Hi Mark,
On 18 March 2017 at 03:05, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> On Tue, Feb 07, 2017 at 02:50:06AM +0800, fu.wei@xxxxxxxxxx wrote:
>> From: Fu Wei <fu.wei@xxxxxxxxxx>
>>
>> Currently, arch_timer_rate is used to store the frequency got from per-cpu
>> arch-timer or the memory-mapped (MMIO) timers. But those values come from
>> different registers which should all be initialized by firmware.
>>
>> This patch remove arch_timer_rate, and use arch_timer_sysreg_freq and
>> arch_timer_mmio_freq instead.
>>
>> Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
>
> Thanks for attacking this. Generally, I do think this is the right thing
> to do.
>
> However...
>
>> @@ -1070,10 +1077,9 @@ static int __init arch_timer_mem_init(struct device_node *np)
>> * Try to determine the frequency from the device tree,
>> * if fail, get the frequency from the CNTFRQ reg of MMIO timer.
>> */
>> - if (!arch_timer_rate &&
>> - of_property_read_u32(np, "clock-frequency", &arch_timer_rate))
>> - arch_timer_rate = arch_timer_get_mmio_freq(base);
>> - if (!arch_timer_rate) {
>> + if (of_property_read_u32(np, "clock-frequency", &arch_timer_mmio_freq))
>> + arch_timer_mmio_freq = arch_timer_get_mmio_freq(base);
>> + if (!arch_timer_mmio_freq) {
>> pr_err(FW_BUG "frequency not available for MMIO timer.\n");
>> ret = -EINVAL;
>> goto out;
>
> ... unfortunately, I believe that this will break some DT platforms that
> have been (unintentionally) relying on the way currently allow the
> frequency to be probed from either the MMIO timer or the sysreg timer.
>
Ah, I 'm really not aware of this. Thanks for pointing it out.
> So while the above was my suggestion, it was not my best.
>
> For the timebeing, let's leave the single arch_timer_rate, but ensure
> that it doesn't get in the way fo the ACPI code, by making the ACPI
> probe path:
>
> * Probe the sysreg timers first, using the sysreg cntfrq().
>
> * Probe the MMIO timers second, verifying that each MMIO cntfrq matches
> the already-probed sysreg cntfrq.
>
> ... which is what I believe you suggested previously.
OK, NP, will do this way.
>
> Thanks,
> Mark.
--
Best regards,
Fu Wei
Software Engineer
Red Hat
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