Re: [PATCH v3 01/11] mtd: cfi_cmdset_0002: Change do_write_oneword() to use chip_good()

[Joakim Tjernlund <Joakim.Tjernlund@xxxxxxxxxxxx>]

On Mon, 2018-11-05 at 11:15 +0100, Boris Brezillon wrote:
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> 
> On Fri, 26 Oct 2018 01:32:09 +0900
> Tokunori Ikegami <ikegami@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > In OpenWrt Project the flash write error caused on some products.
> 
> It's okay to mention that the issue was discovered by the OpenWRT team,
> but I'd rephrase it differently.
> 
> "As reported by the OpenWRT team, write requests sometimes fail on some
> platforms".
> 
> > Also the issue can be fixed by using chip_good() instead of chip_ready().
> > The chip_ready() just checks the value from flash memory twice.
> > And the chip_good() checks the value with the expected value.
> > Probably the issue can be fixed as checked correctly by the chip_good().
> > So change to use chip_good() instead of chip_ready().
> 
> Well, that's not really explaining why you think chip_good() should be
> used instead of chip_ready(). So I went on and looked at the
> chip_good(), chip_ready() and do_write_oneword() implementation, and
> also looked at users of do_write_oneword(). It seems this function is
> used to write data to the flash, and apparently the "one bit should
> toggle to reflect a busy state" does not apply when writing things to
> the memory array (it's probably working for other CFI commands, but I
> guess it takes more time to actually change the level of a NOR cell,
> hence the result of 2 identical reads does not mean that the write is
> done).
> 
> Also, it seems that cmdset_0001 is not implementing chip_ready() the
> same way, and I wonder if cmdset_0002 implementation is correct to
> start with. Or maybe I don't get what chip_ready() is for.
> 
The 0001 cmd set is quite different to 0002 and 0001 is the superior one.
If you look at recent 0002 cmd sets they offer an alternative cmd
set to replace the all the "toggle" ones with something that is
same/similar to what 0001 offers.

 Jocke
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