Re: [PATCH v4 1/2] mtd: spi-nor: Fix whole chip erasing for stacked chips.

[Marek Vasut <marek.vasut@gmail.com>]

On 01/10/2017 06:24 PM, Cyrille Pitchen wrote:
> Hi Marek,
> 
> Le 07/01/2017 à 00:45, Marek Vasut a écrit :
>> On 01/06/2017 06:19 PM, Marcin Krzeminski wrote:
>>> Currently it is possible to disable chip erase for spi-nor driver.
>>> Some modern stacked (multi die) flash chips do not support chip
>>> erase opcode at all but spi-nor framework needs to cope with them too.
>>> This commit extends existing functionality to allow disable
>>> chip erase for a single flash chip.
>>
>> I wonder whether this should really be opt-out flag. Since we'll see
>> more multi-die chips (and chips with different die sizes), I'd say this
>> should rather be opt-in flag.
>>
> 
> Just to be sure I've understood what you propose: do you suggest something
> like CAN_CHIP_ERASE instead of NO_CHIP_ERASE for the new info->flags bit?

Yes

> If so, don't forget that info->flags value is tested for every single entry
> of the spi_nor_ids[] array, including all legacy SPI memories such as AT25
> or M25P80. Currently spi-nor.c calls erase_chip() from spi_nor_erase()
> whenever the user tries to erase the whole memory (len == mtd->size),
> whatever SPI memory is connected to the controller. This implementation is
> not restricted to multi-die memory. Indeed, spi-nor.c is not currently
> aware of multi-die memories.
> 
> Hence if we want an opt-in logic for the new flag and still want to be
> backward compatible, we would have to add the new flag into each entry of
> the spi_nor_ids[] array.

Yeah

> Also I asked Marcin to split his original patch into 2 parts because I
> think there are 2 different topics:
> 
> 1 - disabling chip erase command on memories which don't support this SPI
> command. This is a bug fix: we can still provide this chip erase feature
> using only many regular sector/block erase commands. For sure it is not
> optimal but at least it works hence the bug is fixed.
> 
> Some multi-die memories are examples of devices concerned by the bug but
> maybe they are not the only one. S3AN memories also suffer from this bug
> and it has already been dealt by some Ricardo's patches few weeks ago.
> 
> 2 - adding support to the die erase command: this one is an optimization so
> for me, still useful but with a lower priority as we can still live without
> it so this would let use more time to think about the proper way to
> implement this feature. Also, as Marcin reported, we already have examples
> of multi-die memories which do support the chip erase command.
> 
> Hence it shows us that (chip erase not supported != multi-die).

I agree with this, my point was only about whether we should handle this
as opt-in or out-out .

> Best regards,
> 
> Cyrille
> 
>>> Signed-off-by: Marcin Krzeminski <mar.krzeminski@gmail.com>
>>> ---
>>>  drivers/mtd/spi-nor/spi-nor.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>>> index 2a643a1..595de54 100644
>>> --- a/drivers/mtd/spi-nor/spi-nor.c
>>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>>> @@ -85,6 +85,7 @@ struct flash_info {
>>>  					 * Use dedicated 4byte address op codes
>>>  					 * to support memory size above 128Mib.
>>>  					 */
>>> +#define NO_CHIP_ERASE		BIT(12) /* Chip does not support chip erase */
>>>  };
>>>  
>>>  #define JEDEC_MFR(info)	((info)->id[0])
>>> @@ -1621,6 +1622,8 @@ int spi_nor_scan(struct spi_nor *nor, const char *name, enum read_mode mode)
>>>  		nor->flags |= SNOR_F_USE_FSR;
>>>  	if (info->flags & SPI_NOR_HAS_TB)
>>>  		nor->flags |= SNOR_F_HAS_SR_TB;
>>> +	if (info->flags & NO_CHIP_ERASE)
>>> +		nor->flags |= SNOR_F_NO_OP_CHIP_ERASE;
>>>  
>>>  #ifdef CONFIG_MTD_SPI_NOR_USE_4K_SECTORS
>>>  	/* prefer "small sector" erase if possible */
>>>
>>
>>
> 


-- 
Best regards,
Marek Vasut