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From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Marek Vasut <marex@denx.de>
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 17:01:07 +0100	[thread overview]
Message-ID: <20221202170107.4733efbc@xps-13> (raw)
In-Reply-To: <20221202164904.08d750df@xps-13>


miquel.raynal@bootlin.com wrote on Fri, 2 Dec 2022 16:49:04 +0100:

> Hi Marek,
> 
> marex@denx.de wrote on Fri, 2 Dec 2022 16:23:29 +0100:
> 
> > On 12/2/22 16:00, Miquel Raynal wrote:  
> > > Hi Marek,    
> > 
> > Hi,
> >   
> > > marex@denx.de wrote on Fri, 2 Dec 2022 15:31:40 +0100:
> > >     
> > >> On 12/2/22 15:05, Miquel Raynal wrote:    
> > >>> Hi Francesco,    
> > >>
> > >> Hi,
> > >>
> > >> [...]
> > >>    
> > >>> I still strongly disagree with the initial proposal but what I think we
> > >>> can do is:
> > >>>
> > >>> 1. To prevent future breakages:
> > >>>     Fix fdt_fixup_mtdparts() in u-boot. This way newer U-Boot + any
> > >>>     kernel should work.
> > >>>
> > >>> 2. To help tracking down situations like that:
> > >>>     Keep the warning in ofpart.c but continue to fail.
> > >>>
> > >>> 3. To fix the current situation:
> > >>>      Immediately revert commit (and prevent it from being backported):
> > >>>      753395ea1e45 ("ARM: dts: imx7: Fix NAND controller size-cells")
> > >>>      This way your own boot flow is fixed in the short term.    
> > >>
> > >> Here I disagree, the fix is correct and I think we shouldn't
> > >> proliferate incorrect DTs which don't match the binding document.    
> > > 
> > > I agree we should not proliferate incorrect DTs, so let's use a modern
> > > description then    
> > 
> > Yes please !
> >   
> > > , with a controller and a child node which defines the
> > > chip.    
> > 
> > But what if there is no chip connected to the controller node ?
> > 
> > If I understand the proposal here right (please correct me if I'm wrong), then:  
> 
> Good idea to summarize.
> 
> > 
> > 1) This is the original, old, wrong binding:
> > &gpmi {
> >    #size-cells = <1>;
> >    ...
> >    partition@N { ... };
> > };  
> 
> Yes.
> 
> > 
> > 
> > 2) This is the newer, but still wrong binding:
> > &gpmi {
> >    #size-cells = <0>;
> >    ...
> >    partitions {
> >      partition@N { ... };
> >    };
> > };  
> 
> Well, this is wrong description, but it would work (for compat reasons,
> even though I don't think this is considered valid DT by the schemas).
> 
> > 
> > 3) This is the newest binding, what we want:
> > &gpmi {
> >    #size-cells = <0>;
> >    ...
> >    nand-chip {
> >      partitions {
> >        partition@N { ... };
> >      };
> >    };
> > };  
> 
> Yes

Perhaps I should also mention that #size-cells expected to be 0 has
nothing to do with the "partitions" container (otherwise #address-cells
would be 0 as well). This value is however asking for an address-only
reg property describing which NAND chip should be addressed and how,
basically the NAND controller CS because you can wire your NAND to
any CS.

