linux-kernel - Re: [PATCH v2 25/25] pmem: convert to generic memremap

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Date:	Sun, 26 Jul 2015 11:11:44 -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>,
	"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>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 25/25] pmem: convert to generic memremap

On Sun, Jul 26, 2015 at 10:33 AM, Christoph Hellwig <hch@....de> wrote:
> On Fri, Jul 24, 2015 at 10:40:20PM -0400, Dan Williams wrote:
>> Update memremap_pmem() to query the architecture for the mapping type of
>> the given persistent memory range  and then pass those flags to generic
>> memremap().  arch_memremap_pmem_flags() is provided an address range to
>> evaluate in the event an arch has a need for different mapping types by
>> address range.  For example the ACPI NFIT carries EFI mapping types in
>> its memory range description table.
>
> I don't think the pmem driver should look at a arch hook here, please
> communicate this through the nvdimm subsystem.
>
> Btw, looking at these changes I also think the __pmem annotations
> are mistake.  We might have all kinds of ways to write to pmem,
> and as long as we properly flush it we don't need to force it
> through the special accessors.  This becomes really interesting
> for PCI DMA access.

I don't follow.  We have __iomem for the cpu mapping of a resource and
dma_map() for a PCI device.  __pmem works the same and is there to
make sure someone doesn't simply de-reference a pointer to pmem and
hope that the write is persistent.
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