Re: [PATCH v3] mtd: limit OTP NVMEM Cell parse to non Nand devices

[Miquel Raynal]

Hi Christian,

ansuelsmth@xxxxxxxxx wrote on Wed, 27 Mar 2024 15:36:54 +0100:

> On Wed, Mar 27, 2024 at 03:26:55PM +0100, Rafał Miłecki wrote:
> > On 2024-03-22 05:09, Christian Marangi wrote:  
> > > MTD OTP logic is very fragile and can be problematic with some specific
> > > kind of devices.
> > > 
> > > NVMEM across the years had various iteration on how Cells could be
> > > declared in DT and MTD OTP probably was left behind and
> > > add_legacy_fixed_of_cells was enabled without thinking of the
> > > consequences.  
> > 
> > Er... thank you?
> >  
> 
> Probably made some bad assumption and sorry for it!

Well, "not thinking about all consequences" seems always legitimate to
me, we are not robots. Anyway, I agree we should drop this sentence.

> > > That option enables NVMEM to scan the provided of_node and treat each
> > > child as a NVMEM Cell, this was to support legacy NVMEM implementation
> > > and don't cause regression.
> > > 
> > > This is problematic if we have devices like Nand where the OTP is
> > > triggered by setting a special mode in the flash. In this context real
> > > partitions declared in the Nand node are registered as OTP Cells and
> > > this cause probe fail with -EINVAL error.
> > > 
> > > This was never notice due to the fact that till now, no Nand supported
> > > the OTP feature. With commit e87161321a40 ("mtd: rawnand: macronix: OTP
> > > access for MX30LFxG18AC") this changed and coincidentally this Nand is
> > > used on an FritzBox 7530 supported on OpenWrt.  
> > 
> > So as you noticed this problem was *exposed* by adding OTP support for
> > Macronix NAND chips.
> > 
> >   
> > > Alternative and more robust way to declare OTP Cells are already
> > > prossible by using the fixed-layout node or by declaring a child node
> > > with the compatible set to "otp-user" or "otp-factory".
> > > 
> > > To fix this and limit any regression with other MTD that makes use of
> > > declaring OTP as direct child of the dev node, disable
> > > add_legacy_fixed_of_cells if we detect the MTD type is Nand.
> > > 
> > > With the following logic, the OTP NVMEM entry is correctly created with
> > > no Cells and the MTD Nand is correctly probed and partitions are
> > > correctly exposed.
> > > 
> > > Fixes: 2cc3b37f5b6d ("nvmem: add explicit config option to read old
> > > syntax fixed OF cells")  
> > 
> > It's not that commit however that introduced the problem. Introducing
> > "add_legacy_fixed_of_cells" just added a clean way of enabling parsing
> > of old cells syntax. Even before my commit NVMEM subsystem was looking
> > for NVMEM cells in NAND devices.
> > 
> > I booted kernel 6.6 which has commit e87161321a40 ("mtd: rawnand:
> > macronix: OTP > access for MX30LFxG18AC") but does NOT have commit
> > 2cc3b37f5b6d ("nvmem: add explicit config option to read old syntax
> > fixed OF cells").
> > 
> > Look at this log from Broadcom Northstar (Linux 6.6):
> > [    0.410107] nand: device found, Manufacturer ID: 0xc2, Chip ID: 0xdc
> > [    0.416531] nand: Macronix MX30LF4G18AC
> > [    0.420409] nand: 512 MiB, SLC, erase size: 128 KiB, page size: 2048, OOB
> > size: 64
> > [    0.428022] iproc_nand 18028000.nand-controller: detected 512MiB total,
> > 128KiB blocks, 2KiB pages, 16B OOB, 8-bit, BCH-8
> > [    0.438991] Scanning device for bad blocks
> > [    0.873598] Bad eraseblock 738 at 0x000005c40000
> > [    1.030279] random: crng init done
> > [    1.854895] Bad eraseblock 2414 at 0x000012dc0000
> > [    2.657354] Bad eraseblock 3783 at 0x00001d8e0000
> > [    2.662967] Bad eraseblock 3785 at 0x00001d920000
> > [    2.848418] nvmem user-otp1: nvmem: invalid reg on
> > /nand-controller@18028000/nand@0
> > [    2.856126] iproc_nand 18028000.nand-controller: error -EINVAL: Failed to
> > register OTP NVMEM device
> > 
> > So to summary it up:
> > 1. Problem exists since much earlier and wasn't introduced by 2cc3b37f5b6d
> > 2. Commit 2cc3b37f5b6d just gives you a clean way of solving this issue
> > 3. Problem was exposed by commit e87161321a40
> > 4. We miss fix for v6.6 which doesn't have 2cc3b37f5b6d (it hit v6.7)
> >   
> 
> So the thing was broken all along? Maybe the regression was introduced
> when OF support for NVMEM cell was introduced? (and OF scan was enabled
> by default?)
> 
> Anyway Sorry for adding the wrong fixes, maybe Miquel can remote the
> commit from mtd/fixes and fix the problematic fixes tag?

Yes, please send a v4 (with the sentence above updated) and I will drop
v3.

Thanks,
Miquèl