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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Lada Trimasova <Lada.Trimasova@synopsys.com>,
	"linux-snps-arc@lists.infradead.org"
	<linux-snps-arc@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
	Noam Camus <noamc@ezchip.com>
Subject: Re: [PATCH] arc: use little endian accesses
Date: Fri, 11 Mar 2016 05:18:32 +0000
Message-ID: <C2D7FE5348E1B147BCA15975FBA23075F4E8F5FE@us01wembx1.internal.synopsys.com> (raw)
In-Reply-To: <201603100845.30602.arnd@arndb.de>

On Thursday 10 March 2016 01:15 PM, Arnd Bergmann wrote:
> On Thursday 10 March 2016, Vineet Gupta wrote:
>> On Wednesday 09 March 2016 10:51 PM, Lada Trimasova wrote:
>>> Memory access primitives should use cpu_to_le16, cpu_to_le32, le16_to_cpu
>>> and le32_to_cpu because it is not really guaranteed that drivers handles
>>> any ordering themselves.
>> That is the driver issue. readxx as API simply returns data in native endianness.
>> We've had EZChip running big endian and so far and they didn't need this change.
> Most drivers using readl() or readl_relaxed() expect those to perform byte
> swaps on big-endian architectures, as the registers tend to be fixed endian,
> so the change seems reasonable.
>
> It depends a little bit on how endian mode is implemented in the CPU: do you
> follow the normal model of swapping byte order in the load/store instructions
> of the CPU when running big-endian, or is the CPU always running little-endian
> but the bus addresses get mangled on byte accesses to give the illusion
> of a big-endian system?

OK I got the response from hardware guys that we follow the normal mode of
swapping byte order for big-endian mode. Arnd can u please explain how that might
impact the io accessors, it at all.

And what exactly are semantics of readX() and ioreadX() - even if arch specific
and I'd be glad to change that for ARC.

I can also help with documenting them properly some where as went digging into
mailing list first thing Lada posted this patch :-)

Thx,
-Vineet

      parent reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-09 17:21 Lada Trimasova
2016-03-10  5:05 ` Vineet Gupta
2016-03-10  5:19   ` Vineet Gupta
2016-03-10  5:19     ` Vineet Gupta
2016-03-10  7:44   ` Alexey Brodkin
2016-03-10  9:55     ` Vineet Gupta
2016-03-10 18:57       ` Lada Trimasova
2016-03-10 18:57         ` Lada Trimasova
2016-03-10 19:23         ` Arnd Bergmann
2016-03-11 12:44           ` Vineet Gupta
2016-03-12  4:20             ` Vineet Gupta
2016-03-12  4:20               ` Vineet Gupta
2016-03-11  5:07         ` Noam Camus
2016-03-11  5:07           ` Noam Camus
2016-03-10  7:45   ` Arnd Bergmann
2016-03-10  7:45     ` Arnd Bergmann
2016-03-11  5:18     ` Vineet Gupta [this message]

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