From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mo1.mail-out.ovh.net ([178.32.228.1]:54397 "EHLO mo1.mail-out.ovh.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751359Ab2LTN1s (ORCPT ); Thu, 20 Dec 2012 08:27:48 -0500 Received: from mail440.ha.ovh.net (b9.ovh.net [213.186.33.59]) by mo1.mail-out.ovh.net (Postfix) with SMTP id A7BE6FFBED5 for ; Thu, 20 Dec 2012 14:03:31 +0100 (CET) Date: Thu, 20 Dec 2012 13:49:09 +0100 From: Jean-Christophe PLAGNIOL-VILLARD To: Maxime Ripard Cc: linux-arm-kernel@lists.infradead.org, linux-iio@vger.kernel.org, Nicolas Ferre , Ludovic Desroches Subject: Re: [PATCH 3/3] ARM: AT91: IIO: fix missing Sample and Hold time Message-ID: <20121220124909.GR23971@game.jcrosoft.org> References: <20121219183236.GP23971@game.jcrosoft.org> <1355942232-26251-1-git-send-email-plagnioj@jcrosoft.com> <1355942232-26251-3-git-send-email-plagnioj@jcrosoft.com> <50D2EEA0.8040807@free-electrons.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: <50D2EEA0.8040807@free-electrons.com> Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On 11:55 Thu 20 Dec , Maxime Ripard wrote: > Hi, > > Le 19/12/2012 19:37, Jean-Christophe PLAGNIOL-VILLARD a écrit : > > On the at91_adc a minimal Sample and Hold Time is necessary for the ADC to > > guarantee the best converted final value between two channels selection. > > This time has to be programmed through the bitfield SHTIM in the > > Mode Register ADC_MR. > > > > Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD > > Cc: linux-iio@vger.kernel.org > > Cc: Nicolas Ferre > > Cc: Ludovic Desroches > > --- > > Documentation/devicetree/bindings/arm/atmel-adc.txt | 1 + > > drivers/iio/adc/at91_adc.c | 15 ++++++++++++++- > > 2 files changed, 15 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/devicetree/bindings/arm/atmel-adc.txt b/Documentation/devicetree/bindings/arm/atmel-adc.txt > > index efb6f02..dd2ca90 100644 > > --- a/Documentation/devicetree/bindings/arm/atmel-adc.txt > > +++ b/Documentation/devicetree/bindings/arm/atmel-adc.txt > > @@ -26,6 +26,7 @@ Optional properties: > > atmel,adc-res-names property. If not specified, the highest > > resolution will be used. > > - atmel,atmel,adc-sleep-mode: Boolean to enable of sleep mode when no conversion > > + - atmel,adc-sample-hold-time: Sample and Hold Time > > In which unit? nanoseconds? number of clock ticks? > > > > > Optional trigger Nodes: > > - Required properties: > > diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c > > index c563488..9481375 100644 > > --- a/drivers/iio/adc/at91_adc.c > > +++ b/drivers/iio/adc/at91_adc.c > > @@ -52,6 +52,7 @@ struct at91_adc_state { > > void __iomem *reg_base; > > struct at91_adc_reg_desc *registers; > > u8 startup_time; > > + u8 sample_hold_time; > > bool sleep_mode; > > struct iio_trigger **trig; > > struct at91_adc_trigger *trigger_list; > > @@ -465,6 +466,9 @@ static int at91_adc_probe_dt(struct at91_adc_state *st, > > } > > st->startup_time = prop; > > > > + prop = 0; > > + of_property_read_u32(node, "atmel,adc-sample-hold-time", &prop); > > + st->sample_hold_time = prop; > > > > if (of_property_read_u32(node, "atmel,adc-vref", &prop)) { > > dev_err(&idev->dev, "Missing adc-vref property in the DT.\n"); > > @@ -578,7 +582,7 @@ static const struct iio_info at91_adc_info = { > > > > static int __devinit at91_adc_probe(struct platform_device *pdev) > > { > > - unsigned int prsc, mstrclk, ticks, adc_clk; > > + unsigned int prsc, mstrclk, ticks, adc_clk, shtim; > > int ret; > > struct iio_dev *idev; > > struct at91_adc_state *st; > > @@ -691,12 +695,21 @@ static int __devinit at91_adc_probe(struct platform_device *pdev) > > */ > > ticks = round_up((st->startup_time * adc_clk / > > 1000000) - 1, 8) / 8; > > + /* > > + * a minimal Sample and Hold Time is necessary for the ADC to guarantee > > + * the best converted final value between two channels selection > > + * The formula thus is : Sample and Hold Time = (shtim + 1) / ADCClock > > + */ > > + shtim = round_up((st->sample_hold_time * adc_clk / > > + 1000000) - 1, 1); > > + > > Since, from all the datasheet I have (G20, G45 and X5), the minimum time > is always 500ns, do we really need to add a dt property for that? you must this is hardware specific it depend on the line capacity Best Regards, J.