mtd: cfi_cmdset_0002: Read data 3 times to check write operation status

[Joakim Tjernlund]

On Tue, 2018-04-24 at 05:54 +0000, IKEGAMI Tokunori wrote:
> 
> Hi,
> 
> Let us consult to change mtd cfi_cmdset_0002 to read data 3 times as below patch.
> Can we change the mtd cfi_cmdset_0002 driver like this?
> If any comment or concern please let us know.
> 
> From d924822c996b9c0eccc815e5018a0c3ea6077137 Mon Sep 17 00:00:00 2001
> From: Tokunori Ikegami <ikegami at allied-telesis.co.jp>
> Date: Tue, 24 Apr 2018 13:26:37 +0900
> Subject: [PATCH 2/2] mtd: cfi_cmdset_0002: Read data 3 times to check write
>  operation status
> 
> Cypress S29GLxxxP flash is needed to read data 3 times to check DQ6 toggles.
> Actually the read data is sometimes changed by the 3rd reading.
> Also this is caused on other flash device also.
> The flash write failure is possible to be caused by the error.
> To resolve the issue change the read number of times to 3 from 2.

Hi 

I find this a bit odd. I am looking at some other erase suspend problems we
see on Cypress AMD NOR flash and I have noted that there is more than just DQ6 toggling.
Checking DQ5 in combination with DQ6 is one.
How did you you arrive at reading 3 times is correct? Is the any documentation
supporting this?

All in all, error handling in cmdset0002 is lacking.

 Jocke