linux-kernel - Re: [PATCH v2 08/25] arch: introduce memremap()

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Date:	Sun, 26 Jul 2015 10:49:39 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, linux-arch@...r.kernel.org,
	"Kani, Toshimitsu" <toshi.kani@...com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 08/25] arch: introduce memremap()

On Sun, Jul 26, 2015 at 10:25 AM, Christoph Hellwig <hch@....de> wrote:
> On Fri, Jul 24, 2015 at 10:38:42PM -0400, Dan Williams wrote:
>> The behavior change to return NULL on an unsupported request is reserved
>> for a later patch.
>
> Why?

This is for drivers like pmem that care about the mapping type.  For
example, if pmem can't get a cache-enabled mapping it is potentially
putting the write durability of the persistent media at risk.

>> +enum {
>> +     MEMREMAP_WB = 1 << 0,
>> +     MEMREMAP_WT = 1 << 1,
>> +     MEMREMAP_CACHE = MEMREMAP_WB,
>
> What's the point of having this MEMREMAP_CACHE alias?

For developers that are used to seeing ioremap_cache()...

> Also please document the meaning of the flags for the poor users.

Will do.  I'll mostly borrow from the x86 mapping type definitions,
but these will also have architecture specific semantics /
constraints.
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