Messages in this thread | | | Subject | Re: [PATCH] MTD: LPC32xx SLC NAND driver | From | Artem Bityutskiy <> | Date | Tue, 15 May 2012 10:55:43 +0300 |
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I am CCing few other guys who take care of several drivers which use similar way of busy-waiting - probably you could change it?
Bastian: drivers/mtd/nand/sh_flctl.c Lars-Peter: drivers/mtd/nand/jz4740_nand.c Huang: drivers/mtd/nand/gpmi-nand/gpmi-lib.c Lei Wen: drivers/mtd/nand/pxa3xx_nand.c
On Sat, 2012-05-12 at 15:29 +0200, Roland Stigge wrote: > + /* > + * The DMA is finished, but the NAND controller may still have > + * buffered data. Wait until all the data is sent. > + */ > + timeout = LPC32XX_DMA_SIMPLE_TIMEOUT; > + while ((readl(SLC_STAT(host->io_base)) & SLCSTAT_DMA_FIFO) > + && (timeout > 0)) > + timeout--; > + if (!timeout) { > + dev_err(mtd->dev.parent, "FIFO held data too long\n"); > + status = -EIO; > + }
I know the MTD tree is full of this, but this is bad, I think. The timeout should be time-backed, not CPU-cycles-backed.
I do not know the best way to do this, hopefully someone in the arm list could suggest, but the following pattern is at least better:
/* Chip reaction time timeout in milliseconds */ #define LPC32XX_DMA_TIMEOUT 100
timeout = loops_per_jiffy * msecs_to_jiffies(LPC32XX_DMA_TIMEOUT);
while ((readl(...)) && timeout-- > 0) cpu_relax();
if (!timeout) error;
So basically I turned your hard-coded iterations count into a time-based timeout. I also used cpu_relax() which is commonly used in tight-loops like this. Here is a piece of documentation about cpu_relax():
" The right way to perform a busy wait is:
while (my_variable != what_i_want) cpu_relax();
The cpu_relax() call can lower CPU power consumption or yield to a hyperthreaded twin processor; it also happens to serve as a compiler barrier, so, once again, volatile is unnecessary. Of course, busy- waiting is generally an anti-social act to begin with. "
-- Best Regards, Artem Bityutskiy [unhandled content-type:application/pgp-signature] | |