linux-kernel - Re: [PATCH] mtd: Make MTD_BCM47XXSFLASH to depend on MIPS

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Message-ID: <20151104185341.GN7274@google.com>
Date:	Wed, 4 Nov 2015 10:53:41 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	Rafał Miłecki <zajec5@...il.com>
Cc:	Javier Martinez Canillas <javier@....samsung.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Luis de Bethencourt <luisbg@....samsung.com>,
	Jeremy Kerr <jk@...abs.org>,
	Neelesh Gupta <neelegup@...ux.vnet.ibm.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Cyril Bur <cyrilbur@...il.com>
Subject: Re: [PATCH] mtd: Make MTD_BCM47XXSFLASH to depend on MIPS

On Wed, Nov 04, 2015 at 10:04:26AM +0100, Rafał Miłecki wrote:
> On 14 October 2015 at 11:04, Javier Martinez Canillas
> <javier@....samsung.com> wrote:
> > The bcm47xxsflash driver uses the KSEG0ADDR() function to map an address
> > to a certain kernel segment. But that is only defined if the MIPS config
> > symbol is enabled. The driver does not have an explicit dependency on it
> > and relies on a transitive dependency relation:
> >
> > MTD_BCM47XXSFLASH -> BCMA_SFLASH -> BCMA_DRIVER_MIPS -> BCMA && MIPS
> >
> > But BCMA_SFLASH and BCMA_DRIVER_MIPS have only runtime and not buildtime
> > dependency with MIPS so can be changed to be built test using the config
> > COMPILE_TEST symbol. But that would make MTD_BCM47XXSFLASH be built with
> > MIPS not enabled and cause the following build error:
> >
> > drivers/mtd/devices//bcm47xxsflash.c: In function 'bcm47xxsflash_read':
> > drivers/mtd/devices//bcm47xxsflash.c:112:2: error: implicit declaration of function 'KSEG0ADDR' [-Werror=implicit-function-declaration]
> >   memcpy_fromio(buf, (void __iomem *)KSEG0ADDR(b47s->window + from),
> 
> I think we're not really supposed to use KSEG0ADDR anyway. What about
> replacing it with ioremap_nocache?

I'm not really a MIPS expert, but isn't KSEG0 actually *cached*? (And is
that correct, then?)

AIUI, ioremap_nocache() will actually get you a KSEG1 address here, I
think.

Also (a bit of a tangent) couldn't "window" be better passed as a second
resource by drivers/bcma/driver_chipcommon_sflash.c? Seems like that
would fit the device/resource model better, and then you wouldn't have
to do any __iomem casts in bcm47xxsflash.c.

Brian
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