even without RTC_PORT being defined the
CMOS_READ is still used. Hope that answers your question?