linux-kernel - Re: [PATCH 5/8] staging: rtl8188eu: Remove function rtw

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Date:   Tue, 14 Apr 2020 16:25:51 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Ivan Safonov <insafonov@...il.com>
Cc:     devel@...verdev.osuosl.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nishka Dasgupta <nishkadg.linux@...il.com>,
        Larry Finger <Larry.Finger@...inger.net>
Subject: Re: [PATCH 5/8] staging: rtl8188eu: Remove function rtw_modular64()

On Tue, Apr 14, 2020 at 03:22:59PM +0300, Ivan Safonov wrote:
> 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.

Yeah.  You're right.  I got mixed up and I misread what you were
suggesting.

	tsf = rounddown(pmlmeext->TSFValue, pmlmeinfo->bcn_interval * 1024) - 1024;

regards,
dan carpenter