DQ5 & DQ6 in chips/cfi_cmdset_0002.c (Dairy Queen 5 warning)

[Steve Wahl]

Thayne, 

I have a patch that I was given permission to check in, but never got
around to it, that covers a similar "DQ5 raised" problem.

I would wager you are running into the same problem I did, and that
your chips compatibly support DQ5, if not as a watchdog, at least by
holding it low while programming.

Can you look at my previous posts on this, try my patch (if you don't
have interleaved chips -- contact me if you do), and see if it works
for you?

http://lists.infradead.org/pipermail/linux-mtd/2003-January/006780.html

--> Steve


On Tue, Mar 11, 2003 at 05:25:15PM -0700, Thayne Harbaugh wrote:
> For some reason I am confused: I get the feeling that what I'm trying to
> understand is obvious - I just can't see the forest for the trees.  Will
> someone help me understand?
> 
> cfi_cmdset_0002.c has several functions that use dq5 and dq6 for
> monitoring the status of erase and write operations:
> 
> dq6 = CMD(1<<6);
> dq5 = CMD(1<<5);
> 
> Apparently, from the code dq6 toggles during erase/read operations and
> dq5 is low until the erase/read operation times out and then goes high
> (somewhat like a watchdog bit).
> 
> My understanding, at least for the SST 49LF040 and PMC Pm49L004 is that
> dq6 toggles during erase/write and dq7 is inverted until the erase/write
> operation completes.  This causes me to expect to see the following code
> rather than what is written above (not to mention that most everything
> in do_write_one_word() should be adapted for dq7 invert):
> 
> dq7 = CMD(1<<7); /* invert */
> dq6 = CMD(1<<6); /* toggle */
> 
> The differences give me the feeling that there really are two different
> classes of cfi_cmdset_0002 - those devices that have a dq5 watchdog and
> those devices that don't have the watchdog, but have a bit inverter on
> dq7.
> 
> Am I not understanding what happens on bits 0-5 during an erase/write
> operation?  The PMC and SST chips don't mention a thing about dq5
> behavior.  If they don't have the dq5 watchdog timer then they will
> behave in an undefined way (depending on the state of bit 5 in the
> written word) with the current dq5 checking.  This explains the many
> warnings I see with the SST and PMC chips in do_write_oneword(),
> 
> "Warning: DQ5 raised while program operation was in progress, however
> operation completed OK"
> 
> Around here we refer to this as the "Dairy Queen 5" warning.
> 
> Obviosly, during an erase that completes prior to dq5 being read-back,
> dq5 will be high and the current algorithm is erroneously correct.  This
> can explain why I have not seen the same message in do_erase_oneblock().
> 
> Furthermore, the SST documentation on page 10 refers to "spurios
> rejection" of good writes - differentiating between a write that
> succeeds that appears to fail and a write that fails.  It says that a
> write that appears to fail needs to be read back two more times
> successfully to filter out spurious rejection.
> 
> Comments?  What should change to improve the operation completion
> check?  Should cfi_cmdset_0002 be adapted to handle multiple types of
> polling or should another command set be written?
> 
> -- 
> Thayne Harbaugh
> Linux Networx