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>,
	Francesco Dolcini <francesco@dolcini.it>
Cc: 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: Mon, 5 Dec 2022 17:25:11 +0100	[thread overview]
Message-ID: <ecca019d-b0b7-630c-4221-2684cb51634c@denx.de> (raw)
In-Reply-To: <20221205144917.6514168a@xps-13>

On 12/5/22 14:49, Miquel Raynal wrote:
> Hi Francesco,

Hi,

> francesco@dolcini.it wrote on Mon, 5 Dec 2022 12:26:44 +0100:
> 
>> On Fri, Dec 02, 2022 at 06:08:22PM +0100, Marek Vasut wrote:
>>> But here I would say this is a firmware bug and it might have to be handled
>>> like a firmware bug, i.e. with fixup in the partition parser. I seem to be
>>> changing my opinion here again.
>>
>> I was thinking at this over the weekend, and I came to the following
>> ideas:
>>
>>   - we need some improvement on the fixup we already have in the
>>     partition parser. We cannot ignore the fdt produced by U-Boot - as
>>     bad as it is.
>>   - the proposed fixup is fine for the immediate need, but it is
>>     not going to be enough to cover the general issue with the U-Boot
>>     generated partitions. U-Boot might keep generating partitions as direct
>>     child of the nand controller even when a partitions{} node is
>>     available. In this case the current parser just fails since it looks
>>     only into it and it will find it empty.
>>   - the current U-Boot only handle partitions{} as a direct child of the
>>     nand-controller, the nand-chip is ignored. This is not the way it is
>>     supposed to work. U-Boot code would need to be improved.
> 
> I've been thinking about it this weekend as well and the current fix
> which "just set" s_cell to 1 seems risky for me, it is typically the
> type of quick & dirty fix that might even break other board (nobody
> knew that U-Boot current logic expected #size-cells to be set in the
> DT, what if another "broken" DT expects the opposite...)

Then with the current configuration, such broken DT would not work, 
since current DT does set #size-cells=<1> (wrongly).

> , not
> mentioning potential issues with big storages (> 4GiB).
> 
> All in all, I really think we should revert the DT change now, reverting
> as little to no drawbacks besides a dt_binding_check warning and gives
> us time to deal with it properly (both in U-Boot and Linux).

I am really not happy with this, but if that's marked as intermediate 
fix, go for it.

How do we deal with this in the long run however? Parser-side fix like 
this one, maybe with better heuristics ?

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