[v2 5/9] clocksource: tegra: Enable ARM arch_timer with TSC

[Hiroshi Doyu]

Stephen Warren <swarren at wwwdotorg.org> wrote @ Tue, 8 Jan 2013 23:41:42 +0100:

> On 01/08/2013 09:07 AM, Marc Zyngier wrote:
> > On 08/01/13 12:47, Hiroshi Doyu wrote:
> >> Add platform enabler for ARM arch_timer(TSC). TSC is more fine grained
> >> timer than TMR0. If it's available, it will be used for clock source
> >> and sched_clock. Otherwise, TMR0 is used. In any case TMR0 is
> >> necessary for clock event.
> 
> >> diff --git a/drivers/clocksource/tegra20_timer.c b/drivers/clocksource/tegra20_timer.c
> 
> >> +/* FIXME: only secure mode is supported. */
> > 
> > And this is a bug, as far as I'm concerned.
> > 
> >> +static int tegra_arch_timer_init(void)
> 
> >> +	clk = clk_get_sys("clk_m", NULL);
> >> +	if (IS_ERR(clk)) {
> >> +		freq = 12000000;
> >> +		pr_warn("Unable to get timer clock. Assuming 12Mhz input clock.\n");
> >> +	} else {
> >> +		freq = clk_get_rate(clk);
> >> +		clk_put(clk);
> >> +	}
> >> +	writel_relaxed(freq, tsc_base + TSC_CNTFID0);
> >> +
> >> +	/* CNTFRQ */
> >> +	asm("mcr p15, 0, %0, c14, c0, 0\n" : : "r" (freq));
> >> +	asm("mrc p15, 0, %0, c14, c0, 0\n" : "=r" (val));
> >> +	BUG_ON(val != freq);
> > 
> > No, not again! Like I said last year, this won't fly. So instead of
> > trying to work around a broken firmware, let's do the right thing.
> 
> OK, so I understand you want to firmware/bootloader/... to write the
> value into that register instead, so this all works in non-secure mode
> (which sounds like a fine objection), but ...

If possible, I want to run kernel without bootloader initializing TSC
. IOW, I want to allow legacy bootloaders to boot kernel with ARM arch
timer.