Subject: [PATCH v2 12/27] mtd: nand: pxa3xx: Use a completion to signal device ready

From: [email-masked] (Ezequiel Garcia)
Date: Mon, 4 Nov 2013 10:51:12 -0300

On Sun, Nov 03, 2013 at 06:03:39PM -0500, Huang Shijie wrote:
> On Fri, Oct 18, 2013 at 08:02:39PM -0300, Ezequiel Garcia wrote:
> > Apparently, the expected behavior of the waitfunc() NAND chip call
> > is to wait for the device to be READY (this is a standard chip line).
> > However, the current implementation does almost nothing, which opens
> > a possibility to issue a command to a non-ready device.
> > 
> > Fix this by adding a new completion to wait for the ready event to arrive.
> > 
> > Because the "is ready" flag is cleared from the controller status
> > register, it's needed to store that state in the driver, and because the
> > field is accesed from an interruption, the field needs to be of an
> > atomic type.
> > 
> > Signed-off-by: Ezequiel Garcia <[email-masked]>
> > ---
> >  drivers/mtd/nand/pxa3xx_nand.c | 45 +++++++++++++++++++++++++++++-------------
> >  1 file changed, 31 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/mtd/nand/pxa3xx_nand.c b/drivers/mtd/nand/pxa3xx_nand.c
> > index 95e2ce3..1ceccb6 100644
> > --- a/drivers/mtd/nand/pxa3xx_nand.c
> > +++ b/drivers/mtd/nand/pxa3xx_nand.c
> > @@ -35,6 +35,7 @@
> >  
> >  #include <linux/platform_data/mtd-nand-pxa3xx.h>
> >  
> > +#define NAND_DEV_READY_TIMEOUT  50
> >  #define	CHIP_DELAY_TIMEOUT	(2 * HZ/10)
> >  #define NAND_STOP_DELAY		(2 * HZ/50)
> >  #define PAGE_CHUNK_SIZE		(2048)
> > @@ -166,7 +167,7 @@ struct pxa3xx_nand_info {
> >  	struct clk		*clk;
> >  	void __iomem		*mmio_base;
> >  	unsigned long		mmio_phys;
> > -	struct completion	cmd_complete;
> > +	struct completion	cmd_complete, dev_ready;
> >  
> >  	unsigned int 		buf_start;
> >  	unsigned int		buf_count;
> > @@ -196,7 +197,13 @@ struct pxa3xx_nand_info {
> >  	int			use_ecc;	/* use HW ECC ? */
> >  	int			use_dma;	/* use DMA ? */
> >  	int			use_spare;	/* use spare ? */
> > -	int			is_ready;
> > +
> > +	/*
> > +	 * The is_ready flag is accesed from several places,
> > +	 * including an interruption hander. We need an atomic
> > +	 * type to avoid races.
> > +	 */
> > +	atomic_t		is_ready;
> Do we really need to change it to atomic_t?
> 
> IMHO, the write is also a atomic operation.
> 

I see. Well, if reading and setting an int type is atomic
(at least on ARM), then of course we don't need the atomic_t.

On the other side, it really shouldn't hurt too much and
it emphasize the fact that it's accesed from the IRQ handler
and the other callbacks (such as waitfunc).

So, I'm still inclined to keeping it atomic.

Does it sound stupid?
-- 
Ezequiel Garc?a, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com