linux-kernel - Re: [RESEND PATCH v5 3/5] IIO: Ingenic JZ47xx: Add touchscreen mode.

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Date:   Sun, 19 Apr 2020 14:19:26 +0200
From:   Artur Rojek <contact@...ur-rojek.eu>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Cameron <jic23@...nel.org>,
        Paul Cercueil <paul@...pouillou.net>,
        Heiko Stuebner <heiko@...ech.de>,
        linux-input <linux-input@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v5 3/5] IIO: Ingenic JZ47xx: Add touchscreen mode.

Hi Andy,
thanks for the review. Comments inline.

On 2020-04-17 22:59, Andy Shevchenko wrote:
> On Fri, Apr 17, 2020 at 11:21 PM Artur Rojek <contact@...ur-rojek.eu> 
> wrote:
>> 
>> The SADC component in JZ47xx SoCs provides support for touchscreen
>> operations (pen position and pen down pressure) in single-ended and
>> differential modes.
>> 
>> Of the known hardware to use this controller, GCW Zero and Anbernic 
>> RG-350
>> utilize the touchscreen mode by having their joystick(s) attached to 
>> the
>> X/Y positive/negative input pins.
>> GCW Zero comes with a single joystick and is sufficiently handled with 
>> the
>> currently implemented single-ended mode. Support for boards with two
>> joysticks, where one is hooked up to Xn/Yn and the other to Xp/Yp 
>> channels
>> will need to be provided in the future.
>> 
>> The touchscreen component of SADC takes a significant time to 
>> stabilize
>> after first receiving the clock and a delay of 50ms has been 
>> empirically
>> proven to be a safe value before data sampling can begin.
>> 
>> All the boards which probe this driver have the interrupt provided 
>> from
>> devicetree, with no need to handle a case where the irq was not 
>> provided.
> 
> Device Tree
> IRQ
> 
> ...
> 
>> +               .scan_type = {
>> +                       .sign = 'u',
>> +                       .realbits = 12,
> 
>> +                       .storagebits = 16
> 
> It's slightly better to leave comma in such cases.
> 
>> +               },
> 
>> +               .scan_type = {
>> +                       .sign = 'u',
>> +                       .realbits = 12,
> 
>> +                       .storagebits = 16
> 
> Ditto.
> 
>> +               },
> 
> ...
> 
>>                 .indexed = 1,
>>                 .channel = INGENIC_ADC_AUX,
>> +               .scan_index = -1
> 
> Ditto. You see above? Isn't it nice that you didn't touch that line?
> So, perhaps next developer can leverage this subtle kind of things.
> 
>>                 .indexed = 1,
>>                 .channel = INGENIC_ADC_BATTERY,
>> +               .scan_index = -1
> 
> Ditto.
> 
>>                 .indexed = 1,
>>                 .channel = INGENIC_ADC_AUX2,
>> +               .scan_index = -1
> 
> Ditto.
> 
> ...
> 
>> +static int ingenic_adc_buffer_enable(struct iio_dev *iio_dev)
>> +{
>> +       struct ingenic_adc *adc = iio_priv(iio_dev);
>> +
> 
>> +       clk_enable(adc->clk);
> 
> Error check?
> 
>> +       /* It takes significant time for the touchscreen hw to 
>> stabilize. */
>> +       msleep(50);
>> +       ingenic_adc_set_config(adc, JZ_ADC_REG_CFG_TOUCH_OPS_MASK,
>> +                              JZ_ADC_REG_CFG_SAMPLE_NUM(4) |
>> +                              JZ_ADC_REG_CFG_PULL_UP(4));
>> +       writew(80, adc->base + JZ_ADC_REG_ADWAIT);
>> +       writew(2, adc->base + JZ_ADC_REG_ADSAME);
> 
>> +       writeb((u8)~JZ_ADC_IRQ_TOUCH, adc->base + JZ_ADC_REG_CTRL);
> 
> Why casting?
After flipping the bits, the resulting value can't be represented by u8. 
Since we care only about the first 8 bits anyway, explicit cast here is 
to silence a compiler warning.
> 
>> +       writel(0, adc->base + JZ_ADC_REG_ADTCH);
>> +       ingenic_adc_enable(adc, 2, true);
>> +
>> +       return 0;
>> +}
> 
>> +       irq = platform_get_irq(pdev, 0);
> 
> Before it worked w/o IRQ, here is a regression you introduced.
> 
>> +       if (irq < 0) {
> 
>> +               dev_err(dev, "Failed to get irq: %d\n", irq);
> 
> Redundant message.
> 
>> +               return irq;
>> +       }

- Artur