Re: [PATCH v3 6/6] mtd: rawnand: meson: rename node for chip select

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Arseniy,

I'm adding Rafał & Michael: any idea what could be wrong? The behavior
below does not look expected at all, but I thought we (= Rafał, mainly)
already sorted this out?

> >>>>>>> On Wed, May 10, 2023 at 1:13 PM Arseniy Krasnov
> >>>>>>> <AVKrasnov@sberdevices.ru> wrote:      
> >>>>>>>>
> >>>>>>>> This renames node with values for chip select from "reg" to "cs". It is
> >>>>>>>> needed because when OTP access is enabled on the attached storage, MTD
> >>>>>>>> subsystem registers this storage in the NVMEM subsystem. NVMEM in turn
> >>>>>>>> tries to use "reg" node in its own manner, supposes that it has another
> >>>>>>>> layout. All of this leads to device initialization failure.        
> >>>>>>> In general: if we change the device-tree interface (in this case:
> >>>>>>> replacing a "reg" with a "cs" property) the dt-bindings have to be
> >>>>>>> updated as well.      
> >>>>>>
> >>>>>> True, and I would add, bindings should not be broken.      
> >>>>>
> >>>>> I see, that's true. That is bad way to change bindings.
> >>>>>    
> >>>>>>       
> >>>>>>> Documentation/devicetree/bindings/mtd/nand-controller.yaml and
> >>>>>>> Documentation/devicetree/bindings/mtd/amlogic,meson-nand.yaml show
> >>>>>>> that the chip select of a NAND chip is specified with a "reg"
> >>>>>>> property.      
> >>>>>>
> >>>>>> All NAND controller binding expect the chip-select to be in the
> >>>>>> 'reg' property, very much like a spi device would use reg to store the
> >>>>>> cs as well: the reg property tells you how you address the device.
> >>>>>>
> >>>>>> I also fully agree with Martin's comments below. Changing reg is likely
> >>>>>> a wrong approach :)
> >>>>>>       
> >>>>>>> Also the code has to be backwards compatible with old .dtbs.
> >>>>>>>      
> >>>>>>>> Example:
> >>>>>>>>
> >>>>>>>> [...] nvmem mtd0-user-otp: nvmem: invalid reg on /soc/bus@ffe00000/...
> >>>>>>>> [...] mtd mtd0: Failed to register OTP NVMEM device
> >>>>>>>> [...] meson-nand ffe07800.nfc: failed to register MTD device: -22
> >>>>>>>> [...] meson-nand ffe07800.nfc: failed to init NAND chips
> >>>>>>>> [...] meson-nand: probe of ffe07800.nfc failed with error -22        
> >>>>>>> This is odd - can you please share your definition of the &nfc node?      
> >>>>>
> >>>>> Sure, here it is:
> >>>>>
> >>>>> mtd_nand: nfc@7800 {                            
> >>>>> 	compatible = "amlogic,meson-axg-nfc";
> >>>>> 	...
> >>>>> 	nand@0 {                                
> >>>>>         	reg = <0>;
> >>>>>         };
> >>>>> }
> >>>>>
> >>>>> I checked, that 'nand_set_flash_node()' is called with 'nand@0' and i suppose
> >>>>> that it is correct (as You mentioned below). But, 'nvmem_add_cells_from_of()' is called
> >>>>> with parent: 'nfc@7800', then it iterates over its childs, e.g. 'nand@0' and thus i get such
> >>>>> situation. I guess, that 'nvmem_add_cells_from_of()' must be called with 'nand@0' ?    
> >>>>
> >>>> We recently had issues with nvmem parsing, but I believe a mainline
> >>>> kernel should now be perfectly working on this regard. What version of
> >>>> the Linux kernel are you using?    
> >>>
> >>> My current version is:
> >>>
> >>> VERSION = 6                                                             
> >>> PATCHLEVEL = 2                                                          
> >>> SUBLEVEL = 0                                                            
> >>> EXTRAVERSION = -rc8 
> >>>
> >>> Fix was in drivers/nvmem/* ?
> >>>
> >>> Thanks, Arseniy    
> >>
> >> Upd: I resolved problem in the following way:
> >>
> >> nand@0 {                                
> >> 	reg = <0>;//chip select
> >>  
> > 	partitions {
> > 		compatible = ...
> >   
> >> 	otp@0 {                         
> >> 		#address-cells = <2>;   
> >> 		#size-cells = <0>;        
> > 
> > #address/size-cells is not needed here
> >   
> >> 		compatible = "user-otp";
> >> 		reg = <A B>;            
> >> 	};                              
> >> 	otp@1 {                         
> >> 		#address-cells = <2>;   
> >> 		#size-cells = <0>;        
> > 
> > Ditto
> >   
> >> 		compatible = "factory-otp";
> >> 		reg = <C D>;            
> >> 	};                                
> > 
> > 	};
> >   
> >> };
> >>
> >> Now nvmem subsystem parses 'otp@0' and 'otp@1' and error is gone. 'compatible' values are
> >> the same as in drivers/mtd/mtdcore.c:mtd_otp_nvmem_add(). 'reg' in 'nand@0' is used as
> >> chip select as supposed.  
> > 
> > I don't fully get it. The parsing on the nvmem side should not fail if
> > there is no subpartition/otp-region defined. Can you confirm an empty
> > NAND device node works? Because your last e-mail suggested the opposite.  
> 
> Ok, so i'll describe what happens in my case. Let's NAND node be like this (IIUC this is
> considered as empty NAND device):
> 
> mtd_nand: nfc@7800 {                            
> 	compatible = "amlogic,meson-axg-nfc";
> 	...
> 	nand@0 {                                
> 	       	reg = <0>;
> 	};
> }
> 
> I see, that
> 
> 1) 'mtd_otp_nvmem_add()' calls 'mtd_otp_nvmem_register()' twice for two types of
>    OTP memory "user-otp" and "factory-otp". Let's take a look only on "user-otp".
> 2) 'mtd_otp_nvmem_register()' tries to lookup for node in 'nand@0' which is compatible with
>    "user-otp" and then passes found (or not found, e.g. NULL) node to  'nvmem_register()'.
> 3) 'nvmem_register()' uses this node iterating over its childs and searching value "reg" in
>    each child. If "user-otp" node is not found in 2), 'nvmem_register()' uses node 'nfc@7800'
>    also looking for "reg" value in each of its child. In this case it found "reg" in 'nand@0'
>    and fails.
> 
> Now, if i add "compatible = "user-otp";" to 'nand@0', in step 2) search will be successful,
> and "reg" value will be used from this new node (or we remove "reg" from it - nothing happens
> as You wrote). So, problem is that nvmem tries to parse node with invalid "reg" value.
> 
> Also I see, that 'nvmem_register()' is called earlier in 'mtd_nvmem_add()', but with no effect.
> I think, that it is not related with enabled OTP feature.
> 
> Thanks, Arseniy

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