Strange arch/mips/delay.c

Strange arch/mips/delay.c

[Loïc Grenié]

  I could not compile for mips without something similar to the
following patch. As far as I can say __udelay and __ndelay
are costly nops (with __ndelay not compiling at all) without
the patch.

  At that point, it might be interesting to change
the 0x00000005uLL by 0x00000045uLL and the >> 32
by >> 36 (the precision is much better and the cost
should be the same -- obviously there is a slightly higher
risk of overlow).

    Thanks,

           Loïc Grenié

Signed-off-by: Loic Grenie <loic.grenie@gmail.com>

--- a/arch/mips/lib/delay.c
+++ b/arch/mips/lib/delay.c
@@ -43,7 +43,7 @@ void __udelay(unsigned long us)
 {
        unsigned int lpj = current_cpu_data.udelay_val;

-       __delay((us * 0x000010c7 * HZ * lpj) >> 32);
+       __delay((us * 0x000010c7uLL * HZ * lpj) >> 32);
 }
 EXPORT_SYMBOL(__udelay);

@@ -51,6 +51,6 @@ void __ndelay(unsigned long ns)
 {
        unsigned int lpj = current_cpu_data.udelay_val;

-       __delay((us * 0x00000005 * HZ * lpj) >> 32);
+       __delay((ns * 0x00000005uLL * HZ * lpj) >> 32);
 }
 EXPORT_SYMBOL(__ndelay);

Re: Strange arch/mips/delay.c

[Ralf Baechle]

On Sat, Aug 01, 2009 at 07:37:18PM +0200, Loïc Grenié wrote:

>   I could not compile for mips without something similar to the
> following patch. As far as I can say __udelay and __ndelay
> are costly nops (with __ndelay not compiling at all) without
> the patch.
> 
>   At that point, it might be interesting to change
> the 0x00000005uLL by 0x00000045uLL and the >> 32
> by >> 36 (the precision is much better and the cost
> should be the same -- obviously there is a slightly higher
> risk of overlow).

Later versions of the kernel already contain a similar fix.  I've not
propagated MIPS fixes into upstream -stable but the fixes are available
in the -stable branches of the MIPS git repository at
git://git.linux-mips.org/pub/scm/linux.git, the tarballs created from
that repository available for download on {ftp,www}.linux-mips.org  or
on git.kernel.org.

  Ralf