linux-kernel - Re: [RFC PATCH 1/2] memremap: add arch specific hook for MEMREMAP

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Message-ID: <87twkzukup.fsf@belgarion.home>
Date:	Tue, 23 Feb 2016 23:23:42 +0100
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Dan Williams <dan.j.williams@...el.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Nicolas Pitre <nico@...aro.org>
Subject: Re: [RFC PATCH 1/2] memremap: add arch specific hook for MEMREMAP_WB mappings

Dan Williams <dan.j.williams@...el.com> writes:

> On Tue, Feb 23, 2016 at 4:26 AM, Ard Biesheuvel
> <ard.biesheuvel@...aro.org> wrote:
>> On 23 February 2016 at 13:03, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
>>> On 23 February 2016 at 12:58, Russell King - ARM Linux
>>> <linux@....linux.org.uk> wrote:
>>>> On Mon, Feb 22, 2016 at 09:35:24PM +0100, Ard Biesheuvel wrote:
>> OK, I see what you mean. I find it unfortunate that ioremap_cache()
>> instances are blindly being replaced with memremap(), and I wonder if
>> this wasted test by and/or cc'ed to people who can actually test this
>> driver. Dan?

Actually I have the hardware to test it.

And I also know what is behind :
 - it's a CFI NOR based memory
 - these are Intel StrataFlash 28F128J3A chips
 - as a CFI memory it is mapped on the system bus
 - from a read perspective, it behaves like a normal memory
 - but once the first write reaches the CFI, everything changes (the address
   space layout doesn't have the same meaning, be that becoming a status code or
   something else).
   In these conditions reordering of writes versus reads, merging reads after
   a write or coalescing writes is a recipe for disaster.

All of this to say I can make a small discrete number of tests (less than 10
write or erase ones to preserve the precious NOR).

Cheers.

--
Robert