linux-kernel - Re: [PATCH 7/9 -v2] imx: serial: use rational library function

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Message-ID: <20090615081516.GB31396@pengutronix.de>
Date:	Mon, 15 Jun 2009 10:15:16 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Oskar Schirmer <os@...ix.com>
Cc:	Sascha Hauer <kernel@...gutronix.de>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 7/9 -v2] imx: serial: use rational library function

On Mon, Jun 15, 2009 at 09:40:33AM +0200, Oskar Schirmer wrote:
> On Fri, Jun 12, 2009 at 09:16:49 +0200, Sascha Hauer wrote:
> > Hi Oskar,
> > 
> > On Wed, Jun 10, 2009 at 02:08:34PM +0200, Oskar Schirmer wrote:
> > > for calculation of numerator and denominator
> > > used in baud rate setting, use generic library function
> > > for optimum settings.
> > > 
> > > Signed-off-by: Oskar Schirmer <os@...ix.com>
> > > ---
> > >  drivers/serial/Kconfig |    1 +
> > >  drivers/serial/imx.c   |   30 ++++++++++--------------------
> > >  2 files changed, 11 insertions(+), 20 deletions(-)
> > > 
> > > diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
> > > index 343e3a3..0ecb4c4 100644
> > > --- a/drivers/serial/Kconfig
> > > +++ b/drivers/serial/Kconfig
> > > @@ -833,6 +833,7 @@ config SERIAL_IMX
> > >  	bool "IMX serial port support"
> > >  	depends on ARM && (ARCH_IMX || ARCH_MXC)
> > >  	select SERIAL_CORE
> > > +	select RATIONAL
> > >  	help
> > >  	  If you have a machine based on a Motorola IMX CPU you
> > >  	  can enable its onboard serial port by enabling this option.
> > > diff --git a/drivers/serial/imx.c b/drivers/serial/imx.c
> > > index 60892a2..11f93e2 100644
> > > --- a/drivers/serial/imx.c
> > > +++ b/drivers/serial/imx.c
> > > @@ -41,6 +41,7 @@
> > >  #include <linux/serial_core.h>
> > >  #include <linux/serial.h>
> > >  #include <linux/clk.h>
> > > +#include <linux/rational.h>
> > >  
> > >  #include <asm/io.h>
> > >  #include <asm/irq.h>
> > > @@ -670,7 +671,8 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
> > >  	unsigned long flags;
> > >  	unsigned int ucr2, old_ucr1, old_txrxen, baud, quot;
> > >  	unsigned int old_csize = old ? old->c_cflag & CSIZE : CS8;
> > > -	unsigned int div, num, denom, ufcr;
> > > +	unsigned int div, ufcr;
> > > +	unsigned long num, denom;
> > >  
> > >  	/*
> > >  	 * If we don't support modem control lines, don't allow
> > > @@ -772,32 +774,20 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
> > >  	if (!div)
> > >  		div = 1;
> > >  
> > > -	num = baud;
> > > -	denom = port->uartclk / div / 16;
> > > +	rational_best_approximation(16 * div * baud, sport->port.uartclk,
> > > +		1 << 16, 1 << 16, &num, &denom);
> > 
> > Reading the example you have given for rational_best_approximation() in
> > the last patch this should be (1 << 16) - 1, right?
> 
> No, the registers hold values minus one, e.g.
> to select numerator = 14, set UBIR = 13.
> Thus, the maximum value for rate calculation
> is 1 << 16, not 0xFFFF. For the "minus 1", see below.

Ah, I see.
I'm fine with this patch and the rest of the series. so applied to
mxc-master.

Sascha

> 
> > 
> > >  
> > > -	/* shift num and denom right until they fit into 16 bits */
> > > -	while (num > 0x10000 || denom > 0x10000) {
> > > -		num >>= 1;
> > > -		denom >>= 1;
> > > -	}
> > > -	if (num > 0)
> > > -		num -= 1;
> > > -	if (denom > 0)
> > > -		denom -= 1;
> > > -
> > > -	writel(num, sport->port.membase + UBIR);
> > > -	writel(denom, sport->port.membase + UBMR);
> > > -
> > > -	if (div == 7)
> > > -		div = 6; /* 6 in RFDIV means divide by 7 */
> > > -	else
> > > -		div = 6 - div;
> > > +	num -= 1;
> > > +	denom -= 1;
> 
> This is where rate calculation values are
> decreased for register purpose.
> 
> > >  
> > >  	ufcr = readl(sport->port.membase + UFCR);
> > >  	ufcr = (ufcr & (~UFCR_RFDIV)) |
> > >  	    (div << 7);
> > >  	writel(ufcr, sport->port.membase + UFCR);
> > >  
> > > +	writel(num, sport->port.membase + UBIR);
> > > +	writel(denom, sport->port.membase + UBMR);
> > > +
> > >  #ifdef ONEMS
> > >  	writel(sport->port.uartclk / div / 1000, sport->port.membase + ONEMS);
> > >  #endif
> > > -- 
> > > 1.5.3.7
> > > 
> > > 
> > 
> > -- 
> > Pengutronix e.K.                           |                             |
> > Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> > Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> > Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
> > 
> 
> -- 
> oskar schirmer, emlix gmbh, http://www.emlix.com
> fon +49 551 30664-0, fax -11, bahnhofsallee 1b, 37081 göttingen, germany
> geschäftsführung: dr. uwe kracke, dr. cord seele, ust-idnr.: de 205 198 055
> sitz der gesellschaft: göttingen, amtsgericht göttingen hr b 3160
> 
> emlix - your embedded linux partner
> 

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