[U-Boot] [PATCH v2 5/9] arm: exynos: Wait till ADC stabilizes before checking Odroid HC1 revision

[Lukasz Majewski <lukma@denx.de>]

On Wed, 13 Feb 2019 17:46:44 +0100
Krzysztof Kozlowski <krzk@kernel.org> wrote:

> Fix detection of Odroid HC1 (Exynos5422) after reboot if kernel
> disabled the LDO4/VDD_ADC regulator.
> 
> The LDO4 supplies both ADC block and the ADC input AIN9.  Voltage on
> AIN9 will rise slowly, so be patient and wait for it to stabilize.
> 
> First reads on Odroid HC1 return 305, 1207, 1297 and finally 1308
> (reference value is 1309).
> 
> Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
> ---
>  board/samsung/common/exynos5-dt-types.c | 38
> ++++++++++++++++++++++++- 1 file changed, 37 insertions(+), 1
> deletion(-)
> 
> diff --git a/board/samsung/common/exynos5-dt-types.c
> b/board/samsung/common/exynos5-dt-types.c index
> af711e727a78..8aed64183837 100644 ---
> a/board/samsung/common/exynos5-dt-types.c +++
> b/board/samsung/common/exynos5-dt-types.c @@ -57,12 +57,48 @@ static
> unsigned int odroid_get_rev(void) return 0;
>  }
>  
> +/*
> + * Read ADC at least twice and check the resuls.  If regulator
> providing voltage
> + * on to measured point was just turned on, first reads might
> require time
> + * to stabilize.
> + */
> +static int odroid_get_adc_val(unsigned int *adcval)
> +{
> +	unsigned int adcval_prev = 0;
> +	int ret, retries = 20;
> +
> +	ret = adc_channel_single_shot("adc", CONFIG_ODROID_REV_AIN,
> +				      &adcval_prev);
> +	if (ret)
> +		return ret;
> +
> +	while (retries--) {
> +		mdelay(5);
> +
> +		ret = adc_channel_single_shot("adc",
> CONFIG_ODROID_REV_AIN,
> +					      adcval);
> +		if (ret)
> +			return ret;
> +
> +		/*
> +		 * If difference between ADC reads is less than 3%,
> +		 * accept the result
> +		 */
> +		if ((100 * abs(*adcval - adcval_prev) / adcval_prev)
> < 3)
> +			return ret;
> +
> +		adcval_prev = *adcval;
> +	}

Is there in the documentation any required time to wait before reading
the ADC value?

If yes then maybe get_timer() based approach shall be used (if
get_timer() is available in this context)?

Please see for example drivers/net/fec_mxc.c for how timeouts are
handled there.

I will test this patch series on XU3 during the weekend. Thanks for
this fix :-) 

> +
> +	return ret;
> +}
> +
>  static int odroid_get_board_type(void)
>  {
>  	unsigned int adcval;
>  	int ret, i;
>  
> -	ret = adc_channel_single_shot("adc", CONFIG_ODROID_REV_AIN,
> &adcval);
> +	ret = odroid_get_adc_val(&adcval);
>  	if (ret)
>  		goto rev_default;
>  




Best regards,

Lukasz Majewski

--

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