Re: [RFC PATCH] mtd: add OTP (one-time-programmable) erase ioctl

[Michael Walle <michael@walle.cc>]

Am 2021-03-02 16:30, schrieb Vignesh Raghavendra:
> Hi,
> 
> On 3/2/21 4:39 PM, Michael Walle wrote:
>> This may sound like a contradiction but some SPI-NOR flashes really
>> support erasing their OTP region until it is finally locked. Having 
>> the
>> possibility to erase an OTP region might come in handy during
>> development.
>> 
>> The ioctl argument follows the OTPLOCK style.
>> 
>> Signed-off-by: Michael Walle <michael@walle.cc>
>> ---
>> OTP support for SPI-NOR flashes may be merged soon:
>> https://lore.kernel.org/linux-mtd/20210216162807.13509-1-michael@walle.cc/
>> 
>> Tudor suggested to add support for the OTP erase operation most 
>> SPI-NOR
>> flashes have:
>> https://lore.kernel.org/linux-mtd/d4f74b1b-fa1b-97ec-858c-d807fe1f9e57@microchip.com/
>> 
>> Therefore, this is an RFC to get some feedback on the MTD side, once 
>> this
>> is finished, I can post a patch for mtd-utils. Then we'll have a 
>> foundation
>> to add the support to SPI-NOR.
>> 
>>  drivers/mtd/mtdchar.c      |  7 ++++++-
>>  drivers/mtd/mtdcore.c      | 12 ++++++++++++
>>  include/linux/mtd/mtd.h    |  3 +++
>>  include/uapi/mtd/mtd-abi.h |  2 ++
>>  4 files changed, 23 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
>> index 323035d4f2d0..da423dd031ae 100644
>> --- a/drivers/mtd/mtdchar.c
>> +++ b/drivers/mtd/mtdchar.c
>> @@ -661,6 +661,7 @@ static int mtdchar_ioctl(struct file *file, u_int 
>> cmd, u_long arg)
>>  	case OTPGETREGIONCOUNT:
>>  	case OTPGETREGIONINFO:
>>  	case OTPLOCK:
>> +	case OTPERASE:
> 
> This is not a Safe IOCTL. We are destroying OTP data. Need to check for
> write permission before allowing the ioctl right?

Ah yes, of course. But this makes me wonder why OTPLOCK
is considered a safe command. As well as MEMLOCK and
MEMUNLOCK. And MEMSETBADBLOCK. Shouldn't these also
require write permissions?

>>  	case ECCGETLAYOUT:
>>  	case ECCGETSTATS:
>>  	case MTDFILEMODE:
>> @@ -938,6 +939,7 @@ static int mtdchar_ioctl(struct file *file, u_int 
>> cmd, u_long arg)
>>  	}
>> 
>>  	case OTPLOCK:
>> +	case OTPERASE:
>>  	{
>>  		struct otp_info oinfo;
>> 
>> @@ -945,7 +947,10 @@ static int mtdchar_ioctl(struct file *file, u_int 
>> cmd, u_long arg)
>>  			return -EINVAL;
>>  		if (copy_from_user(&oinfo, argp, sizeof(oinfo)))
>>  			return -EFAULT;
>> -		ret = mtd_lock_user_prot_reg(mtd, oinfo.start, oinfo.length);
>> +		if (cmd == OTPLOCK)
>> +			ret = mtd_lock_user_prot_reg(mtd, oinfo.start, oinfo.length);
>> +		else
>> +			ret = mtd_erase_user_prot_reg(mtd, oinfo.start, oinfo.length);
>>  		break;
>>  	}
>> 
>> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
>> index 2d6423d89a17..d844d718ef77 100644
>> --- a/drivers/mtd/mtdcore.c
>> +++ b/drivers/mtd/mtdcore.c
>> @@ -1918,6 +1918,18 @@ int mtd_lock_user_prot_reg(struct mtd_info 
>> *mtd, loff_t from, size_t len)
>>  }
>>  EXPORT_SYMBOL_GPL(mtd_lock_user_prot_reg);
>> 
>> +int mtd_erase_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t 
>> len)
>> +{
>> +	struct mtd_info *master = mtd_get_master(mtd);
>> +
>> +	if (!master->_erase_user_prot_reg)
>> +		return -EOPNOTSUPP;
>> +	if (!len)
>> +		return 0;
>> +	return master->_erase_user_prot_reg(master, from, len);
>> +}
>> +EXPORT_SYMBOL_GPL(mtd_erase_user_prot_reg);
>> +
>>  /* Chip-supported device locking */
>>  int mtd_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
>>  {
>> diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
>> index 157357ec1441..734ad7a8c353 100644
>> --- a/include/linux/mtd/mtd.h
>> +++ b/include/linux/mtd/mtd.h
>> @@ -336,6 +336,8 @@ struct mtd_info {
>>  				     size_t len, size_t *retlen, u_char *buf);
>>  	int (*_lock_user_prot_reg) (struct mtd_info *mtd, loff_t from,
>>  				    size_t len);
>> +	int (*_erase_user_prot_reg) (struct mtd_info *mtd, loff_t from,
>> +				     size_t len);
>>  	int (*_writev) (struct mtd_info *mtd, const struct kvec *vecs,
>>  			unsigned long count, loff_t to, size_t *retlen);
>>  	void (*_sync) (struct mtd_info *mtd);
>> @@ -517,6 +519,7 @@ int mtd_read_user_prot_reg(struct mtd_info *mtd, 
>> loff_t from, size_t len,
>>  int mtd_write_user_prot_reg(struct mtd_info *mtd, loff_t to, size_t 
>> len,
>>  			    size_t *retlen, u_char *buf);
>>  int mtd_lock_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t 
>> len);
>> +int mtd_erase_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t 
>> len);
>> 
>>  int mtd_writev(struct mtd_info *mtd, const struct kvec *vecs,
>>  	       unsigned long count, loff_t to, size_t *retlen);
>> diff --git a/include/uapi/mtd/mtd-abi.h b/include/uapi/mtd/mtd-abi.h
>> index 65b9db936557..242015f60d10 100644
>> --- a/include/uapi/mtd/mtd-abi.h
>> +++ b/include/uapi/mtd/mtd-abi.h
>> @@ -205,6 +205,8 @@ struct otp_info {
>>   * without OOB, e.g., NOR flash.
>>   */
>>  #define MEMWRITE		_IOWR('M', 24, struct mtd_write_req)
>> +/* Erase a given range of user data (must be in mode 
>> %MTD_FILE_MODE_OTP_USER) */
>> +#define OTPERASE		_IOR('M', 25, struct otp_info)
>> 
> 
> Hmm, shouldn't this be:
> 
> #define OTPERASE		_IOW('M', 25, struct otp_info)
> 
> Userspace is writing struct otp_info to the driver. OTPLOCK should
> probably be _IOW() as well.

You're right.

NB. most OTP commands have a wrong direction flag.

>>  /*
>>   * Obsolete legacy interface. Keep it in order not to break userspace
>> 

-michael