linux-kernel - Re: [Linux-nvdimm] another pmem variant

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Date:	Mon, 13 Apr 2015 09:02:54 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Christoph Hellwig <hch@....de>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [Linux-nvdimm] another pmem variant

On Mon, Apr 13, 2015 at 2:01 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Wed, Mar 25, 2015 at 10:00:26AM -0700, Dan Williams wrote:
>> On Wed, Mar 25, 2015 at 9:44 AM, Christoph Hellwig <hch@....de> wrote:
>> > On Wed, Mar 25, 2015 at 09:33:52AM -0700, Dan Williams wrote:
>> >> This is mostly ok and does not collide too much with the upcoming ACPI
>> >> mechanism for this stuff.  I do worry that the new
>> >> "memmap=nn[KMG]!ss[KMG]" kernel command line option will only be
>> >> relevant for at most one kernel cycle given the imminent publication
>> >> of the spec that unblocks our release.
>> >
>> > I don't think we can just get rid of it as legacy systems won't be
>> > upgraded to the new discovery mechanism.  Or do you mean you plan to
>> > introduce a better override on the command line?  In that case speak
>> > up now!
>>
>> The kernel command line would simply be the standard/existing memmap=
>> to reserve a memory range.  Then, when the platform device loads, it
>> does a request_firmware() to inject a binary table that further carves
>> memory into ranges to which the pmem driver attaches.  No need for the
>> legacy system BIOS to be upgraded to the "new way".
>
> Um, what parses that "binary table"?  The kernel better not be doing
> that, as that's not what the firmware interface is for.  The firmware
> interface is for "pass through" only directly to hardware.

I had been using it as a generic/device-model-integrated way to do
what amounts to ACPI table injection [1].  But, now that the new
memmap= command line is upstream, most of the benefits of this
approach are moot and no longer outweigh the downsides [2].  Consider
it tabled.


[1]: https://01.org/linux-acpi/documentation/overriding-dsdt
[2]: http://marc.info/?l=linux-netdev&m=135793331325647&w=2
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