linux-kernel - RE: [PATCH] drivers/leds/leds-lp5521.c: check if reset is successful

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Message-ID: <C832F8F5D375BD43BFA11E82E0FE9FE00DC2FE2615@EXDCVYMBSTM005.EQ1STM.local>
Date:	Wed, 19 Oct 2011 06:33:18 +0200
From:	Srinidhi KASAGAR <srinidhi.kasagar@...ricsson.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"rpurdie@...ys.net" <rpurdie@...ys.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>
Subject: RE: [PATCH] drivers/leds/leds-lp5521.c: check if reset is successful


> -----Original Message-----
> From: Andrew Morton [mailto:akpm00@...il.com] On Behalf Of Andrew
> Morton
> Sent: Wednesday, October 19, 2011 2:41 AM
> To: Srinidhi KASAGAR
> Cc: rpurdie@...ys.net; linux-kernel@...r.kernel.org;
> linus.walleij@...aro.org
> Subject: Re: [PATCH] drivers/leds/leds-lp5521.c: check if reset is
> successful
> 
> On Mon, 10 Oct 2011 17:00:02 +0530
> Srinidhi KASAGAR <srinidhi.kasagar@...ricsson.com> wrote:
> 
> > make sure that the reset is successful by issuing a dummy
> > read to R channel current register and check its default
> > value. On some platforms, without this dummy read, any
> > further access to {R/G/B}_EXEC will not have any impact.
> >
> > ...
> >
> > @@ -681,6 +685,21 @@ static int __devinit lp5521_probe(struct
> i2c_client *client,
> >  				     * Exact value is not available. 10 - 20ms
> >  				     * appears to be enough for reset.
> >  				     */
> > +
> > +	/*
> > +	 * Make sure that the chip is reset by reading back
> > +	 * r channel current reg. This is a dummy read, otherwise
> > +	 * in some platforms, access to R G B channel program
> > +	 * execution mode to 'Run' in LP5521_REG_ENABLE register
> > +	 * will not have any affect - strange!
> > +	 */
> > +	lp5521_read(client, LP5521_REG_R_CURRENT, &buf);
> > +	if (buf != LP5521_REG_R_CURR_DEFAULT) {
> > +		dev_err(&client->dev, "error in reseting chip\n");
> > +		goto fail2;
> > +	}
> > +	usleep_range(10000, 20000);
> 
> Sorry, but I found that comment very hard to follow.
> 
> Is this version accurate and complete?
> 
> 	/*
> 	 * Make sure that the chip is reset by reading back the r channel
> 	 * current reg. This dummy read is required on some platforms -
> 	 * otherwise further access to the R G B channels in the
> 	 * LP5521_REG_ENABLE register will not have any effect - strange!
> 	 */

That should be ok.

Thanks Andrew.

Srinidhi
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