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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH] mtd: core: handle flashes without OTP gracefully
To:     Tudor.Ambarus@microchip.com, michael@walle.cc,
        linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com
References: <20210702093841.32307-1-michael@walle.cc>
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 <9F46D75C-D00D-4577-A337-7411049EC7D9@walle.cc>
 <8da3d84e-dfbf-2030-98b4-148362d22f52@microchip.com>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <2716acf0-fcf1-d2ef-83be-152d0300d687@roeck-us.net>
Date:   Sat, 3 Jul 2021 10:26:06 -0700
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On 7/3/21 9:42 AM, Tudor.Ambarus@microchip.com wrote:
> On 7/3/21 7:08 PM, Michael Walle wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>
>> Am 3. Juli 2021 11:56:14 MESZ schrieb Tudor.Ambarus@microchip.com:
>>> On 7/2/21 12:38 PM, Michael Walle wrote:
>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you
>>> know the content is safe
>>>>
>>>> There are flash drivers which registers the OTP callbacks although
>>> the
>>>> flash doesn't support OTP regions and return -ENODATA for these
>>>> callbacks if there is no OTP. If this happens, the probe of the whole
>>>
>>> why do they register the OTP callback if they don't support OTP?
>>
>> I don't know. But I certainly won't touch that code :p
> 
> why? :D
> 
>>
>>
>>>> flash will fail. Fix it by handling the ENODATA return code and skip
>>>> the OTP region nvmem setup.
>>>>
>>>> Fixes: 4b361cfa8624 ("mtd: core: add OTP nvmem provider support")
>>>> Reported-by: Guenter Roeck <linux@roeck-us.net>
>>>> Signed-off-by: Michael Walle <michael@walle.cc>
>>>> ---
>>>>   drivers/mtd/mtdcore.c | 10 ++++++++--
>>>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
>>>> index b5ccd3037788..6881d1423dd6 100644
>>>> --- a/drivers/mtd/mtdcore.c
>>>> +++ b/drivers/mtd/mtdcore.c
>>>> @@ -880,7 +880,10 @@ static int mtd_otp_nvmem_add(struct mtd_info
>>> *mtd)
>>>>
>>>>          if (mtd->_get_user_prot_info && mtd->_read_user_prot_reg) {
>>>>                  size = mtd_otp_size(mtd, true);
>>>> -               if (size < 0)
>>>> +               /* ENODATA means there is no OTP region */
>>>> +               if (size == -ENODATA)
>>>
>>> If no OTP data, maybe it's more appropriate for the clients to just
>>> return a retlen of 0.
>>
>> you mean already checking ENODATA in mtd_otp_size() and return 0. That would also make the hunk below unnecessary. I'll change it.
> 
> I've thought about:
> 
> diff --git a/drivers/mtd/chips/cfi_cmdset_0001.c b/drivers/mtd/chips/cfi_cmdset_0001.c
> index 54f92d09d9cf..9419b33d7238 100644
> --- a/drivers/mtd/chips/cfi_cmdset_0001.c
> +++ b/drivers/mtd/chips/cfi_cmdset_0001.c
> @@ -2314,7 +2314,7 @@ static int cfi_intelext_otp_walk(struct mtd_info *mtd, loff_t from, size_t len,
>   
>          /* Check that we actually have some OTP registers */
>          if (!extp || !(extp->FeatureSupport & 64) || !extp->NumProtectionFields)
> -               return -ENODATA;
> +               return 0;
> 

There are various places where this is called, including code returning information
to userspace. That means you'd be changing the ABI to userspace which would now suddenly
return 0 instead of -ENODATA.

Guenter