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

[Tudor.Ambarus at microchip.com]

On 7/22/22 07:00, Takahiro Kuwano wrote:

Good morning, Takahiro!

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> On 7/22/2022 1:06 AM, Tudor.Ambarus at microchip.com wrote:
>> On 5/23/22 10:49, Michael Walle wrote:
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>>>
>>> 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 at gmail.com:
>>>>>>>> From: Takahiro Kuwano <Takahiro.Kuwano at 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 :)
>>>
>>>> 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.
>>
>> Hi, Takahiro,
>>
>> Can we determine the flash's internal address mode by querying
>> the flash at run-time? Is this possible on Semper flashes?
>>
> CFR2V[7] has current address mode, but to read that, we need to
> issue Read Any Register which address length relies on current
> address mode. Chicken-and-egg...
> 

I see. What happens if we issue the Read Any Register command with
the wrong address internal mode? Will I read just 0xff?
For example try reading CFR2V[7] using addr_nbytes of value 3, and
if it fails, to read it again but this time using addr_nbytes of
value 4.

Cheers,
ta


>> To extend the idea, when the flash supports BFPT and defines
>> BFPT_DWORD1_ADDRESS_BYTES_3_ONLY or BFPT_DWORD1_ADDRESS_BYTES_4_ONLY
>> the things are clear, addr_nbytes is fixed.
>> If the flash does not define BFPT or uses
>> BFPT_DWORD1_ADDRESS_BYTES_3_OR_4, then we could determine the addr
>> mode by querying the flash.
>>
>>>
>>>> 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.
>>
>> yep, I share Michael's opinion.
>>
>> Cheers,
>> ta
>>
>>>
>>> -michael
>>>
>>>>  static int spi_nor_set_addr_nbytes(struct spi_nor *nor)
>>>>  {
>>>>       if (nor->flags & SNOR_F_HAS_4BAIT) {
>>>>               nor->addr_nbytes = 4;
>>>>       } else if (nor->params->def_addr_nbytes) {
>>>>               nor->addr_nbytes = nor->params->def_addr_nbytes;
>>>>
>>>>> At some point, the mode is switched and nor->addr_nbytes becomes
>>>>> params->addr_nbytes. It seems in your case nor->addr_nbytes should
>>>>> be 4 right from the beginning. Which also means nor->addr_nbytes
>>>>> should be 3 for the other cases (and probably not 0).
>>>>>
>>>> With param->def_addr_nbytes, I think we can keep nor->addr_nbytes = 0
>>>> during SFDP parse.
>>>>
>>>> Thanks,
>>>> Takahiro
>>