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

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Date:	Tue, 18 Oct 2011 11:59:39 +0200
From:	Srinidhi KASAGAR <srinidhi.kasagar@...ricsson.com>
To:	"rpurdie@...ys.net" <rpurdie@...ys.net>
Cc:	"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

Richard,
Did you get a chance to look at this patch?

srinidhi

> -----Original Message-----
> From: Srinidhi KASAGAR
> Sent: Monday, October 10, 2011 5:00 PM
> To: rpurdie@...ys.net
> Cc: linux-kernel@...r.kernel.org; linus.walleij@...aro.org; Srinidhi
> KASAGAR
> Subject: [PATCH] drivers/leds/leds-lp5521.c: check if reset is
> successful
> 
> 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.
> 
> Signed-off-by: srinidhi kasagar <srinidhi.kasagar@...ricsson.com>
> Tested-by: Naga Radhesh <naga.radheshy@...ricsson.com>
> Acked-by: Linus Walleij <linus.walleij@...aro.org>
> ---
>  drivers/leds/leds-lp5521.c |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/leds/leds-lp5521.c b/drivers/leds/leds-lp5521.c
> index 9fc122c..91a2928 100644
> --- a/drivers/leds/leds-lp5521.c
> +++ b/drivers/leds/leds-lp5521.c
> @@ -97,6 +97,9 @@
>  /* Status */
>  #define LP5521_EXT_CLK_USED		0x08
> 
> +/* default R channel current register value */
> +#define LP5521_REG_R_CURR_DEFAULT	0xAF
> +
>  struct lp5521_engine {
>  	int		id;
>  	u8		mode;
> @@ -643,6 +646,7 @@ static int __devinit lp5521_probe(struct i2c_client
> *client,
>  	struct lp5521_chip		*chip;
>  	struct lp5521_platform_data	*pdata;
>  	int ret, i, led;
> +	u8 buf;
> 
>  	chip = kzalloc(sizeof(*chip), GFP_KERNEL);
>  	if (!chip)
> @@ -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);
> +
>  	ret = lp5521_detect(client);
> 
>  	if (ret) {
> --
> 1.7.4.3

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