Re: [PATCH v1] mtd: parsers: ofpart: Fix parsing when size-cells is 0

From: Marek Vasut <marex@denx.de>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Francesco Dolcini <francesco@dolcini.it>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	linux-mtd@lists.infradead.org,
	Francesco Dolcini <francesco.dolcini@toradex.com>,
	Shawn Guo <shawnguo@kernel.org>,
	linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org,
	u-boot@lists.denx.de
Subject: Re: [PATCH v1] mtd: parsers: ofpart: Fix parsing when size-cells is 0
Date: Fri, 2 Dec 2022 17:52:05 +0100	[thread overview]
Message-ID: <e80377c9-1542-d47d-6d35-2efdc15bcbf8@denx.de> (raw)
In-Reply-To: <20221202174255.2c1cb2ff@xps-13>

On 12/2/22 17:42, Miquel Raynal wrote:
> Hi Marek,

Hi,

[...]

>>> However, it should not be empty, at the very least a reg property
>>> should indicate on which CS it is wired, as expected there:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git/tree/Documentation/devicetree/bindings/mtd/nand-chip.yaml?h=mtd/next
>>
>> OK, I see your point. So basically this?
>>
>> &gpmi {
>>     #size-cells = <1>;
>>     ...
>>     nand-chip@0 {
>>       reg = <0>;
>>     };
>> };
>>
>> btw. the GPMI NAND controller supports only one chipselect, so the reg in nand-chip node makes little sense.
> 
> I randomly opened a reference manual (IMX6DQL.pdf), they say:
> 
> 	"Up to four NAND devices, supported by four chip-selects and one
> 	 ganged ready/ busy."

Doh, and MX7D has the same controller, so size-cells = <1>; makes sense 
with nand-chip@N {} .

> Anyway, the NAND controller generic bindings which require this reg
> property, what the controller or the driver actually supports, or even
> how it is used on current designs is not relevant here.
> 
>>> But, as nand-chip.yaml references mtd.yaml, you can as well use
>>> whatever is described here:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git/tree/Documentation/devicetree/bindings/mtd/mtd.yaml?h=mtd/next
>>>    
>>>> What would be the gpmi controller size cells (X) in that case, still 0, right ? So how does that help solve this problem, wouldn't U-Boot still populate the partitions directly under the gpmi node or into partitions sub-node ?
>>>
>>> The commit that was pointed in the original fix clearly stated that the
>>> NAND chip node was targeted
>>
>> I think this is another miscommunication here. The commit
>>
>> 753395ea1e45 ("ARM: dts: imx7: Fix NAND controller size-cells")
>>
>> modifies the size-cells of the NAND controller. The nand-chip is not involved in this at all . In the examples above, it's the "&gpmi" node size-cells that is modified.
> 
> Yes I know. I was referring to this commit, sorry:
> 36fee2f7621e ("common: fdt_support: add support for "partitions" subnode to fdt_fixup_mtdparts()")
> 
> The log says:
> 
> 	Listing MTD partitions directly in the flash mode has been
> 	deprecated for a while for kernel Device Trees. Look for a node "partitions" in the
> 	found flash nodes and use it instead of the flash node itself for the
> 	partition list when it exists, so Device Trees following the current
> 	best practices can be fixed up.
> 
> Which (I hope) means U-boot will equivalently try to play with the
> partitions container, either in the controller node or in the chip node.
> 
>>> , not the NAND controller node. I hope this
>>> is correctly supported in U-Boot though. So if there is a NAND chip
>>> subnode, I suppose U-Boot would try to create the partitions that are
>>> inside, or even in the sub "partitions" container.
>>
>> My understanding is that U-Boot checks the nand-controller node size-cells, not the nand-chip{} or partitions{} subnode size-cells .
> 
> I don't think U-Boot cares.
> 
>> Francesco, can you please share the DT, including the U-Boot generated partitions, which is passed to Linux on Colibri MX7 ? I think that should make all confusion go away.
> 
> Please also do it with the NAND chip described. If, when the NAND chip
> is described U-Boot tries to create partitions in the controller node,
> then the situation is even worse than I thought. But I believe
> describing the node like a suggest in the DT should prevent the boot
> failure while still allowing a rather good description of the hardware.
> 
> BTW I still think the relevant action right now is to revert the DT
> patch.

I am starting to bank toward that variant as well (thanks for clarifying 
the rationale in the discussion, that helped a lot).

But then, the follow up fix would be what exactly, update the binding 
document to require #size-cells = <1>; ?

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