On Fri, Nov 17, 2017 at 1:39 PM, Greentime Hu [off-list ref] wrote:

2017-11-10 16:26 GMT+08:00 Greentime Hu [off-list ref]:

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2017-11-09 18:33 GMT+08:00 Arnd Bergmann [off-list ref]:

quoted

On Thu, Nov 9, 2017 at 10:02 AM, Greentime Hu [off-list ref] wrote:

quoted

2017-11-08 18:16 GMT+08:00 Arnd Bergmann [off-list ref]:

quoted

On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu [off-list ref] wrote:

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+config GENERIC_CALIBRATE_DELAY
+       def_bool y

It's better to avoid the delay loop completely and skip the calibration,
if your hardware allows.

Thanks.
Do you mean that this config should be def_bool n?
why? Almost all arch enable it.

It depends on what your hardware can do. If you have a way to see how much
time has passed that is guaranteed to be reliable on all machines, then
use that instead.

On a lot of architectures, it's not possible, so they have to fall back to using
the delay loop.

I get it. I will discuss it with our HW colleagues.
We may get these informations in some registers.

Hi, Arnd:

I think I can't set it to default n because it will be called in start_kernel.

start_kernel() -> calibrate_delay()

If I don't enable this config, it will link error because it didn't
build init/calibrate.c

You will have to provide an architecture-specific implementation of
this function, please ahve a look at what others are doing, e.g. tile,
openrisc or
h8300.

          Arnd