[Adding Stefano] On Thu, Mar 8, 2018 at 1:21 AM, Yasushi SHOJI <yasushi.sh...@gmail.com> wrote: > Without the volatile attribute, compilers are entitled to optimize out > the same asm(). In the case of __udelay() in syscounter.c, it calls > `get_ticks()` twice, one for the starting time and the second in the > loop to check the current time. When compilers inline `get_ticks()` > they see the same `mrrc` instructions and optimize out the second one. > This leads to infinite loop since we don't get updated value from the > system counter. > > Here is a portion of the disassembly of __udelay: > > 88: 428b cmp r3, r1 > 8a: f8ce 20a4 str.w r2, [lr, #164] ; 0xa4 > 8e: bf08 it eq > 90: 4282 cmpeq r2, r0 > 92: f8ce 30a0 str.w r3, [lr, #160] ; 0xa0 > 96: d3f7 bcc.n 88 <__udelay+0x88> > 98: e8bd 8cf0 ldmia.w sp!, {r4, r5, r6, r7, sl, fp, pc} > > Note that final jump / loop at 96 to 88, we don't have any `mrrc`. > > With a volatile attribute, the above changes to this: > > 8a: ec53 2f0e mrrc 15, 0, r2, r3, cr14 > 8e: 42ab cmp r3, r5 > 90: f8c1 20a4 str.w r2, [r1, #164] ; 0xa4 > 94: bf08 it eq > 96: 42a2 cmpeq r2, r4 > 98: f8c1 30a0 str.w r3, [r1, #160] ; 0xa0 > 9c: d3f5 bcc.n 8a <__udelay+0x8a> > 9e: e8bd 8cf0 ldmia.w sp!, {r4, r5, r6, r7, sl, fp, pc} > a2: bf00 nop > > I'm advised[1] to put volatile on all asm(), so this commit also adds it > to the asm() in timer_init(). > > [1]: https://lists.denx.de/pipermail/u-boot/2018-March/322062.html > > Signed-off-by: Yasushi SHOJI <yasushi.sh...@gmail.com> > Reviewed-by: Fabio Estevam <fabio.este...@nxp.com>
Hi Stefano, Do you think this one could be applied for the upcoming release? Thanks > --- > arch/arm/mach-imx/syscounter.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/mach-imx/syscounter.c b/arch/arm/mach-imx/syscounter.c > index 9290918dca..1d4ebfe343 100644 > --- a/arch/arm/mach-imx/syscounter.c > +++ b/arch/arm/mach-imx/syscounter.c > @@ -62,7 +62,7 @@ int timer_init(void) > unsigned long val, freq; > > freq = CONFIG_SC_TIMER_CLK; > - asm("mcr p15, 0, %0, c14, c0, 0" : : "r" (freq)); > + asm volatile("mcr p15, 0, %0, c14, c0, 0" : : "r" (freq)); > > writel(freq, &sctr->cntfid0); > > @@ -82,7 +82,7 @@ unsigned long long get_ticks(void) > { > unsigned long long now; > > - asm("mrrc p15, 0, %Q0, %R0, c14" : "=r" (now)); > + asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (now)); > > gd->arch.tbl = (unsigned long)(now & 0xffffffff); > gd->arch.tbu = (unsigned long)(now >> 32); > -- > 2.16.2 > _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot