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[80.249.188.84]) by smtp.gmail.com with ESMTPSA id c22sm8980495ljh.66.2020.04.14.05.18.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Apr 2020 05:18:58 -0700 (PDT) Subject: Re: [PATCH 5/8] staging: rtl8188eu: Remove function rtw_modular64() To: Dan Carpenter Cc: Nishka Dasgupta , Larry Finger , Greg Kroah-Hartman , Michael Straube , devel@driverdev.osuosl.org, "linux-kernel@vger.kernel.org" References: <20190712071746.2474-5-nishkadg.linux@gmail.com> <66fb1e37-107e-54f4-4986-ca4e4bb99d2d@yandex.ru> <20200414115604.GF1163@kadam> From: Ivan Safonov Message-ID: <20becb6f-7bf6-8618-9525-b64c226088c7@gmail.com> Date: Tue, 14 Apr 2020 15:22:59 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200414115604.GF1163@kadam> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.