linux-kernel - Re: [PATCH v6 4/5] mtd: spi-nor: atmel: Fix unlock

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Message-ID: <33b3dd7d-3aa0-2cf2-6f0c-1afaa4dff61d@microchip.com>
Date:   Wed, 2 Dec 2020 10:32:04 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <michael@...le.cc>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <miquel.raynal@...tlin.com>, <richard@....at>, <vigneshr@...com>,
        <boris.brezillon@...labora.com>
Subject: Re: [PATCH v6 4/5] mtd: spi-nor: atmel: Fix unlock_all() for
 AT25FS010/040

On 11/30/20 4:16 PM, Michael Walle wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Am 2020-11-28 09:25, schrieb Tudor.Ambarus@...rochip.com:
>> On 11/26/20 10:26 PM, Michael Walle wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know
>>> the content is safe
>>>
>>> These flashes have some weird BP bits mapping which aren't supported
>>> in
>>> the current locking code. Just add a simple unlock op to unprotect the
>>> entire flash array which is needed for legacy behavior.
>>>
>>> Signed-off-by: Michael Walle <michael@...le.cc>
>>> ---
>>> changes since v5
>>>  - new patch
>>>
>>>  drivers/mtd/spi-nor/atmel.c | 53
>>> +++++++++++++++++++++++++++++++++++--
>>>  drivers/mtd/spi-nor/core.c  |  2 +-
>>>  drivers/mtd/spi-nor/core.h  |  1 +
>>>  3 files changed, 53 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/mtd/spi-nor/atmel.c b/drivers/mtd/spi-nor/atmel.c
>>> index 49d392c6c8bc..fe6a4653823d 100644
>>> --- a/drivers/mtd/spi-nor/atmel.c
>>> +++ b/drivers/mtd/spi-nor/atmel.c
>>> @@ -8,10 +8,59 @@
>>>
>>>  #include "core.h"
>>>
>>> +/*
>>> + * The Atmel AT25FS010/AT25FS040 parts have some weird configuration
>>> for the
>>> + * block protection bits. We don't support them. But legacy behaviour
>>> in linux
>>> + * is to unlock the whole flash array on startup. Therefore, we have
>>> to support
>>> + * exactly this operation.
>>> + */
>>> +static int atmel_at25fs_lock(struct spi_nor *nor, loff_t ofs,
>>> uint64_t len)
>>> +{
>>> +       return -EOPNOTSUPP;
>>> +}
>>> +
>>> +static int atmel_at25fs_unlock(struct spi_nor *nor, loff_t ofs,
>>> uint64_t len)
>>> +{
>>> +       /* We only support unlocking the whole flash array */
>>> +       if (ofs || len != nor->params->size)
>>> +               return -EINVAL;
>>> +
>>> +       /*
>>> +        * Write 0x00 to the status register to try to disable the
>>> write
>>> +        * protection. This will fail if SRWD (the datasheet calls it
>>> WPEN) is
>>> +        * set. But there is nothing we can do.
>>> +        */
>>
>> can't we do the same as you did in 5/5?
> 
> Sure, but - assuming it is only used for the legacy unlock all operation
> - the
> outcome will be the same. It will either keep being locked or all will
> be
> unlocked.

In case WP# is asserted, we'll catch this via the dev_dbg message in
spi_nor_write_sr_and_check() when trying to clear the SRWD bit. We will
have an idea of what's going on, instead of a silent fail to unlock.

> 
> That being said, I can also change it to the same as the
> global_unprotect().
> I don't have any option on that other than this is simpler.
> 
> -michael