From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Rob Herring <robh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
devicetree@vger.kernel.org, Vignesh Raghavendra <vigneshr@ti.com>,
Tudor Ambarus <Tudor.Ambarus@microchip.com>,
Richard Weinberger <richard@nod.at>,
linux-kernel@vger.kernel.org,
Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
Mark Brown <broonie@kernel.org>,
linux-mtd@lists.infradead.org,
Bernhard Frauendienst <kernel@nospam.obeliks.de>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
Boris Brezillon <boris.brezillon@collabora.com>
Subject: Re: [PATCH v4 3/4] dt-bindings: mtd: Describe mtd-concat devices
Date: Mon, 25 Nov 2019 15:15:23 +0100 [thread overview]
Message-ID: <20191125151523.0766b3b7@xps13> (raw)
In-Reply-To: <20191118221341.GA30937@bogus>
Hi Rob,
Rob Herring <robh@kernel.org> wrote on Mon, 18 Nov 2019 16:13:41 -0600:
> On Wed, Nov 13, 2019 at 06:15:04PM +0100, Miquel Raynal wrote:
> > From: Bernhard Frauendienst <kernel@nospam.obeliks.de>
> >
> > The main use case to concatenate MTD devices is probably SPI-NOR
> > flashes where the number of address bits is limited to 24, which can
> > access a range of 16MiB. Board manufacturers might want to double the
> > SPI storage size by adding a second flash asserted thanks to a second
> > chip selects which enhances the addressing capabilities to 25 bits,
> > 32MiB. Having two devices for twice the size is great but without more
> > glue, we cannot define partition boundaries spread across the two
> > devices. This is the gap mtd-concat intends to address.
> >
> > There are two options to describe concatenated devices:
> > 1/ One flash chip is described in the DT with two CS;
> > 2/ Two flash chips are described in the DT with one CS each, a virtual
> > device is also created to describe the concatenation.
> >
> > Solution 1/ presents at least 3 issues:
> > * The hardware description is abused;
> > * The concatenation only works for SPI devices (while it could be
> > helpful for any MTD);
> > * It would require a lot of rework in the SPI core as most of the
> > logic assumes there is and there always will be only one CS per
> > chip.
>
> This seems ok if all the devices are identical.
This is not an option for Mark and I agree with him as we are faking
the reality: the two devices we want to virtually concatenate may be
two physically different devices. Binding them as one is lying.
> > Solution 2/ also has caveats:
> > * The virtual device has no hardware reality;
> > * Possible optimizations at the hardware level will be hard to enable
> > efficiently (ie. a common direct mapping abstracted by a SPI
> > memories oriented controller).
>
> Something like this may be necessary if data is interleaved rather than
> concatinated.
This is something that is gonna happen too, it is called "dual
parallel".
> Solution 3
> Describe each device and partition separately and add link(s) from one
> partition to the next
>
> flash0 {
> partitions {
> compatible = "fixed-partitions";
> concat-partition = <&flash1_partitions>;
> ...
> };
> };
>
> flash1 {
> flash1_partition: partitions {
> compatible = "fixed-partitions";
> ...
> };
> };
I honestly don't see how this is different as solution 2/? In one case
we describe the partition concatenation in one subnode as a "link", in
the other we create a separate node to describe the link. Are you
strongly opposed as solution 2/? From a pure conceptual point of view,
is it really different than 3/?
Thanks,
Miquèl
______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
next prev parent reply other threads:[~2019-11-25 14:16 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-13 17:15 [PATCH v4 0/4] MTD concat Miquel Raynal
2019-11-13 17:15 ` [PATCH v4 1/4] mtd: concat: Fix a comment referring to an unknown symbol Miquel Raynal
2020-01-14 17:09 ` Miquel Raynal
2019-11-13 17:15 ` [PATCH v4 2/4] mtd: Add get_mtd_device_by_node() helper Miquel Raynal
2019-11-13 17:15 ` [PATCH v4 3/4] dt-bindings: mtd: Describe mtd-concat devices Miquel Raynal
2019-11-18 22:13 ` Rob Herring
2019-11-25 14:15 ` Miquel Raynal [this message]
2019-12-02 16:26 ` Rob Herring
2019-11-13 17:15 ` [PATCH v4 4/4] mtd: Add driver for concatenating devices Miquel Raynal
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191125151523.0766b3b7@xps13 \
--to=miquel.raynal@bootlin.com \
--cc=Tudor.Ambarus@microchip.com \
--cc=boris.brezillon@collabora.com \
--cc=broonie@kernel.org \
--cc=devicetree@vger.kernel.org \
--cc=kernel@nospam.obeliks.de \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mtd@lists.infradead.org \
--cc=mark.rutland@arm.com \
--cc=paul.kocialkowski@bootlin.com \
--cc=richard@nod.at \
--cc=robh@kernel.org \
--cc=thomas.petazzoni@bootlin.com \
--cc=vigneshr@ti.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).