Return-path: Received: from mail-wi0-f179.google.com ([209.85.212.179]:36735 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751095AbbEYIXz convert rfc822-to-8bit (ORCPT ); Mon, 25 May 2015 04:23:55 -0400 Received: by wizk4 with SMTP id k4so41065650wiz.1 for ; Mon, 25 May 2015 01:23:54 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1432282693-4553-1-git-send-email-michal.kazior@tieto.com> Date: Mon, 25 May 2015 10:23:54 +0200 Message-ID: (sfid-20150525_102359_758879_EBF65C2E) Subject: Re: [PATCH v3 1/2] ath10k: handle cycle counter wraparound From: Michal Kazior To: Srinivasa Duvvuri Cc: "ath10k@lists.infradead.org" , linux-wireless Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 22 May 2015 at 19:11, Srinivasa Duvvuri wrote: > Michal, > Sorry I was out sick last few days. Thanks for splitting and creating 2 > patches. > The math for total cycle counts makes sense but the math to handle the > rx_clear_count > does not seem right to me. For the total cycle count we know that the > count changes > from 0xffffffff to 0x7fffffff. So, we clearly know the wrap around point > . But for > rcc( rx_clear_count) we do not know when this count is halfed (wrapped). > > Lets say rcc_prev is the previous clear cycle count, rcc is the current > clear cycle count > and rcc_wrap is a point at which the the total cycle count is wrapped > from 0xfffffffff to 0x7fffffff . > At that point the rcc_wrap resets to rcc_wrap/2. > > Here is how counts wrap around. > > cc_prev ............0xffffffff -> 0x7fffffff ................ cc > rcc_prev ............rcc_wrap -> rcc_wrap/2 ........... rcc. > > The right math to calculate rcc_delta would be (rcc_wrap - rcc_prev) + > (rcc - rcc_wrap/2). > To do the math, we need the rcc_wrap which we do not have. > the patch seems to simply do 2*rcc - rcc_prev . Unless I am missing > something, > this does not seem right to me. Ah, you're right. I guess I'll need to discard the data like you originally did upon wraparound detection. Michał