linux-kernel - Re: [PATCH v3 3/3] b43: Use cordic algorithm from kernel library

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Message-ID: <20181117083628.sm6juvz75kiargz4@plaes.org>
Date:   Sat, 17 Nov 2018 08:36:28 +0000
From:   Priit Laes <plaes@...es.org>
To:     Michael Büsch <m@...s.ch>
Cc:     Kees Cook <keescook@...omium.org>,
        Jia-Ju Bai <baijiaju1990@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Larry Finger <Larry.Finger@...inger.net>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Colin Ian King <colin.king@...onical.com>,
        Arend van Spriel <arend.vanspriel@...adcom.com>,
        Varsha Rao <rvarsha016@...il.com>,
        linux-wireless@...r.kernel.org, b43-dev@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] b43: Use cordic algorithm from kernel library

On Wed, Nov 14, 2018 at 07:46:28PM +0100, Michael Büsch wrote:
> On Wed, 14 Nov 2018 20:27:52 +0200
> Priit Laes <plaes@...es.org> wrote:
> 
> > Kernel library has a common cordic algorithm which is identical
> > to internally implementatd one, so use it and drop the duplicate
> > implementation.
> 
> 
> In v2 of the series it has been said that:
> 
> Arend van Spriel <arend.vanspriel@...adcom.com> wrote:
> > I recall doing a comparison between the algorithms and thought I put 
> > that in the original commit message. However, it is not there. It is not 
> > exactly the same as in b43 so there are difference for certain angles, 
> > most results are the same however. This implementation is slightly more 
> > accurate on the full scale.
> 
> 
> That's not my definition of "identical".
> 
> Please do not apply this patch without doing a thorough regression test
> on actual b43 LP hardware.

Indeed, there's a big discrepancy in the results of both algorithms.

Here's the test script:
https://gist.github.com/plaes/284993a4fc65e0926d0628a11f0cf874

So at current state, this is self-NAK from me too and this patch should
be dropped.

> 
> -- 
> Michael