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

Thu Jul 21 23:08:00 PDT 2022

On 7/22/22 08:11, Takahiro Kuwano wrote:
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> On 7/22/2022 2:06 PM, Tudor.Ambarus at microchip.com wrote:
>> On 7/22/22 07:46, Takahiro Kuwano wrote:
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>>>
>>> On 7/22/2022 1:20 PM, Tudor.Ambarus at microchip.com wrote:
>>>> On 7/22/22 07:00, Takahiro Kuwano wrote:
>>>>
>>>> Good morning, Takahiro!
>>>>
>>> Good morning, Tudor!
>>>
>>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>>
>>>>> On 7/22/2022 1:06 AM, Tudor.Ambarus at microchip.com wrote:
>>>>>> On 5/23/22 10:49, Michael Walle wrote:
>>>>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>>>>
>>>>>>> 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.
>>>>
>>> It's undetermined. In case we issue Read Any Register with 3B address,
>>> the host controller outputs 4 bytes (opcode + address) then inputs
>>> 1 byte. If the device is in 4B address mode at this time, the host
>>> controller inputs the 1 byte while device is still waits for LSB of
>>> address so IO is not driven by device.
>>>
>>
>> So if the IO lines are floating, we'll "read" whatever is indicated
>> by the IOs at that specific moment of time, right?
>>
> Yes, right.
> 
>> If so, we're forced to statically specify the default internal address
>> mode.
>>
> Yes.
OK, let me scratch something.

-- 
Cheers,
ta