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

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Message-Id: <20111018141048.1f38b211.akpm@linux-foundation.org>
Date:	Tue, 18 Oct 2011 14:10:48 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Srinidhi KASAGAR <srinidhi.kasagar@...ricsson.com>
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!
	 */

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