[PATCH 0/2] mtd: nand: raw: atmel: R/B gpio on sam9x60

[Eugen Hristev]

Added Mihai who tested this a lot at some point in time

Eugen

On 8/8/23 16:02, Alexander Dahl wrote:
> Hello everyone,
> 
> this is a patch series wtih some real fixes _and_ a question or some
> kind of support request in the cover letter.  I would be happy if anyone
> could read the cover letter carefully and answer to that one what might
> be the problem I see. O:-)
> 
> I'm currently working on the sam9x60-curiosity board and especially
> trying to get it booting from onboard raw NAND flash.  As reported in my
> last series I got the flash recognized already.  However interacting
> with it was terribly slow, because nand_wait_ready() calling
> atmel_nand_dev_ready() ran into a 400ms timeout in several occasions,
> especially when reading from the device.  Reading a single block
> triggered that timeout two times per page, which summed up to over 50
> seconds for 64 × 4096 = 256k Bytes!
> 
> (You can have U-Boot print that warning from nand_wait_ready() by
> increasing the console log level to at least "warn".)
> 
> Note: the dts from atmel/next seems correct to me, I double checked that
> again.  My own debug log messages showed the GPIO is accessed, and if
> you add enough debug messages sometimes the timeout is not reached, so
> I'm sure the NAND chip eventually switches that R/B line and the code
> correctly sees that, that line level change however takes ages,
> something between 400ms and 500ms most of the times.
> 
> I vaguely remembered on SAMA5D2 the old atmel raw nand driver is used
> which does not support reading the R/B signal, but nevertheless works.
> I'm not familiar in detail with those raw NAND flash chips, but as far
> as I can understand, there are other ways to determine if the chip is
> ready or busy.  So after I removed that rb-gpio parameter from
> 'at91-sam9x60_curiosity.dts' I ran into the bug fixed by patch 2.
> 
> With that patch applied _and_ rb-gpio still removed from dts, raw NAND
> access is reasonably fast on sam9x60-curiosity board.  (You might want
> to rebase to atmel/next for testing this.)  Not sure if I should send a
> patch for that dts change, because I suppose it's a workaround only and
> not addressing the actual cause?
> 
> I think the fix is correct in itself, I tested different combinations
> and compared with the driver in Linux, however …
> 
> Can anyone explain to me, why flash access is sooo slow if the R/B gpio
> is used?  Especially in comparision to Linux, where I don't need to
> remove that thing from dts and it works reasonably fast?
> 
> The actual flash chip is a Macronix MX30LF4G28AD, 512 MiB, SLC, erase
> size: 256 KiB, page size: 4096, OOB size: 256.
> 
> Greets
> Alex
> 
> P.S.: although not returned by get_maintainer.pl I added Eugen to Cc
> because he is maintainer of the at91 and might have some insight if it
> is a general problem of the nand controller in at91 socs?
> 
> Alexander Dahl (2):
>    mtd: nand: raw: atmel: Remove duplicate line
>    mtd: nand: raw: atmel: Add error handling when rb-gpios missing
> 
>   drivers/mtd/nand/raw/atmel/nand-controller.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
> 
> 
> base-commit: a169438411f9277cc689c14078151aa1d1caae3c