linux-kernel - Re: [PATCH v2 5/5] mtd: core: add OTP nvmem provider support

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Message-ID: <5ce79af321eb04e33178b78e4e3f45f0@walle.cc>
Date:   Fri, 02 Jul 2021 11:33:53 +0200
From:   Michael Walle <michael@...le.cc>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: Re: [PATCH v2 5/5] mtd: core: add OTP nvmem provider support

Am 2021-07-02 03:55, schrieb Guenter Roeck:
> On 7/1/21 3:10 PM, Michael Walle wrote:
>> Hi Guenter,
>> 
>> Am 2021-07-01 23:34, schrieb Guenter Roeck:
>>> Hi,
>>> 
>>> On Sat, Apr 24, 2021 at 01:06:08PM +0200, Michael Walle wrote:
>>>> Flash OTP regions can already be read via user space. Some boards 
>>>> have
>>>> their serial number or MAC addresses stored in the OTP regions. Add
>>>> support for them being a (read-only) nvmem provider.
>>>> 
>>>> The API to read the OTP data is already in place. It distinguishes
>>>> between factory and user OTP, thus there are up to two different
>>>> providers.
>>>> 
>>>> Signed-off-by: Michael Walle <michael@...le.cc>
>>> 
>>> This patch causes a boot failure with one of my qemu tests.
>>> With the patch in place, the flash fails to instantiate.
>>> 
>>> [    1.156578] Creating 3 MTD partitions on "physmap-flash":
>>> [    1.157192] 0x000000000000-0x000000040000 : "U-Boot Bootloader"
>>> [    1.184632] 0x000000040000-0x000000060000 : "U-Boot Environment"
>>> [    1.201767] 0x000000060000-0x000000800000 : "Flash"
>>> [    1.222320] Deleting MTD partitions on "physmap-flash":
>>> [    1.222744] Deleting U-Boot Bootloader MTD partition
>>> [    1.303597] Deleting U-Boot Environment MTD partition
>>> [    1.368751] Deleting Flash MTD partition
>>> [    1.430619] physmap-flash: probe of physmap-flash failed with 
>>> error -61
>>> 
>>> -61 is -ENODATA.
>>> 
>>> Other boot tests with different flash chips can still boot.
>>> Reverting this patch (as well as the follow-up patches) fixes
>>> the problem.
>>> 
>>> I do not know if this is a problem with qemu or a problem with the
>>> patch, but, as I mentioned, other flash chips do still instantiate.
>>> 
>>> Do you have an idea what to look for when I try to track down the 
>>> problem ?
>> 
>> I'd start by looking at the return code of mtd_otp_size() because that
>> should be the only function which communicates with the flash at probe
>> time.
>> 
>> Can you share how to reproduce that problem? Like the qemu commandline
>> and involved images?
>> 
> 
> qemu-system-arm -M z2 -kernel arch/arm/boot/zImage -no-reboot \
>     -snapshot -drive file=/tmp/flash,format=raw,if=pflash \
>     --append "root=/dev/mtdblock2 console=ttyS0" \
>     -nographic -monitor null -serial stdio
> 
> This is with qemu v6.0 and pxa_defconfig. The actual flash image 
> doesn't
> really matter (an empty file with a size of 1024*1024*8 bytes is 
> sufficient).

For completeness: with pxa_defconfig, I guess.

> Debugging shows that -ENODATA is reported by cfi_intelext_otp_walk(),
> thanks to:

Thanks for already looking into this.

> 
> [    0.737244] #### FeatureSupport: 0x0 NumProtectionFields: 1
> 
> which seems to suggest that there are indeed flash chips which don't 
> support
> OTP data. With this in mind, is it indeed appropriate to disable 
> support for
> all flash chips which don't support OTP data ?

Yes of course. The SPI NOR drivers doesn't register the callbacks if
there is no OTP support. The others return ENODATA, which I missed.

I'll send a patch shortly.

-michael