From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Rob Herring <robh+dt@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>,
Mark Brown <broonie@kernel.org>,
linux-kernel@vger.kernel.org,
Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
Boris Brezillon <boris.brezillon@collabora.com>,
linux-mtd@lists.infradead.org,
Bernhard Frauendienst <kernel@nospam.obeliks.de>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v5 4/4] mtd: Add driver for concatenating devices
Date: Tue, 14 Jan 2020 10:24:32 +0100 [thread overview]
Message-ID: <20200114102432.602415a4@xps13> (raw)
In-Reply-To: <20191209113506.41341ed4@collabora.com>
Hi Rob,
Boris Brezillon <boris.brezillon@collabora.com> wrote on Mon, 9 Dec
2019 11:35:06 +0100:
> On Wed, 27 Nov 2019 11:55:22 +0100
> Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> > Introduce a generic way to define concatenated MTD devices. This may
> > be very useful in the case of ie. stacked SPI-NOR. Partitions to
> > concatenate are described in an additional property of the partitions
> > subnode:
> >
> > flash0 {
> > partitions {
> > compatible = "fixed-partitions";
> > part-concat = <&flash0_part1>, <&flash1_part0>;
> >
> > part0@0 {
> > label = "part0_0";
> > reg = <0x0 0x800000>;
> > };
> >
> > flash0_part1: part1@800000 {
> > label = "part0_1";
> > reg = <0x800000 0x800000>;
>
> So, flash0_part1 and flash0_part2 will be created even though the user
> probably doesn't need them?
>
> > };
> > };
> > };
> >
> > flash1 {
> > partitions {
> > compatible = "fixed-partitions";
> >
> > flash0_part1: part1@0 {
> > label = "part1_0";
> > reg = <0x0 0x800000>;
> > };
> >
> > part0@800000 {
> > label = "part1_1";
> > reg = <0x800000 0x800000>;
> > };
> > };
> > };
>
> IMHO this representation is far from intuitive. At first glance it's not
> obvious which partitions are linked together and what's the name of the
> resulting concatenated part. I definitely prefer the solution where we
> have a virtual device describing the concatenation. I also understand
> that this goes against the #1 DT rule: "DT only decribes HW blocks, not
> how they should be used/configured", but maybe we can find a compromise
> here, like moving this description to the /chosen node?
>
> chosen {
> flash-arrays {
> /*
> * my-flash-array is the MTD name if label is
> * not present.
> */
> my-flash-array {
> /*
> * We could have
> * compatible = "flash-array";
> * but we can also do without it.
> */
> label = "foo";
> flashes = <&flash1 &flash2 ...>;
> partitions {
> /* usual partition description. */
> ...
> };
> };
> };
> };
>
> Rob, what do you think?
Rob, I would really welcome your thoughts on this solution, having
something like a flash-array node in the /chosen/ node would avoid
creating dummy devices, keep the declarations of the physical nodes
tidy and have a very simple description.
Hope this compromise could fit!
>
> >
> > This is useful for boards where memory range has been extended with
> > the use of multiple flash chips as memory banks of a single MTD
> > device, with partitions spanning chip borders.
> >
> > Suggested-by: Bernhard Frauendienst <kernel@nospam.obeliks.de>
> > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Thanks,
Miquèl
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next prev parent reply other threads:[~2020-01-14 9:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-27 10:55 [PATCH v5 0/4] MTD concat Miquel Raynal
2019-11-27 10:55 ` [PATCH v5 1/4] dt-bindings: mtd: Describe MTD partitions concatenation Miquel Raynal
2019-11-27 10:55 ` [PATCH v5 2/4] mtd: concat: Fix a comment referring to an unknown symbol Miquel Raynal
2019-11-27 10:55 ` [PATCH v5 3/4] mtd: Add get_mtd_device_by_node() helper Miquel Raynal
2019-11-27 10:55 ` [PATCH v5 4/4] mtd: Add driver for concatenating devices Miquel Raynal
2019-12-04 9:58 ` Vignesh Raghavendra
2019-12-04 10:17 ` Miquel Raynal
2019-12-04 12:55 ` Vignesh Raghavendra
2019-12-09 10:35 ` Boris Brezillon
2020-01-14 9:24 ` Miquel Raynal [this message]
2020-01-14 17:46 ` Rob Herring
2020-01-14 18:10 ` Miquel Raynal
2020-01-14 21:59 ` Rob Herring
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