On Fri, Jan 19, 2018 at 5:34 PM, Greentime Hu <green.hu@xxxxxxxxx> wrote:
> Hi, Arnd:
>
> 2018-01-18 18:11 GMT+08:00 Arnd Bergmann <arnd@xxxxxxxx>:
>> On Mon, Jan 15, 2018 at 6:53 AM, Greentime Hu <green.hu@xxxxxxxxx> wrote:
>>
>> I had not looked at this patch in enough detail earlier, sorry about
>> that. It should be
>> easy enough to fix though.
>>
>>> +#ifdef CONFIG_VGA_CONSOLE
>>> +struct screen_info screen_info;
>>> +#endif
>>
>> I would assume that you can't ever have a VGA console. Just drop all
>> the references
>> here and instead send a patch to the fbdev maintainer to add the dependency
>> at CONFIG_VGA_CONSOLE to prevent selecting it with nds32.
>
> I found it can be built pass for now because we disable it in defconfig.
> Should I send the patch in v7 series?
yes, I think that would be best.
>>> +
>>> +extern void __init early_init_devtree(void *params);
>>> +extern void __init early_trap_init(void);
>>
>> similarly, these are declared in include/linux/of_fdt.h
>>
>
> early_trap_init is a nds32 function. I will move it to nds32.h
Right, makes sense.
>>> +void calibrate_delay(void)
>>> +{
>>> + const int *val;
>>> + struct device_node *cpu = NULL;
>>> + cpu = of_find_compatible_node(NULL, NULL, "andestech,nds32v3");
>>> + val = of_get_property(cpu, "clock-frequency", NULL);
>>> + if (!val || !*val)
>>> + panic("no cpu 'clock-frequency' parameter in device tree");
>>> + loops_per_jiffy = be32_to_cpup(val) / HZ;
>>> + pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
>>> + loops_per_jiffy / (500000 / HZ),
>>> + (loops_per_jiffy / (5000 / HZ)) % 100, loops_per_jiffy);
>>> +}
>>
>> This seems very odd to me: The 'clock-frequency' property in the
>> cpu node should refer to the actual frequency it is running at, but that
>> tends to be different from the bogomips as needed by the ndelay()
>> function. Can you explain what is going on here?
>>
>
> This implementation is referenced from openrisc.
> https://lkml.org/lkml/2017/11/17/228
It's correct on openrisc, because that has a reliable cycle counter,
and that gets used in its delay function:
void __delay(unsigned long cycles)
{
cycles_t start = get_cycles();
while ((get_cycles() - start) < cycles)
cpu_relax();
}
In my review comment that you cited, I assumed that nds32 had similar
hardware.
However, as you explained earlier, the nds32 architecture does not provide
a cycle counter and the clocksource resolution is not high enough to
be a good replacement, so you have to use the traditional delay
calibration.
Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
