Messages in this thread | | | Subject | Re: [PATCH 5/8] staging: rtl8188eu: Remove function rtw_modular64() | From | Ivan Safonov <> | Date | Tue, 14 Apr 2020 15:22:59 +0300 |
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On 4/14/20 2:56 PM, Dan Carpenter wrote: > On Sun, Apr 12, 2020 at 04:34:08PM +0300, Ivan Safonov wrote: >>> Remove function rtw_modular64 as all it does is call do_div. >> >> This is wrong. Macro do_div(x, y) change first argument x, but >> rtw_modular64(x, y) preserve it. >> >>> + tsf = pmlmeext->TSFValue - do_div(pmlmeext->TSFValue, (pmlmeinfo->bcn_interval*1024)) - 1024; /* us */ >> >> rounddown(pmlmeext->TSFValue, pmlmeinfo->bcn_interval * 1024) - 1024 >> is a better replacement for > > You're absolutely correct that the patch is buggy, but I'm not sure that > rounddown() is what we want. > > rtw_modular64() took the MOD of x. So it should be something like: > > tsf = pmlmeext->TSFValue - (pmlmeext->TSFValue % (pmlmeinfo->bcn_interval * 1024)) - 1024; /* us */ > > But what the heck is that even??? If pmlmeinfo->bcn_interval is zero > or one then the subtraction ends up giving us a negative. > > regards, > dan carpenter >
1. pmlmeext->TSFValue can not be negative, because it is uint64_t; 2. pmlmeext->TSFValue is cyclic value: https://en.wikipedia.org/wiki/Timing_synchronization_function ; 3. (rounddown(a, b)) is equal to (a - a % b) by definition.
Ivan Safonov.
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