Re: [PATCH] mtd: rawnand: fsmc: Make sure we wait tWB before polling the STATUS reg

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Fri, 4 May 2018 11:45:10 +0200
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> Hi Boris,
> 
> On Thu,  3 May 2018 09:45:44 +0200, Boris Brezillon
> <boris.brezillon@bootlin.com> wrote:
> 
> > NAND chips require a bit of time to take the NAND operation into account
> > and set the BUSY bit in the STATUS reg. Make sure we don't poll the
> > STATUS reg too early.
> > 
> > Fixes: 4da712e70294 ("mtd: nand: fsmc: use ->exec_op()")
> > Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> > ---
> >  drivers/mtd/nand/raw/fsmc_nand.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/mtd/nand/raw/fsmc_nand.c b/drivers/mtd/nand/raw/fsmc_nand.c
> > index 28c48dcc514e..0960665858b7 100644
> > --- a/drivers/mtd/nand/raw/fsmc_nand.c
> > +++ b/drivers/mtd/nand/raw/fsmc_nand.c
> > @@ -18,6 +18,7 @@
> >  
> >  #include <linux/clk.h>
> >  #include <linux/completion.h>
> > +#include <linux/delay.h>
> >  #include <linux/dmaengine.h>
> >  #include <linux/dma-direction.h>
> >  #include <linux/dma-mapping.h>
> > @@ -695,6 +696,13 @@ static int fsmc_exec_op(struct nand_chip *chip, const struct nand_operation *op,
> >  			pr_debug("  ->WAITRDY  [max %d ms]\n",
> >  				 instr->ctx.waitrdy.timeout_ms);
> >  
> > +			/*
> > +			 * Make sure we wait tWB before polling the STATUS
> > +			 * register.
> > +			 */
> > +			if (op_id && op->instrs[op_id - 1].delay_ns)
> > +				ndelay(op->instrs[op_id - 1].delay_ns);
> > +
> >  			ret = nand_soft_waitrdy(chip,
> >  						instr->ctx.waitrdy.timeout_ms);
> >  			break;  
> 
> I'm afraid that we encounter this exact same issue with all the drivers
> using nand_soft_waitrdy() whenever the controller does not already
> wait for tWB. Could we force a tWB_max delay directly inside
> nand_soft_waitrdy()?

Yep, I agree. I'll send a new version doing that.

Thanks,

Boris