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

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Message-ID: <6918ed54-3929-4832-1e93-6eb55b75c82b@sberdevices.ru>
Date:   Thu, 11 May 2023 11:59:07 +0300
From:   Arseniy Krasnov <avkrasnov@...rdevices.ru>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     Liang Yang <liang.yang@...ogic.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Yixun Lan <yixun.lan@...ogic.com>, <oxffffaa@...il.com>,
        <kernel@...rdevices.ru>, <linux-mtd@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 6/6] mtd: rawnand: meson: rename node for chip select



On 10.05.2023 23:53, Miquel Raynal wrote:

Hello Martin, Miquel

> Hi Martin & Arseniy,
> 
> martin.blumenstingl@...glemail.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@...rdevices.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@...00000/...
>>> [...] 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@...0 {                            
	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@...0', 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' ?

>>
>> &nfc {
>>       nand_chip0: nand@0 {
>>         reg = <0>;
>>       };
>> };
>>
>> This should result in nand_set_flash_node() being called with
>> &nand_chip0 (if it's called with &nfc then something is buggy in our
>> driver).
>> If there's no child nodes within &nand_chip0 then why would the
>> MTD-to-NVMEM code think that it has to parse something?
>> If you do have child nodes and those are partitions, then make sure
>> that the structure is correct (see the extra "partitions" node inside
>> which all partitions are nested):
>> &nand_chip0 {
>>     partitions {
>>         compatible = "fixed-partitions";
>>         #address-cells = <1>;
>>         #size-cells = <1>;
>>
>>         partition@0 {
>>             label = "u-boot";
>>             reg = <0x0000000 0x4000>;
>>             read-only;
>>         };
>>     };
>> };

No, partition nodes are disabled in this case.

Thanks, Arseniy

>>
>>
>> Best regards,,
>> Martin
> 
> 
> Thanks,
> Miquèl