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

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Message-ID: <ae6f0c14-591e-2c98-33f1-fe5ee1e603c4@microchip.com>
Date:   Thu, 26 Nov 2020 12:59:25 +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 v5 1/3] mtd: spi-nor: atmel: remove global protection flag

On 11/26/20 2:45 PM, Tudor Ambarus - M18064 wrote:
> On 11/25/20 8:17 PM, Michael Walle wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>
>> 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
>>
> 
> Right. I think we are both correct, and we should choose one method
> or the other depending on the level of support we want to introduce.
> If we want "locking ops", i.e. partial or full lock and unlock of the
> flash, we'll go your way. If we want to keep things as they were before
> 3e0930f109e76, we'll just support the global unlock by writing 0x00 to SR.

I'm wrong, please ignore. I mixed BP locking with individual sector protection.
Let me read again.