linux-kernel - Re: [Linux-nvdimm] [PATCH v2] pmem: Initial version of persistent memory driver

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Date:	Tue, 9 Sep 2014 09:53:52 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Boaz Harrosh <boaz@...xistor.com>
Cc:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Jens Axboe <axboe@...nel.dk>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Nick Piggin <npiggin@...nel.dk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-nvdimm@...ts.01.org
Subject: Re: [Linux-nvdimm] [PATCH v2] pmem: Initial version of persistent
 memory driver

On Tue, Sep 9, 2014 at 9:23 AM, Boaz Harrosh <boaz@...xistor.com> wrote:
> From: Ross Zwisler <ross.zwisler@...ux.intel.com>
>
> PMEM is a new driver that presents a reserved range of memory as a
> block device.  This is useful for developing with NV-DIMMs, and
> can be used with volatile memory as a development platform.
>
> [boaz]
> SQUASHME: pmem: Remove unused #include headers
> SQUASHME: pmem: Request from fdisk 4k alignment
> SQUASHME: pmem: Let each device manage private memory region
> SQUASHME: pmem: Support of multiple memory regions
>
> The API to pmem module a single string parameter named "map"
> of the form:
>                  map=mapS[,mapS...]
>
>                  where mapS=nn[KMG]$ss[KMG],
>                  or    mapS=nn[KMG]@ss[KMG],
>
>                  nn=size, ss=offset
>
> Just like the Kernel command line map && memmap parameters,
> so anything you did at grub just copy/paste to here.
>
> The "@" form is exactly the same as the "$" form only that
> at bash prompt we need to escape the "$" with \$ so also
> support the '@' char for convenience.

Hmm this looks like a "ACPI/DeviceTree-over-kernel-command-line"
description language.  I understand that this is borrowed from the
memmap= precedent, but, if I'm not mistaken, that's really more for
debug rather than a permanent platform-device descriptor.  <strawman>
Since this looks like firmware why not go ahead and use
request_firmware() to request a pmem range descriptor blob</strawman>?
 Given you can compile such a blob into a kernel image  or provide it
in an initrd I think it makes deployment more straightforward, also
the descriptor format can be extended going forward whereas the
command line approach mandates ever increasingly complicated strings.
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