linux-kernel - Re: [PATCH v4 4/4] mtd: spi-nor: otp: implement erase for Winbond and similar flashes

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Message-ID: <6c8539c4fcfa1e58446826c24fd4e539@walle.cc>
Date:   Tue, 01 Jun 2021 15:30:20 +0200
From:   Michael Walle <michael@...le.cc>
To:     Tudor.Ambarus@...rochip.com
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        p.yadav@...com, miquel.raynal@...tlin.com, richard@....at,
        vigneshr@...com
Subject: Re: [PATCH v4 4/4] mtd: spi-nor: otp: implement erase for Winbond and
 similar flashes

Am 2021-05-31 10:56, schrieb Tudor.Ambarus@...rochip.com:
> On 5/21/21 10:40 PM, Michael Walle wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
>> the content is safe
>> 
>> Winbond flashes with OTP support provide a command to erase the OTP
>> data. This might come in handy during development.
>> 
>> This was tested with a Winbond W25Q32JW on a LS1028A SoC with the
>> NXP FSPI controller.
>> 
>> Signed-off-by: Michael Walle <michael@...le.cc>
>> ---
>>  drivers/mtd/spi-nor/core.c    |  2 +-
>>  drivers/mtd/spi-nor/core.h    |  4 ++
>>  drivers/mtd/spi-nor/otp.c     | 83 
>> +++++++++++++++++++++++++++++++++++
>>  drivers/mtd/spi-nor/winbond.c |  1 +
>>  4 files changed, 89 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
>> index bd2c7717eb10..9551effb6a44 100644
>> --- a/drivers/mtd/spi-nor/core.c
>> +++ b/drivers/mtd/spi-nor/core.c
>> @@ -1318,7 +1318,7 @@ static u32 spi_nor_convert_addr(struct spi_nor 
>> *nor, loff_t addr)
>>  /*
>>   * Initiate the erasure of a single sector
>>   */
>> -static int spi_nor_erase_sector(struct spi_nor *nor, u32 addr)
>> +int spi_nor_erase_sector(struct spi_nor *nor, u32 addr)
>>  {
>>         int i;
>> 
>> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
>> index 28a2e0be97a3..9398a8738857 100644
>> --- a/drivers/mtd/spi-nor/core.h
>> +++ b/drivers/mtd/spi-nor/core.h
>> @@ -207,6 +207,7 @@ struct spi_nor_otp_organization {
>>   * @read:      read from the SPI NOR OTP area.
>>   * @write:     write to the SPI NOR OTP area.
>>   * @lock:      lock an OTP region.
>> + * @erase:     erase an OTP region.
>>   * @is_locked: check if an OTP region of the SPI NOR is locked.
>>   */
>>  struct spi_nor_otp_ops {
>> @@ -214,6 +215,7 @@ struct spi_nor_otp_ops {
>>         int (*write)(struct spi_nor *nor, loff_t addr, size_t len,
>>                      const u8 *buf);
>>         int (*lock)(struct spi_nor *nor, unsigned int region);
>> +       int (*erase)(struct spi_nor *nor, loff_t addr);
> 
> maybe better:
> int (*erase)(struct spi_nor *nor, loff_t addr, size_t len);

Right now these ops represent what is sent to the hardware. The address
is what is really sent over the wire. The read and write has the same
semantics (and limitations, like you can't cross region boundaries etc).

As there is only one kind of method to access OTP right now, I wouldn't
want to prematurely optimize it for future ones. It is easy to change
afterwards if there is need to. And supplying a length right now would
mean to have a loop and some checks in the erase() op; where it should
really be "erase one region" and not "erase multiple ones". Mapping
from multiple to one should be the duty of the otp core code.

So, one could argue about the parameter "unsigned in region" vs.
"loff_t addr" because both represent the same thing. But
spi_nor_otp_erase_secr() should really take the address, because
that is what the opcode takes as an argument. Thus, changing the
argument of the .erase to "unsigned int region" you couldn't just
assign spi_nor_otp_erase_secr to .erase but you'd need to have a
small wrapper which converts the argument.

So IMHO future will tell if we have to change this to somewhat
more generic.

-michael