Re: [PATCH] mtd: rawnand: fsmc: Keep bank enable bit set

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Linus,

Please don't forget to Cc: me when it comes to NAND-related changes :)

Boris Brezillon <bbrezillon@kernel.org> wrote on Wed, 9 Jan 2019
23:12:59 +0100:

> On Wed,  9 Jan 2019 22:51:44 +0100
> Linus Walleij <linus.walleij@linaro.org> wrote:
> 
> > Hammering the "bank enable" (PBKEN) bit on and off between
> > every command crashes the Nomadik NHK15 with this message:
> > 
> > Scanning device for bad blocks
> > Unhandled fault: external abort on non-linefetch (0x008) at 0xcc95e000
> > pgd = (ptrval)
> > [cc95e000] *pgd=0b808811, *pte=40000653, *ppte=40000552
> > Internal error: : 8 [#1] PREEMPT ARM
> > Modules linked in:
> > CPU: 0 PID: 1 Comm: swapper Not tainted 4.20.0-rc2+ #72
> > Hardware name: Nomadik STn8815
> > PC is at fsmc_exec_op+0x194/0x204
> > (...)
> > 
> > After a discussion we (me and Boris Brezillion) start to suspect  
> 
> 				      ^ Brezillon :-)
> 
> > that this bit does not immediately control the chip select line
> > at all, it rather enables access to the bank and the hardware
> > will drive the CS autonomously. If there is a NAND chip connected,
> > we should keep this enabled.
> > 
> > As fsmc_nand_setup() sets this bit, we can simply remove the
> > offending code.
> > 
> > Fixes: 550b9fc4e3af ("mtd: rawnand: fsmc: Stop implementing ->select_chip()")
> > Signed-off-by: Linus Walleij <linus.walleij@linaro.org>  
> 
> Reviewed-by: Boris Brezillon <bbrezillon@kernel.org>
> 
> Would be great if someone could validate our assumption with a scope.
> This being said, given the description of the FSMC logic, I have little
> doubt that this bit does not directly controls the CE line, otherwise
> concurrent accesses to different memories on the same bus wouldn't work
> or would require a lot more synchronization than we currently have in
> Linux.
> 

Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>


Thanks,
Miquèl