> > But if there is no physical nand chip connected to the controller, would we end up with empty nand-chip node in DT, like this?
> > &gpmi {
> >    #size-cells = <X>;
> >    ...
> >    nand-chip { /* empty */ };
> > };  
> 
> Is this really a concern? If there is no NAND chip, the controller
> should be disabled, no? I guess technically you could even use the
> status property in the nand-chip node...
> 
> 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
> 
> 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, 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.
> 
> > >> Rather, if a bootloader generates incorrect (new) DT entries, I
> > >> believe the driver should implement a fixup and warn user about this.
> > >> PC does that as well with broken ACPI tables as far as I can tell.
> > >>
> > >> I'm not convinced making a DT non-compliant with bindings again,    
> > > 
> > > I am sorry to say so, but while warnings reported by the tools
> > > should be fixed, it's not because the tool does not scream at you that
> > > the description is valid. We are actively working on enhancing the
> > > schema so that "all" improper descriptions get warnings (see the series
> > > pointed earlier), but in no way this change makes the node compliant
> > > with modern bindings.
> > > 
> > > I'm not saying the fix is wrong, but let's be pragmatic, it currently
> > > leads to boot failures.    
> > 
> > I fully agree that we do have a problem, and that it trickled into stable makes it even worse. Maybe I don't fully understand the thing with nand-chip proposal, see my question above, esp. the last part.
> >   
> > >> only to work around a problem induced by bootloader, is the right approach
> > >> here.    
> > > 
> > > 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.    
> > 
> > Isn't this patch the straight fix, at least until the bootloader can be updated to generate the nand-chip node correctly ?
> >   
> > >> This would be setting a dangerous example, where anyone could request a DT fix to be reverted because their random bootloader does the wrong thing and with valid DT clean up, something broke.    
> > > 
> > > Please, you know this is not valid DT clean up. We've been decoupling
> > > controller and chip description since 2016. What I am proposing is a
> > > valid DT cleanup, not to the latest standard, but way closer than the
> > > current solution.    
> > 
> > I think I really need one more explanation of the nand-chip part above.  
> 
> I hope things are clearer now.
> 
> Thanks,
> Miquèl


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  reply	other threads:[~2022-12-02 16:05 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-02  7:19 [PATCH v1] mtd: parsers: ofpart: Fix parsing when size-cells is 0 Francesco Dolcini
2022-12-02  9:14 ` Miquel Raynal
2022-12-02 10:12   ` Francesco Dolcini
2022-12-02 10:24     ` Francesco Dolcini
2022-12-02 10:53       ` Miquel Raynal
2022-12-02 11:23         ` Francesco Dolcini
2022-12-02 14:05           ` Miquel Raynal
2022-12-02 14:31             ` Marek Vasut
2022-12-02 15:00               ` Miquel Raynal
2022-12-02 15:23                 ` Marek Vasut
2022-12-02 15:49                   ` Miquel Raynal
2022-12-02 16:01                     ` Miquel Raynal [this message]
2022-12-02 16:17                     ` Marek Vasut
2022-12-02 16:42                       ` Miquel Raynal
2022-12-02 16:52                         ` Marek Vasut
2022-12-02 16:57                           ` Miquel Raynal
2022-12-02 17:08                             ` Marek Vasut
2022-12-05 11:26                               ` Francesco Dolcini
2022-12-05 13:49                                 ` Miquel Raynal
2022-12-05 16:25                                   ` Marek Vasut
2022-12-15  7:16                                     ` Miquel Raynal
2022-12-15  7:45                                       ` Marek Vasut
2022-12-15  8:04                                         ` Miquel Raynal
2022-12-16  0:36                                           ` Marek Vasut
2022-12-16  7:52                                             ` Francesco Dolcini
2022-12-16  7:45                                       ` Francesco Dolcini
2022-12-16 10:46                                         ` Marek Vasut
2022-12-16 11:01                                           ` Miquel Raynal
2022-12-16 12:37                                             ` Francesco Dolcini
2022-12-16 13:37                                               ` Miquel Raynal
2022-12-16 14:32                                                 ` Marek Vasut
2022-12-16 15:35                                                   ` Miquel Raynal
2022-12-16 16:30                                                     ` Francesco Dolcini
2023-01-02  9:40                                                       ` Miquel Raynal
2023-01-05 11:33                                                         ` Miquel Raynal
2023-01-05 12:47                                                           ` Francesco Dolcini
2023-01-05 14:51                                                             ` Marek Vasut
2023-01-05 15:03                                                               ` Miquel Raynal
2022-12-02 17:20                         ` Francesco Dolcini
2022-12-05 11:30                           ` Francesco Dolcini
2022-12-05 15:28                             ` Miquel Raynal
2022-12-02 16:45                       ` Francesco Dolcini
2022-12-02 17:05                         ` Miquel Raynal
2022-12-02 15:56               ` Thorsten Leemhuis
2022-12-04 12:50                 ` Marek Vasut
2022-12-04 12:59                   ` Thorsten Leemhuis
2022-12-04 15:50                     ` Marek Vasut
2022-12-02 12:43 ` Greg KH

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