[U-Boot] [PATCH v3] sf: Add auto detection of 4-byte mode (vs standard 3-byte mode)

[Stefan Roese <sr@denx.de>]

Hi Rajat,

On 26.10.18 11:59, Rajat Srivastava wrote:

<snip>

>>  From what I read, Rajat's method is to extend the controller driver to
>> support read SFDP and default to 4-byte mode if supported, or
>> overwritten by user's flag. Stefan's method is to read 4-byte status bit
>> and doesn't change controller driver.
>>
>> Is the default value of this 4-byte status bit valid and correct for all
>> cases?
>>
>> Rajat, without your patch set, does Stefan's solution work for your board?
>>
>> York
> 
> No. Stefan's changes are specific to his boards and is not
> applicable on ours.
> Stefan's patch is to support only certain flash that are factory
> strapped to work in 4-byte addressing modes only and will default
> to old method if such a flash is not found.

That is not 100% correct. The flash does not need to be "factory
strapped" to this 4-byte mode. It needs to be configured to this
4-byte mode. And this is also the case for example, when the ROM
bootloader configures the flash this way or a soft-reboot (without
hard flash chip reset) reboots into U-Boot after the flash was
configured to 4-byte mode in Linux.

And it supports multiple vendors and can easily be extended to
support more. The only thing needed is the detection of the
3-byte vs 4-byte address mode. But please note that it currently
does not actively switch from 3-byte to 4-byte mode. This could
be added though if needed / wanted.

> The flashes on our
> boards (and also other vendor's board) will not work with Stefan's
> patch.
> 
> My patch can handle flashes with address widths of 3-byte, 4-byte
> or both. It also takes a more generic path (as opposed to supporting
> only specific flash models) by parsing SFDP standard parameters and
> then deciding what address width is to be used.

I still don't see why each and every SPI controller driver
needs to be extended to support this SFDP parameter reading. Can't
this be handled by some generic (read common) code part in the
SPI flash infrastructure?

Thanks,
Stefan