netdev - RE: [PATCH 1/2] can: rcar_can: Add r8a7795 support

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Date:	Mon, 29 Feb 2016 14:06:21 +0000
From:	Ramesh Shanmugasundaram <ramesh.shanmugasundaram@...renesas.com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>,
	"wg@...ndegger.com" <wg@...ndegger.com>,
	"horms@...ge.net.au" <horms@...ge.net.au>,
	"magnus.damm@...il.com" <magnus.damm@...il.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>
CC:	"linux-renesas-soc@...r.kernel.org" 
	<linux-renesas-soc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Chris Paterson <Chris.Paterson2@...esas.com>
Subject: RE: [PATCH 1/2] can: rcar_can: Add r8a7795 support

Hi Marc,

> On 02/29/2016 11:00 AM, Marc Kleine-Budde wrote:
> > I think it's better to fix the algorithm. I'll look into it.
> 
> What about:
> 
> > ./can-calc-bit-timing -c 39999998 rcar_can
> > Bit timing parameters for rcar_can with 39.999998 MHz ref clock
> > nominal                                 real Bitrt   nom  real SampP
> > Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error
> CiBCR
> > 1000000    125   2    3    2   1   5  999999  0.0% 75.0% 75.0%  0.0%
> 0x40040100
> >  800000    125   3    4    2   1   5  799999  0.0% 80.0% 80.0%  0.0%
> 0x60040100
> >  500000    125   6    7    2   1   5  499999  0.0% 87.5% 87.5%  0.0%
> 0xc0040100
> >  250000    250   6    7    2   1  10  249999  0.0% 87.5% 87.5%  0.0%
> 0xc0090100
> >  125000    500   6    7    2   1  20  124999  0.0% 87.5% 87.5%  0.0%
> 0xc0130100
> >  100000    625   6    7    2   1  25   99999  0.0% 87.5% 87.5%  0.0%
> 0xc0180100
> >   50000   1250   6    7    2   1  50   49999  0.0% 87.5% 87.5%  0.0%
> 0xc0310100
> >   20000   3125   6    7    2   1 125   19999  0.0% 87.5% 87.5%  0.0%
> 0xc07c0100
> >   10000   6250   6    7    2   1 250    9999  0.0% 87.5% 87.5%  0.0%
> 0xc0f90100
> 

I think, it should be correct. Can I have the patch please(can-utils or kernel)? I'll give it a go.

Manual e.g. shows, for 1Mbps and 40MHz clock, two settings are possible
10Tq -> BRP 4
20Tq -> BRP 2

Condition is TSEG1 > TSEG2 >= SJW & bitrate = clock freq/(brp * number of Tq)

Your e.g. satisfies the condition and hopefully it should be OK.

Thanks,
Ramesh