Re: [PATCH v15 6/8] mtd: spi-nor: Retain nor->addr_width at 4BAIT parse

[Takahiro Kuwano <tkuw584924@gmail.com>]

On 5/23/2022 4:49 PM, Michael Walle wrote:
> Am 2022-05-14 05:51, schrieb Takahiro Kuwano:
>> On 5/13/2022 6:40 PM, Michael Walle wrote:
>>> [btw the subject still has the old name of the addr_width]
>>>
>> Yes, it must be fixed in next rev.
>>
>>> Am 2022-05-13 03:26, schrieb Takahiro Kuwano:
>>>> On 5/13/2022 7:14 AM, Michael Walle wrote:
>>>>> Am 2022-05-10 00:10, schrieb tkuw584924@gmail.com:
>>>>>> From: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
>>>>>>
>>>>>> In 4BAIT parse, keep nor->params->addr_width because it may be used as
>>>>>> current address mode in SMPT parse later on.
>>>>>
>>>>> Mh I'm not sure this is needed at all.
>>>>>
>>>>> SFDP spec says
>>>>>   Variable address length (the current setting of the address
>>>>>   length mode defines the address length)
>>>>>
>>>>> and
>>>>>   When the length is defined as variable, the software or hardware
>>>>>   controlling the memory is aware of the address length mode last
>>>>>   set in the memory device and this same length of address.
>>>>>
>>>>> We don't set any address mode until all the SFDP parsing is
>>>>> over. Therefore we should always be in 3 byte mode, no?
>>>>>
>>>> Actually there are some devices that have variable address length but
>>>> 4 byte mode by default (I will work on those devices after this series
>>>> is settled). To support such case, I prefer to use params->addr_nbytes
>>>> as current address mode so that I can fix it in post_bfpt_fixup() hook.
>>>
>>> Are there public datasheets available? So these devices have a 3 byte
>> I will send datasheets to you in another email. At this point, only
>> summary datasheet is available in website.
>>
>>> and a 4 byte mode, but after reset, they are in the 4 byte mode? Looks
>> Yes.
>>
>>> like it should be fixed in a different way. I'm not sure the "current
>>> mode" handling is correct.
>>>
>> Yes, we may want to introduce a new flag like SPI_NOR_4BAM_DEFAULT and check
>> the flag in BFPT parse. Once I send another series, please review.
>>
>>> We need to differentiate between the mode the flash currently is using
>>> (nor->addr_nbytes) and the mode parsed by SFDP (params->addr_nbytes).
>>>
>> The flash's address mode affects the address length of Non-4B opcodes,
>> including read/write any register ops used in SMPT parse and Infineon
>> (spansion) specific hooks.
>>
>> The 4B opcodes always take address length of 4 regardless of flash's
>> address mode. In these Infineon chips, 4B opcodes for read/program/
>> erase are available and 4BAIT advertises them. We don't have to enter
>> 4 byte address mode for read/program/erase.
> 
> btw. this is a pity. you are using the stateless 4b opcodes but
> then you don't provide stateless opcodes for the read any register
> op :/
> 
>> So, I think we need to differentiate between address length for
>> read/program/erase and flash's default address mode.
> 
> Or we keep them in sync. E.g. switch to 4bytes mode if we are
> using the 4 byte. Granted, that sounds like a hack :)
> 
Yes, the earlier revision of the series switched to 4byte mode in fixup
hook, but we don't want to change device settings during SFDP parse.

>> Obviously we are using nor->addr_nbytes as address length for read/
>> program/erase and should keep this usage.
> 
> Yes, I wasn't aware that we actually two different runtime
> parameters:
>  - the read/program/erase address width, also used with the
>    4b opcodes
>  - internal mode 3b/4b. Up until now, this wasn't an issue
>    because either the mode was switched or the 4b opcodes
>    were used. So this was mutually exclusive. Now we have
>    flashes which uses 4b opcodes _and_ we need the state
>    of the internal mode.
> 
> I can't think of a good solution for now. Need to think
> more about this, but I'm pretty busy at the moment.
> What I think is clear is that we need two different modes
> here in the spi_nor struct. nor->addr_nbytes for the
> read/program/erase opcodes and nor->address_mode or similar
> which tracks the SPI flash's internal address mode.
> 
So, until we come up with a good solution, can we directly use the address
length of 3 in SMPT parse and vendor specific hooks? By doing that, we can
remove this (6/8) and previous (5/8) patches (minimum change would be
better as a temporary solution).

>> For flash's default address mode, my preference is to use
>> params->addr_nbytes, but I should rename it to something like
>> params->def_addr_nbytes and rework spi_nor_set_addr_nbytes().
> 
> IMHO params should only be used to store the parsed (or
> hardcoded) parameters.
> 
OK, understood.

Thanks,
Takahiro

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