Re: mtd: cfi: Fixed endless loop problem in CFI when value was written but corrupted.

[Mark Tomlinson <Mark.Tomlinson@xxxxxxxxxxxxxxxxxxx>]

On 19/02/19 9:00 PM, Boris Brezillon wrote:
> On Thu, 14 Feb 2019 00:39:09 +0000
> Chris Packham <Chris.Packham@xxxxxxxxxxxxxxxxxxx> wrote:
>
>> Hi All,
>>
>> On 8/02/19 12:58 PM, Przemyslaw Sobon wrote:
>>> Fixes: dfeae1073583(mtd: cfi_cmdset_0002: Change write buffer to
>>>          check correct value)
>>>
>>> There was an endless loop in CFI Flash driver when a value was written
>>> incorrectly. In such case chip_ready returns true but chip_good returns
>>> false and we never get out of the loop.
>>>
>>> The solution was to break the loop in 2 cases, either device is ready or
>>> device is not ready and timeout elapsed. The correctness of the write is
>>> checked after the loop ended. That way we ensure the loop always ends.
>>>
>>> Signed-off-by: Przemyslaw Sobon <psobon@xxxxxxxxxx>
>> Mark (cc'd) has done some testing here, and assuming he's happy with the
>> forgery.
>>
>> Tested-by: Mark Tomlinson <Mark.Tomlinson@xxxxxxxxxxxxxxxxxxx>
> I'm a bit lost. Ikegami told us that checking for chip_ready() was not
> enough and chip_good() could return true after a few tests even though
> it initially returned false.
>
> I'd really like to get that fixed, but it looks like you haven't reached
> a consensus on what the appropriate fix is :-/.
I have done some further testing and this patch doesn't work 100%. It
appears at least some flash chips do not start toggling immediately, and
therefore chip_ready() can return true early. A timeout is reported,
even though that isn't what happened.

chip_good() makes an additional check over chip_ready() and is the call
I believe we should be using. I will submit a new patch which should fix
the infinite loop as well as not mis-reporting errors.

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