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

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Date:   Tue, 14 Apr 2020 14:56:05 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Ivan Safonov <isaf21@...dex.ru>
Cc:     Nishka Dasgupta <nishkadg.linux@...il.com>,
        Larry Finger <Larry.Finger@...inger.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Straube <straube.linux@...il.com>,
        devel@...verdev.osuosl.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] staging: rtl8188eu: Remove function rtw_modular64()

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