Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754810AbbFQKgK (ORCPT ); Wed, 17 Jun 2015 06:36:10 -0400 Received: from mail-pd0-f175.google.com ([209.85.192.175]:33190 "EHLO mail-pd0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753455AbbFQKfm (ORCPT ); Wed, 17 Jun 2015 06:35:42 -0400 Date: Wed, 17 Jun 2015 16:02:57 +0530 From: maitysanchayan@gmail.com To: Jonathan Cameron Cc: Rob Herring , Shawn Guo , "kernel@pengutronix.de" , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Fugang Duan , "devicetree@vger.kernel.org" , "linux-iio@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Stefan Agner Subject: Re: [PATCH v1 1/2] iio: adc: Determine sampling frequencies by using minimum sample time Message-ID: <20150617103257.GA3174@Sanchayan-Arch> References: <0e624f1c1efff7e209c93406f5d4bc51c41a9f45.1433740528.git.maitysanchayan@gmail.com> <557D6277.3080601@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <557D6277.3080601@kernel.org> User-Agent: Mutt/1.5.23+89 (0255b37be491) (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9475 Lines: 223 Hello, On 15-06-14 12:16:07, Jonathan Cameron wrote: > On 08/06/15 18:51, Rob Herring wrote: > > On Mon, Jun 8, 2015 at 12:42 AM, Sanchayan Maity > > wrote: > >> The driver currently does not take into account the minimum sample time > >> as per the Figure 6-8 Chapter 9.1.1 12-bit ADC electrical characteristics. > >> We set a static amount of cycles instead of considering the sample time as > >> a given value, which depends on hardware characteristics. > >> > >> Determine sampling frequencies by first reading the device tree property > >> node and then calculating the required Long Sample Time Adder (LSTAdder) > >> value based on the ADC clock frequency and sample time value obtained > >> from the device tree, this LSTAdder value is then used for calculating > >> the sampling frequencies possible. > >> > >> Signed-off-by: Sanchayan Maity > >> --- > >> .../devicetree/bindings/iio/adc/vf610-adc.txt | 6 ++ > >> drivers/iio/adc/vf610_adc.c | 74 ++++++++++++++++++++-- > >> 2 files changed, 76 insertions(+), 4 deletions(-) > >> > >> diff --git a/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt b/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt > >> index 3eb40e2..4419126 100644 > >> --- a/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt > >> +++ b/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt > >> @@ -17,6 +17,11 @@ Recommended properties: > >> - Frequency in normal mode (ADLPC=0, ADHSC=0) > >> - Frequency in high-speed mode (ADLPC=0, ADHSC=1) > >> - Frequency in low-power mode (ADLPC=1, ADHSC=0) > >> + - fsl,min-sample-time: Minimum sampling time in nanoseconds. This value has > > > > Add a "-ns' suffix. > > > > Seems like this could be a common ADC property. > Could be but so far this is a first I think... > > Obviously there are constraints on when you'll get a 'good' answer from any > ADC but often they are not so well defined in the datasheets as we have here. > > Having said that, certainly could turn up elsewhere so I've no problem with > having it as normal (non vendor specific) property. Will change this to a non vendor specific property and send v2. Thanks for the review. Regards, Sanchayan. > > > >> + to be chosen according to the conversion mode and the connected analog > >> + source resistance (R_as) and capacitance (C_as). Refer the datasheet's > >> + operating requirements. A safe default across a wide range of R_as and > >> + C_as as well as conversion modes is 1000ns. > >> > >> Example: > >> adc0: adc@4003b000 { > >> @@ -27,5 +32,6 @@ adc0: adc@4003b000 { > >> clock-names = "adc"; > >> fsl,adck-max-frequency = <30000000>, <40000000>, > >> <20000000>; > >> + fsl,min-sample-time = <1000>; > >> vref-supply = <®_vcc_3v3_mcu>; > >> }; > >> diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c > >> index 480f335..bcae8fd 100644 > >> --- a/drivers/iio/adc/vf610_adc.c > >> +++ b/drivers/iio/adc/vf610_adc.c > >> @@ -68,6 +68,9 @@ > >> #define VF610_ADC_CLK_DIV8 0x60 > >> #define VF610_ADC_CLK_MASK 0x60 > >> #define VF610_ADC_ADLSMP_LONG 0x10 > >> +#define VF610_ADC_ADSTS_SHORT 0x100 > >> +#define VF610_ADC_ADSTS_NORMAL 0x200 > >> +#define VF610_ADC_ADSTS_LONG 0x300 > >> #define VF610_ADC_ADSTS_MASK 0x300 > >> #define VF610_ADC_ADLPC_EN 0x80 > >> #define VF610_ADC_ADHSC_EN 0x400 > >> @@ -124,6 +127,17 @@ enum conversion_mode_sel { > >> VF610_ADC_CONV_LOW_POWER, > >> }; > >> > >> +enum