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

[Arseniy Krasnov <avkrasnov@sberdevices.ru>]

On 11.05.2023 12:17, Arseniy Krasnov wrote:
> 
> 
> On 11.05.2023 12:12, Miquel Raynal wrote:
>> Hi Arseniy,
>>
>> avkrasnov@sberdevices.ru wrote on Thu, 11 May 2023 11:59:07 +0300:
>>
>>> On 10.05.2023 23:53, Miquel Raynal wrote:
>>>
>>> Hello Martin, Miquel
>>>
>>>> Hi Martin & Arseniy,
>>>>
>>>> martin.blumenstingl@googlemail.com wrote on Wed, 10 May 2023 22:40:37
>>>> +0200:
>>>>   
>>>>> Hello Arseniy,
>>>>>
>>>>> 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

	otp@0 {                         
		#address-cells = <2>;   
		#size-cells = <0>;      
		compatible = "user-otp";
		reg = <A B>;            
	};                              
	otp@1 {                         
		#address-cells = <2>;   
		#size-cells = <0>;      
		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 think, this patch should be abandoned in the next version.

Thanks, Arseniy

> 
>>
>> Thanks,
>> Miquèl

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