linux-kernel - Re: [PATCH] drivers: mfd: ti_am335x_tscadc: increase ADC ref clock to 24MHz

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Date:   Fri, 11 Nov 2016 11:47:19 +0530
From:   Vignesh R <vigneshr@...com>
To:     John Syne <john3909@...il.com>
CC:     Lee Jones <lee.jones@...aro.org>,
        "N, Mugunthan V" <mugunthanvnm@...com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>,
        Jonathan Cameron <jic23@...nel.org>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Nori, Sekhar" <nsekhar@...com>,
        "Ujfalusi, Peter" <peter.ujfalusi@...com>
Subject: Re: [PATCH] drivers: mfd: ti_am335x_tscadc: increase ADC ref clock to
 24MHz



On Friday 11 November 2016 09:00 AM, John Syne wrote:
> 
>> On Nov 9, 2016, at 9:07 PM, Vignesh R <vigneshr@...com> wrote:
>>
>> Hi,
>>
>> On Thursday 10 November 2016 05:23 AM, John Syne wrote:
>>> OK, then back to my original question. Given that these DT properties are supported in the driver
>>>
>>
>> Below properties are supported by only by ti_am3335x_adc driver and not
>> ti_am335x_tsc driver. As author of this patch pointed out in another
>> reply, there is no need to change step-opendelay for tsc. AFAIK, I don't
>> see a use case where these values needs to be tweaked for tsc channels,
>> therefore it does not make sense to be DT properties.
> Yeah, the confusion was mine because the author of this patch series was proposing to hard code these settings while DT properties already existed in the ti_am335x_adc driver. I use the ADC for sensor measurement and do not use the touchscreen features. I already pointed out where these DT parameters should be added by referencing how this was done in one of the BBB DT overlay files [1]. I am just proposing the same is done as a default in the AM33xx.dtsi and AM4372.dtsi files. Here is what I was proposing. 

> Granted, the adc-channels should be restricted to the subset of channels not used by tsc, but you get the idea.

There are 4 wire, 5 wire and 8 wire touchscreens. Therefore there is no
way to know in advance, how many channels are available for adc. IMO,
this is not a SoC specific configuration but board dependent. Hence, all
channel related configurations need to be in board specific dts files
and not in top level dtsi files.

> 
> tscadc: tscadc@...0d000 {
> 			compatible = "ti,am3359-tscadc";
> 			reg = <0x44e0d000 0x1000>;
> 			interrupt-parent = <&intc>;
> 			interrupts = <16>;
> 			ti,hwmods = "adc_tsc";
> 			status = "disabled";
> 			dmas = <&edma 53 0>, <&edma 57 0>;
> 			dma-names = "fifo0", "fifo1”;
> 
> 			tsc {
> 				compatible = "ti,am3359-tsc";
> 			};
> 			am335x_adc: adc {
> 				#io-channel-cells = <1>;
> 				ti,adc-channels = <0 1 2 3 4 5 6>;
> 				ti,chan-step-avg = <0x16 0x16 0x16 0x16 0x16 0x16 0x16>;
> 				ti,chan-step-opendelay = <0x98 0x98 0x98 0x98 0x98 0x98 0x98>;
> 				ti,chan-step-sampledelay = <0x0 0x0 0x0 0x0 0x0 0x0 0x0>;
> 				compatible = "ti,am3359-adc";
> 			};
> };
> 
> [1]https://github.com/RobertCNelson/bb.org-overlays/blob/master/src/arm/BB-ADC-00A0.dts
> 

-- 
Regards
Vignesh