linux-kernel - Re: [PATCH v3 1/2] mtd: nand: pxa3xx: Fix PIO FIFO draining

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Message-ID: <20150216205825.GG25269@lukather>
Date:	Mon, 16 Feb 2015 21:58:25 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:	Gregory Clement <gregory.clement@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Brian Norris <computersforpeace@...il.com>,
	Lior Amsalem <alior@...vell.com>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Thomas Petazzoni <thomas@...e-electrons.com>,
	Seif Mazareeb <seif@...vell.com>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	Sudhakar Gundubogula <sudhakar@...vell.com>,
	Nadav Haklai <nadavh@...vell.com>,
	Boris Brezillon <boris@...e-electrons.com>,
	linux-mtd@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/2] mtd: nand: pxa3xx: Fix PIO FIFO draining

Hi Robert,

On Mon, Feb 16, 2015 at 09:11:24PM +0100, Robert Jarzmik wrote:
> Maxime Ripard <maxime.ripard@...e-electrons.com> writes:
> 
> >  drivers/mtd/nand/pxa3xx_nand.c | 47 ++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 41 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/mtd/nand/pxa3xx_nand.c b/drivers/mtd/nand/pxa3xx_nand.c
> > index 96b0b1d27df1..b2d8d6960765 100644
> > --- a/drivers/mtd/nand/pxa3xx_nand.c
> > +++ b/drivers/mtd/nand/pxa3xx_nand.c
> > @@ -480,6 +480,41 @@ static void disable_int(struct pxa3xx_nand_info *info, uint32_t int_mask)
> >  	nand_writel(info, NDCR, ndcr | int_mask);
> >  }
> >  
> > +static void drain_fifo(struct pxa3xx_nand_info *info, void *data, int len)
> > +{
> > +	if (info->ecc_bch) {
> > +		int index = 0;
> > +
> > +		while (index < (len * 4)) {
> > +			u32 timeout;
> > +
> > +			__raw_readsl(info->mmio_base + NDDB, data + index, 8);
> > +
> > +			/*
> > +			 * According to the datasheet, when reading
> > +			 * from NDDB with BCH enabled, after each 32
> > +			 * bytes reads, we have to make sure that the
> > +			 * NDSR.RDDREQ bit is set
> > +			 */
> > +			for (timeout = 0;
> > +			     !(nand_readl(info, NDSR) & NDSR_RDDREQ);
> > +			     timeout++) {
> > +				if (timeout >= 5) {
> > +					dev_err(&info->pdev->dev,
> > +						"Timeout on RDDREQ while draining the FIFO\n");
> > +					return;
> > +				}
> > +
> > +				mdelay(1);
> So in worst case, we'll end up with 4 times mdelay(1) times len / 32.
> For a 2048 page, it is : 256ms where everything is stuck (mdelay and not
> msleep).
> 
> I know you had no choice because this is called from interrupt handler (top
> half). But having a irq handler and a irq thread handler would solve that issue,
> and you'll end up with msleep(1) in this code.
> 
> I don't think an mdelay(256) is acceptable.

That's very true that this driver would need some love, but
valentine's day was last week.

I'm sorry, but this is a patch targeted for stable. This is a pure
bugfix. I won't rewrite the whole driver solely to make the driver
better, especially since that would make such a patch (or more likely
a whole serie) unsuitable for stable.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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