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Date: Sun, 19 Jun 2016 14:57:35 +0200
From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Hauke Mehrtens <hauke@hauke-m.de>
Cc: richard@nod.at, dwmw2@infradead.org, computersforpeace@gmail.com,
 linux-mtd@lists.infradead.org, john@phrozen.org
Subject: Re: [PATCH v2 4/8] MTD: xway: remove endless loop
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On Sun, 19 Jun 2016 14:32:56 +0200
Hauke Mehrtens <hauke@hauke-m.de> wrote:

> On 06/19/2016 02:14 PM, Boris Brezillon wrote:
> > On Sat, 18 Jun 2016 21:14:08 +0200
> > Hauke Mehrtens <hauke@hauke-m.de> wrote:
> >   
> >> From: John Crispin <john@phrozen.org>
> >>
> >> The reset loop logic could run into a endless loop. Lets fix it as
> >> requested.
> >> http://lists.infradead.org/pipermail/linux-mtd/2012-September/044240.html
> >>
> >> Signed-off-by: John Crispin <john@phrozen.org>
> >> Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
> >> ---
> >>  drivers/mtd/nand/xway_nand.c | 10 ++++++++--
> >>  1 file changed, 8 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/mtd/nand/xway_nand.c b/drivers/mtd/nand/xway_nand.c
> >> index 346781a..61176c4 100644
> >> --- a/drivers/mtd/nand/xway_nand.c
> >> +++ b/drivers/mtd/nand/xway_nand.c
> >> @@ -73,16 +73,22 @@ struct xway_nand_data {
> >>  static void xway_reset_chip(struct nand_chip *chip)
> >>  {
> >>  	unsigned long nandaddr = (unsigned long) chip->IO_ADDR_W;
> >> +	unsigned long timeout;
> >>  	unsigned long flags;
> >>  
> >>  	nandaddr &= ~NAND_WRITE_ADDR;
> >>  	nandaddr |= NAND_WRITE_CMD;
> >>  
> >>  	/* finish with a reset */
> >> +	timeout = jiffies + msecs_to_jiffies(20);
> >> +
> >>  	spin_lock_irqsave(&ebu_lock, flags);
> >>  	writeb(NAND_WRITE_CMD_RESET, (void __iomem *) nandaddr);
> >> -	while ((ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_WR_C) == 0)
> >> -		;
> >> +	do {
> >> +		if ((ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_WR_C) == 0)
> >> +			break;
> >> +		cond_resched();
> >> +	} while (!time_after_eq(jiffies, timeout));
> >>  	spin_unlock_irqrestore(&ebu_lock, flags);
> >>  }
> >>    
> > 
> > AFAICS, this function is doing exactly what  
> > ->cmdfunc(NAND_CMD_RESET, -1 , -1) does, except for the NAND_WAIT_WR_C  
> > test? What is this bit representing?
> > 
> > I'd really prefer if you kill this function and just call ->cmdfunc()
> > instead.
> >   
> 
> NAND_WAIT_WR_C indicates that the previous operation is finished.

Does "previous operation done" implies "NAND device is ready" (R/B pin
set to ready state and NAND_CMD_STATUS return ready)?
If that's not the case, then I'm not sure it's safe to reset the NAND
without waiting for the device to be ready, so I'd recommend using
->cmdfunc(RESET) in that case.