linux-kernel - Re: using DMA-API on ARM

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Message-ID: <20141205183113.GD31222@e104818-lin.cambridge.arm.com>
Date:	Fri, 5 Dec 2014 18:31:13 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"brcm80211-dev-list@...adcom.com" <brcm80211-dev-list@...adcom.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arend van Spriel <arend@...adcom.com>,
	David Miller <davem@...emloft.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: using DMA-API on ARM

On Fri, Dec 05, 2014 at 06:24:43PM +0000, Russell King - ARM Linux wrote:
> On Fri, Dec 05, 2014 at 05:38:39PM +0000, Catalin Marinas wrote:
> > On Fri, Dec 05, 2014 at 11:11:14AM +0000, Russell King - ARM Linux wrote:
> > > In any case, wouldn't using a u64 type for "address" be better - isn't
> > > "long long" 128-bit on 64-bit architectures?
> > 
> > No, it's still 64-bit. There is no 128-bit integer in the C standard.
> 
> Actually, that's a fallicy.
> 
> The C99 standard (like previous versions) does not define exactly the
> number of bits in each type.  It defines ranks of type, and says that
> lower ranks are a subrange of integers with higher ranks (for the same
> signed-ness.)  See section 6.2.5.
> 
> So, it merely states that:
> 
> range(char) <= range(short) <= range(int) <= range(long) <= range(long long)

You are probably right, I haven't checked. But the ABI we use in Linux
for 64-bit, LP64, defines long long as 64-bit. Gcc has a int128_t type
but it's specific to this toolchain.

-- 
Catalin
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