netdev - Re: [RFC 08/15] rtc: at91sam9: Add missing MFD_SYSCON dependency on HAS

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Date:	Thu, 03 Mar 2016 13:58:33 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Sebastian Reichel <sre@...nel.org>,
	David Brown <david.brown@...aro.org>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Lee Jones <lee.jones@...aro.org>,
	Dan Williams <dan.j.williams@...el.com>,
	driverdevel <devel@...verdev.osuosl.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Andy Gross <andy.gross@...aro.org>,
	Linux Media Mailing List <linux-media@...r.kernel.org>,
	Jason Cooper <jason@...edaemon.net>,
	RTCLINUX <rtc-linux@...glegroups.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Marc Zyngier <marc.zyngier@....com>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-soc@...r.kernel.org, Alessandro Zummo <a.zummo@...ertech.it>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	dmaengine@...r.kernel.org, David Woodhouse <dwmw2@...radead.org>
Subject: Re: [RFC 08/15] rtc: at91sam9: Add missing MFD_SYSCON dependency on HAS_IOMEM

On Thursday 03 March 2016 13:27:59 Geert Uytterhoeven wrote:
> On Thu, Mar 3, 2016 at 11:55 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Thursday 03 March 2016 17:03:34 Krzysztof Kozlowski wrote:
> >> index 0da40e2e4280..5c530b6b125d 100644
> >> --- a/drivers/rtc/Kconfig
> >> +++ b/drivers/rtc/Kconfig
> >> @@ -1302,6 +1302,7 @@ config RTC_DRV_AT91RM9200
> >>  config RTC_DRV_AT91SAM9
> >>         tristate "AT91SAM9 RTT as RTC"
> >>         depends on ARCH_AT91 || COMPILE_TEST
> >> +       depends on HAS_IOMEM    # For MFD_SYSCON
> >>         select MFD_SYSCON
> >>         help
> >>           Some AT91SAM9 SoCs provide an RTT (Real Time Timer) block which
> >>
> >
> > This is technically correct, but the entire RTC menu is hidden
> > inside of 'depends on !UML && !S390', so we won't ever get there
> > on any configuration that does not use HAS_IOMEM.
> >
> > If we did, all other RTC drivers would also fail.
> 
> So UML has no RTC. Should/can it use RTC_DRV_GENERIC?

I think nothing should use that, even if it could ;-)

Funny enough, RTC_DRV_GENERIC would probably actually work if you
run UML as root and set iopl() to allow port access, but we don't
really want it to mess with the host RTC.

I don't know where UML gets it real time, but it doesn't actually
need much other than calling clock_gettime(CLOCK_REALTIME, ...)
to get the host time. Presumably it uses some variation of that.

	Arnd