linux-kernel - Re: [PATCH v5 1/3] mtd: spi-nor: atmel: remove global protection flag

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Message-ID: <f9724ff71809557283beb7c8c4d4b356@walle.cc>
Date:   Wed, 25 Nov 2020 19:17:57 +0100
From:   Michael Walle <michael@...le.cc>
To:     Tudor.Ambarus@...rochip.com
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 v5 1/3] mtd: spi-nor: atmel: remove global protection flag

Am 2020-11-24 20:09, schrieb Tudor.Ambarus@...rochip.com:
> On 10/3/20 6:32 PM, Michael Walle wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
>> the content is safe
>> 
>> This is considered bad for the following reasons:
>>  (1) We only support the block protection with BPn bits for write
>>      protection. Not all Atmel parts support this.
>>  (2) Newly added flash chip will automatically inherit the "has
>>      locking" support and thus needs to explicitly tested. Better
>>      be opt-in instead of opt-out.
>>  (3) There are already supported flashes which doesn't support
>>      the locking scheme. So I assume this wasn't properly tested
>>      before adding that chip; which enforces my previous argument
>>      that locking support should be an opt-in.
>> 
>> Remove the global flag and add individual flags to all flashes which
>> supports BP locking. In particular the following flashes don't support
>> the BP scheme:
>>  - AT26F004
>>  - AT25SL321
>>  - AT45DB081D
>> 
>> Please note, that some flashes which are marked as SPI_NOR_HAS_LOCK 
>> just
>> support Global Protection, i.e. not our supported block protection
>> locking scheme. This is to keep backwards compatibility with the
>> current "unlock all at boot" mechanism. In particular the following
>> flashes doesn't have BP bits:
>>  - AT25DF041A
>>  - AT25DF321
>>  - AT25DF321A
>>  - AT25DF641
>>  - AT26DF081A
>>  - AT26DF161A
>>  - AT26DF321
>> 
>> Signed-off-by: Michael Walle <michael@...le.cc>
> 
> Reviewed-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> 
>> ---
>> changes since v4:
>>  - none
>> 
>> changes since v3/v2/v1:
>>  - there was no such version because this patch was bundled with 
>> another
>>    patch
>> 
>> changes since RFC:
>>  - mention the flashes which just support the "Global Unprotect" in 
>> the
>>    commit message
>> 
>>  drivers/mtd/spi-nor/atmel.c | 28 +++++++++-------------------
>>  1 file changed, 9 insertions(+), 19 deletions(-)
>> 
>> diff --git a/drivers/mtd/spi-nor/atmel.c b/drivers/mtd/spi-nor/atmel.c
>> index 3f5f21a473a6..49d392c6c8bc 100644
>> --- a/drivers/mtd/spi-nor/atmel.c
>> +++ b/drivers/mtd/spi-nor/atmel.c
>> @@ -10,37 +10,27 @@
>> 
>>  static const struct flash_info atmel_parts[] = {
>>         /* Atmel -- some are (confusingly) marketed as "DataFlash" */
>> -       { "at25fs010",  INFO(0x1f6601, 0, 32 * 1024,   4, SECT_4K) },
>> -       { "at25fs040",  INFO(0x1f6604, 0, 64 * 1024,   8, SECT_4K) },
>> +       { "at25fs010",  INFO(0x1f6601, 0, 32 * 1024,   4, SECT_4K | 
>> SPI_NOR_HAS_LOCK) },
> 
> https://datasheetspdf.com/pdf-file/587164/ATMELCorporation/AT25FS010/1
> BP bits are at bit 2, 3, 5 and 6.
> BP0, BP1, BP3, BP4 and WPEN, are nonvolatile cells
> 
>> +       { "at25fs040",  INFO(0x1f6604, 0, 64 * 1024,   8, SECT_4K | 
>> SPI_NOR_HAS_LOCK) },
> 
> https://datasheetspdf.com/pdf-file/587165/ATMELCorporation/AT25FS040/1
> BP bits are at bit 2, 3, 4, 5, and 6.
> BP0, BP1, BP2, BP3, BP4 are nonvolatile cells
> 
>> 
>> -       { "at25df041a", INFO(0x1f4401, 0, 64 * 1024,   8, SECT_4K) },
>> -       { "at25df321",  INFO(0x1f4700, 0, 64 * 1024,  64, SECT_4K) },
>> -       { "at25df321a", INFO(0x1f4701, 0, 64 * 1024,  64, SECT_4K) },
>> -       { "at25df641",  INFO(0x1f4800, 0, 64 * 1024, 128, SECT_4K) },
>> +       { "at25df041a", INFO(0x1f4401, 0, 64 * 1024,   8, SECT_4K | 
>> SPI_NOR_HAS_LOCK) },
> 
> https://datasheetspdf.com/pdf-file/975331/Adesto/AT25DF041A/1
> Global Protect/Unprotect using Write SR command:
> Global Unlock: write 0x00 to SR
> Global Lock: Read SR. If SR.SPRL is 1 write 0xff to SR, else write 
> 0x7f.

That is not my understanding. Quote:
   To perform a Global Protect, the appropriate WP pin and SPRL
   conditions must be met, and the system must write a logical “1”
   to bits 5, 4, 3, and 2 of the Status Register.

And
   Conversely, to per-form a Global Unprotect, the same WP and SPRL
   conditions must be met but the system must write a logical “0” to
   bits 5, 4, 3, and 2 of the Status Register

Keep in mind that bit 5, 4, 3 and 2 is exactly the
ATMEL_SR_GLOBAL_PROTECT_MASK. The SPRL bit is handled in the unlock()
function. Accoring to table 9.2 you also have to first disable the SPRL
bit and then write the BP bits to zero.

-michael