Re: [PATCH] PNX8550 NAND flash driver

Thomas Gleixner
2006-07-26T06:59:12Z

On Tue, 2006-07-25 at 20:34 +0200, Jurgen wrote:
> Root cause of the problem lies within the early implementation of the
> low-level NAND commands. There was a severe risk that the PCI accesses
> were stalled because of a Read Status command for the NAND Flash. This
> Read Status was launched immediately after program/erase command. The
> hardware itself will wait for the Ready/Busy to be high and only then
> launch the Read Status command. This behavior caused timeout on the
> internal bus because PCI was unable to use the pins during this wait.

The hardware design is broken. Status Read can be requested while R/B is
low. See NAND datasheets.

> If this problem was coinciding with an ISR that tried to perform a PCI
> status register, then this PCI access could possibly timeout (because
> the PCI pins were already claimed for the XIO access that is depending
> on the RBY signal).
>
> Since the problem only showed during the PCI device ISR, the
> quick'n'dirty hack was to disable interrupts during XIO accesses.
>
> A better fix that should be available somewhere, is to improve the
> low-level NAND driver that will first check the status of the Ready/Busy
> line and only THEN launch the Read NAND Status command...

Thats not an improvement. Thats a hack for your broken hardware. You'd
burden the R/B check on every sane hardware out there.

You can add the R/B check to the chip->cmd_ctrl() function of your board
driver.

tglx