linux-kernel - Re: [PATCH 4/8] tty/serial: add generic serial earlycon

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Date:	Mon, 24 Mar 2014 08:36:46 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH 4/8] tty/serial: add generic serial earlycon

On Mon, Mar 24, 2014 at 6:29 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Monday 24 March 2014 11:22:03 Catalin Marinas wrote:
>> On Fri, Mar 21, 2014 at 09:08:44PM +0000, Rob Herring wrote:
>> > diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
>> > new file mode 100644
>> > index 0000000..241757a
>> > --- /dev/null
>> > +++ b/drivers/tty/serial/earlycon.c
>> [...]
>> > +static void __iomem * __init earlycon_map(unsigned long paddr, size_t size)
>> > +{
>> > +   void __iomem *base;
>> > +#ifdef CONFIG_FIX_EARLYCON_MEM
>> > +   set_fixmap_nocache(FIX_EARLYCON_MEM_BASE, paddr & PAGE_MASK);
>> > +   base = (void __iomem *)__fix_to_virt(FIX_EARLYCON_MEM_BASE);
>> > +   base += paddr & ~PAGE_MASK;
>> > +#else
>> > +   base = ioremap_nocache(paddr, size);
>> > +#endif
>>
>> Just curious why not set_fixmap_io (and plain ioremap)?
>
> Good point. Note that ioremap_nocache() is the same as ioremap()
> on *all* architectures.

I investigated this before adding this to arm64. set_fixmap_io and
set_fixmap_nocache are not the same settings on x86. Whether the
mapping type really matters on x86 or not, I don't know. So I added
the nocache variant to arm64 to avoid a change to x86.

Rob
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