Messages in this thread | | | Date | Wed, 25 Nov 2009 23:07:48 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] spi: SuperH MSIOF SPI Master driver |
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On Thu, 26 Nov 2009 15:43:16 +0900 Paul Mundt <lethal@linux-sh.org> wrote:
> > > +static void sh_msiof_modify_ctr_wait(struct sh_msiof_spi_priv *p, > > > + unsigned long clr, unsigned long set) > > > +{ > > > + unsigned long mask = clr | set; > > > + unsigned long data; > > > + > > > + data = sh_msiof_read(p, CTR); > > > + data &= ~clr; > > > + data |= set; > > > + sh_msiof_write(p, CTR, data); > > > + > > > + while ((sh_msiof_read(p, CTR) & mask) != set) > > > + ; > > > > hm, confidence. No timeout needed here? > > > This definitely needs a timeout, nothing involving SPI inspires > confidence. A cpu_relax() to prevent the compiler from optimizing the > loop out would help, too.
We generally don't bother with the relax in an IO polling loop like this. It involves an IO read/write which the compiler cannot fiddle with and I believe that CPUs will generally take the opportunity to have a little snooze while the slow IO operation is happening.
Can't hurt though ;)
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