linux-kernel - Re: [PATCH 2/4] dt-bindings: reserved-memory: Add phram

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Message-ID: <20220311101300.GA32274@axis.com>
Date:   Fri, 11 Mar 2022 11:13:00 +0100
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Rob Herring <robh@...nel.org>
CC:     "vigneshr@...com" <vigneshr@...com>,
        "richard@....at" <richard@....at>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "joern@...ybastard.org" <joern@...ybastard.org>,
        kernel <kernel@...s.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "frowand.list@...il.com" <frowand.list@...il.com>,
        "krzysztof.kozlowski@...onical.com" 
        <krzysztof.kozlowski@...onical.com>
Subject: Re: [PATCH 2/4] dt-bindings: reserved-memory: Add phram

On Thu, Mar 10, 2022 at 09:58:58PM +0100, Rob Herring wrote:
> On Mon, Mar 07, 2022 at 03:15:47PM +0100, Vincent Whitchurch wrote:
> > Add bindings to allow MTD/block devices to be created in reserved-memory
> > regions using the "phram" driver.
> 
> What does 'ph' mean? Please define somewhere for the binding.

Judging from the Kconfig description it means "physical", as in
"physical memory" (as opposed to virtual memory I guess).  I will added
a note in the next version. 

[...]
> > +examples:
> > +  - |
> > +    reserved-memory {
> > +        #address-cells = <1>;
> > +        #size-cells = <1>;
> > +
> > +        phram: flash@...40000 {
> > +            compatible = "phram";
> > +            label = "rootfs";
> 
> That's an odd example...

If it's the "flash" name which is odd for RAM, that's mandated by the
mtd schema.

If it's the "rootfs" label which is odd, I'm not sure I understand why.
I use this feature to pass the rootfs to the kernel when booting from
RAM.  It is much faster and requires less memory than initrd (which is
on top of that being deprecated), and it allows the same disk images to
be used when booting from RAM, unlike initramfs.