Re: [Linuxptp-users] Overflow issue for 32bit machines: ptp_clock_info.max_adj versus timex.freq

[Janusz U. <j.u...@el...>]

More details:
The type of "freq" field in "__kernel_timex" structure is fixed in 
mainline kernel to "long long" type.
However "__kernel_long_t freq" in timex structure depends on machine.
Eg. for some machines it see:
include/uapi/asm-generic/posix_types.h:typedef long __kernel_long_t;
arch/sparc/include/uapi/asm/posix_types.h: typedef long __kernel_long_t;

best regards
Janusz Uzycki


W dniu 06/10/2022 o 00:11, Janusz Użycki pisze:
> Hi.
>
> A lot of PTP/PHC drivers set max_adj value quite big. Howover due to 
> kernel's API limit of 32bit long type value (freq) and POSIX frequency 
> conversion it should limited to 32767999 ppb.
>
> It concerns the frequency limit check both for kernel, testptp and 
> ptp4linux servos. Simply 65.536 * 32767999 is almost 2^31... It is 
> also common for adjfreq() vs newer adjfine().
> Moreover such big frequency limits seem not practical (phase jump used 
> instead, 1000ppm is huge for any PTP oscillator application), even 
> driver or rather PHC hardware has ability to tune is such range.
>
>
> best regards
> Janusz Uzycki
>
>