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SubjectRe: [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@walle.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

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