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

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Francesco Dolcini <francesco@dolcini.it>
Cc: Marek Vasut <marex@denx.de>, 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 14:49:17 +0100	[thread overview]
Message-ID: <20221205144917.6514168a@xps-13> (raw)
In-Reply-To: <Y43VdPftDbq6cD2L@francesco-nb.int.toradex.com>

Hi Francesco,

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...), 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).

> With all of that said I think that Miquel is right
> 
> > When a patch breaks a board and there is no straight fix, you revert
> > it, then you think harder. That's what I am saying. This is a temporary
> > solution.  
> 
> ?
> 
> Francesco
> 
> 

Thanks,
Miquèl

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