lst_adder_sel { > >> + VF610_ADCK_CYCLES_3, > >> + VF610_ADCK_CYCLES_5, > >> + VF610_ADCK_CYCLES_7, > >> + VF610_ADCK_CYCLES_9, > >> + VF610_ADCK_CYCLES_13, > >> + VF610_ADCK_CYCLES_17, > >> + VF610_ADCK_CYCLES_21, > >> + VF610_ADCK_CYCLES_25, > >> +}; > >> + > >> struct vf610_adc_feature { > >> enum clk_sel clk_sel; > >> enum vol_ref vol_ref; > >> @@ -132,6 +146,8 @@ struct vf610_adc_feature { > >> int clk_div; > >> int sample_rate; > >> int res_mode; > >> + u32 lst_adder_index; > >> + u32 default_sample_time; > >> > >> bool calibration; > >> bool ovwren; > >> @@ -155,11 +171,13 @@ struct vf610_adc { > >> }; > >> > >> static const u32 vf610_hw_avgs[] = { 1, 4, 8, 16, 32 }; > >> +static const u32 vf610_lst_adder[] = { 3, 5, 7, 9, 13, 17, 21, 25 }; > >> > >> static inline void vf610_adc_calculate_rates(struct vf610_adc *info) > >> { > >> struct vf610_adc_feature *adc_feature = &info->adc_feature; > >> unsigned long adck_rate, ipg_rate = clk_get_rate(info->clk); > >> + u32 adck_period, lst_addr_min; > >> int divisor, i; > >> > >> adck_rate = info->max_adck_rate[adc_feature->conv_mode]; > >> @@ -174,6 +192,19 @@ static inline void vf610_adc_calculate_rates(struct vf610_adc *info) > >> } > >> > >> /* > >> + * Determine the long sample time adder value to be used based > >> + * on the default minimum sample time provided. > >> + */ > >> + adck_period = NSEC_PER_SEC / adck_rate; > >> + lst_addr_min = adc_feature->default_sample_time / adck_period; > >> + for (i = 0; i < ARRAY_SIZE(vf610_lst_adder); i++) { > >> + if (vf610_lst_adder[i] > lst_addr_min) { > >> + adc_feature->lst_adder_index = i; > >> + break; > >> + } > >> + } > >> + > >> + /* > >> * Calculate ADC sample frequencies > >> * Sample time unit is ADCK cycles. ADCK clk source is ipg clock, > >> * which is the same as bus clock. > >> @@ -182,12 +213,13 @@ static inline void vf610_adc_calculate_rates(struct vf610_adc *info) > >> * SFCAdder: fixed to 6 ADCK cycles > >> * AverageNum: 1, 4, 8, 16, 32 samples for hardware average. > >> * BCT (Base Conversion Time): fixed to 25 ADCK cycles for 12 bit mode > >> - * LSTAdder(Long Sample Time): fixed to 3 ADCK cycles > >> + * LSTAdder(Long Sample Time): 3, 5, 7, 9, 13, 17, 21, 25 ADCK cycles > >> */ > >> adck_rate = ipg_rate / info->adc_feature.clk_div; > >> for (i = 0; i < ARRAY_SIZE(vf610_hw_avgs); i++) > >> info->sample_freq_avail[i] = > >> - adck_rate / (6 + vf610_hw_avgs[i] * (25 + 3)); > >> + adck_rate / (6 + vf610_hw_avgs[i] * > >> + (25 + vf610_lst_adder[adc_feature->lst_adder_index])); > >> } > >> > >> static inline void vf610_adc_cfg_init(struct vf610_adc *info) > >> @@ -347,8 +379,40 @@ static void vf610_adc_sample_set(struct vf610_adc *info) > >> break; > >> } > >> > >> - /* Use the short sample mode */ > >> - cfg_data &= ~(VF610_ADC_ADLSMP_LONG | VF610_ADC_ADSTS_MASK); > >> + /* > >> + * Set ADLSMP and ADSTS based on the Long Sample Time Adder value > >> + * determined. > >> + */ > >> + switch (adc_feature->lst_adder_index) { > >> + case VF610_ADCK_CYCLES_3: > >> + break; > >> + case VF610_ADCK_CYCLES_5: > >> + cfg_data |= VF610_ADC_ADSTS_SHORT; > >> + break; > >> + case VF610_ADCK_CYCLES_7: > >> + cfg_data |= VF610_ADC_ADSTS_NORMAL; > >> + break; > >> + case VF610_ADCK_CYCLES_9: > >> + cfg_data |= VF610_ADC_ADSTS_LONG; > >> + break; > >> + case VF610_ADCK_CYCLES_13: > >> + cfg_data |= VF610_ADC_ADLSMP_LONG; > >> + break; > >> + case VF610_ADCK_CYCLES_17: > >> + cfg_data |= VF610_ADC_ADLSMP_LONG; > >> + cfg_data |= VF610_ADC_ADSTS_SHORT; > >> + break; > >> + case VF610_ADCK_CYCLES_21: > >> + cfg_data |= VF610_ADC_ADLSMP_LONG; > >> + cfg_data |= VF610_ADC_ADSTS_NORMAL; > >> + break; > >> + case VF610_ADCK_CYCLES_25: > >> + cfg_data |= VF610_ADC_ADLSMP_LONG; > >> + cfg_data |= VF610_ADC_ADSTS_NORMAL; > >> + break; > >> + default: > >> + dev_err(info->dev, "error in sample time select\n"); > >> + } > >> > >> /* update hardware average selection */ > >> cfg_data &= ~VF610_ADC_AVGS_MASK; > >> @@ -712,6 +776,8 @@ static int vf610_adc_probe(struct platform_device *pdev) > >> > >> of_property_read_u32_array(pdev->dev.of_node, "fsl,adck-max-frequency", > >> info->max_adck_rate, 3); > >> + of_property_read_u32(pdev->dev.of_node, "fsl,min-sample-time", > >> + &info->adc_feature.default_sample_time); > >> > >> platform_set_drvdata(pdev, indio_dev); > >> > >> -- > >> 2.4.2 > >> > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-iio" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/