Re: [PATCH v2 0/4] clock: Get rid of clock_get_ns()

[Philippe Mathieu-Daudé]

On 12/15/20 4:09 PM, Peter Maydell wrote:
> This patchseries makes some changes to the clock API:
>  * Remove clock_get_ns()
>  * Add clock_ticks_to_ns() to return number of nanoseconds
>    it will take the clock to tick N times
>  * clock_display_freq() to return prettily-formatted string
>    for showing humans the approximate clock frequency
> 
> This is based on discussions we had about these APIs a little while
> back.  The core driver here is that the clock objects internally
> store the period in units of 2^-32 ns, so both clock_get_ns() and
> clock_get_hz() are inherently returning a rounded-off result, which
> can be badly inaccurate for fast clocks or if you want to multiply it
> by a large tick count.
> 
> Ideally I'd like to get rid of clock_get_hz() as well, but
> that looks trickier than handling clock_get_ns().
> 
> Patch 4 borrows a lot of the concept from one of Philippe's that he
> sent out previously.
> 
> NB: tested with 'make check' and 'make check-acceptance' only.

Tested using loongson3-virt @2GHz
https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg04036.html

Without your series:
qemu-system-mips64el: target/mips/cpu.c:385: mips_cp0_period_set:
Assertion `env->cp0_count_ns' failed.
Aborted (core dumped)

With: OK (cpu are not displayed in 'info qtree).

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Thanks!

Phil.