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

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Message-ID: <20230510225359.061c2df6@xps-13>
Date:   Wed, 10 May 2023 22:53:59 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>,
        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

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.

> 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?
> 
> &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;
>         };
>     };
> };
> 
> 
> Best regards,,
> Martin


Thanks,
Miquèl