Messages in this thread | | | From | Matthijs van Duin <> | Date | Sat, 30 May 2015 17:22:11 +0200 | Subject | Re: runtime check for omap-aes bus access permission (was: Re: 3.13-rc3 (commit 7ce93f3) breaks Nokia N900 DT boot) |
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On 29 May 2015 at 17:50, Tony Lindgren <tony@atomide.com> wrote: > I believe some TI kernels use strongly-ordered mappings, mainline > kernel does not. Which kernel version are you using?
Normally I periodically rebuild based on Robert C Nelson's -bone kernel (but with heavily customized config). I also tried a plain 4.1.0-rc5-bone3, the generic 4.1.0-rc5-armv7-x0 (the most vanilla-looking kernel I could find in my debian package list), and for the heck of it also the classic 3.14.43-ti-r66.
In all cases I observed a synchronous bus error (dubiously reported as "external abort on non-linefetch (0x1818)") on an AM335x with this trivial test:
int main() { int fd = open( "/dev/mem", O_RDWR | O_DSYNC ); if( fd < 0 ) return 1; void *ptr = mmap( NULL, 4096, PROT_WRITE, MAP_SHARED, fd, 0x42000000 ); if( ptr == MAP_FAILED ) return 1; *(volatile int *)ptr = 0; return 0; }
I even considered for a moment that maybe the AM335x has some "all writes non-posted" thing enabled (which I think is available as a switch on OMAP 4/5?). It seemed unlikely, but since most of my exploration of interconnect behaviour was done on a DM814x, I double-checked by performing the same write in a baremetal test program (with that region configured Device-type in the MMU). As expected, no data abort occurred, so writes most certainly are posted.
So I have trouble coming up with any explanation for this other than the use of strongly-ordered mappings.
(Curiously BTW, omitting O_DSYNC made no difference.)
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