linux-kernel - Re: [PATCH 2/2] i2c: piix4: Use usleep

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Message-ID: <1518471326.22190.8.camel@perches.com>
Date:   Mon, 12 Feb 2018 13:35:26 -0800
From:   Joe Perches <joe@...ches.com>
To:     Guenter Roeck <linux@...ck-us.net>, Jean Delvare <jdelvare@...e.de>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Zoltán Böszörményi <zboszor@...hu>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] i2c: piix4: Use usleep_range()

On Mon, 2018-02-12 at 12:59 -0800, Guenter Roeck wrote:
> On Mon, Feb 12, 2018 at 11:53:36AM +0100, Jean Delvare wrote:
> > On Sat, 30 Dec 2017 08:50:58 -0800, Guenter Roeck wrote:
> > > The piix4 i2c driver is extremely slow. Replacing msleep()
> > > with usleep_range() increases its speed substantially.
[]
> > > diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
[]
> > > @@ -467,13 +467,13 @@ static int piix4_transaction(struct i2c_adapter *piix4_adapter)
> > >  
> > >  	/* We will always wait for a fraction of a second! (See PIIX4 docs errata) */
> > >  	if (srvrworks_csb5_delay) /* Extra delay for SERVERWORKS_CSB5 */
> > > -		msleep(2);
> > > +		usleep_range(2000, 2000);

usleep_range without a range isn't particularly useful.
Perhaps a 100 uSec range would allow better scheduling.

		usleep_range(2000, 2100);