linux-kernel - Re: [RESEND PATCH 2/5] mtd: rawnand: add NVIDIA Tegra NAND Flash controller driver

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Date:   Thu, 31 May 2018 22:30:27 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>, robh+dt@...nel.org,
        dwmw2@...radead.org, computersforpeace@...il.com,
        marek.vasut@...il.com, mark.rutland@....com,
        thierry.reding@...il.com, mturquette@...libre.com,
        sboyd@...nel.org, dev@...xeye.de, richard@....at,
        marcel@...wiler.com, krzk@...nel.org, digetx@...il.com,
        benjamin.lindqvist@...ian.se, jonathanh@...dia.com,
        pdeschrijver@...dia.com, pgaikwad@...dia.com, mirza.krak@...il.com,
        linux-mtd@...ts.infradead.org, linux-tegra@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [RESEND PATCH 2/5] mtd: rawnand: add NVIDIA Tegra NAND Flash
 controller driver

On Thu, 31 May 2018 19:54:08 +0200
Stefan Agner <stefan@...er.ch> wrote:

> >> +
> >> +	mtd->dev.parent = &pdev->dev;
> >> +	mtd->name = "tegra_nand";  
> > 
> > I just figured it was undocumented (yet) but you could have a label
> > string property in your nand DT node that tells you the name of the
> > MTD device instead of something too generic like tegra_nand.
> >   
> 
> Using label in the NAND chip subnode actually causes current U-Boot to
> delete (!!) the chip node and create partitions on the controller node.
> 
> See:
> https://elixir.bootlin.com/u-boot/latest/source/common/fdt_support.c#L757
> 
> The code essentially uses the property label to detect whether its a
> NAND chip or a partition...

Why not fixing that in uboot? The representation where the NAND device
and NAND controller are mixed in a single node called nand@xxx is just
wrong from a HW PoV, and it seems uboot is using this representation,
which is probably why you have a problem when trying to find the
partition directly under the NAND controller node.

> 
> At least this is the case when using fdt_fixup_mtdparts and passing the
> controller compatible ("nvidia,tegra20-nand") in node_info,

Just a digression, but I recommend using
"nvidia,tegra20-nand-controller" for the compatible, because the node
is describing the NAND controller not the NAND chip. 

> what our
> downstream U-Boot is currently doing. Maybe we should pass the
> compatible property of the NAND chip?

Or maybe you should search for partitions in children of the controller
node instead of searching directly under the controller node itself.

> But afaik, chips do not have a
> compatible necessarily.

Nope, and it should stay like that.

> 
> So using label in the chip node is currently a no-go for me.

I hope I'm wrong but I fear this is not the only problem you'll face
when switching to a controller+chip representation. This is just the
tip of the iceberg.

> 
> Will send out v3 soon.

Sure, let's see how v3 looks.