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

[Takahiro Kuwano <tkuw584924@gmail.com>]

Any thoughts?

On 5/23/2022 6:56 PM, Takahiro Kuwano wrote:
> 
> 
> 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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