netdev - Re: [PATCH v5 1/2] wilc1000: Add reset/enable GPIO support to SPI driver

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Message-ID: <0d3a6f22-1ab4-a93d-1fea-8763546db291@microchip.com>
Date:   Thu, 16 Dec 2021 07:08:55 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <davidm@...uge.net>, <Ajay.Kathat@...rochip.com>
CC:     <adham.abozaeid@...rochip.com>, <davem@...emloft.net>,
        <devicetree@...r.kernel.org>, <kuba@...nel.org>,
        <kvalo@...eaurora.org>, <linux-kernel@...r.kernel.org>,
        <linux-wireless@...r.kernel.org>, <netdev@...r.kernel.org>,
        <robh+dt@...nel.org>
Subject: Re: [PATCH v5 1/2] wilc1000: Add reset/enable GPIO support to SPI
 driver

On 15.12.2021 16:59, David Mosberger-Tang wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Wed, 2021-12-15 at 06:41 +0000, Claudiu.Beznea@...rochip.com wrote:
>> On 15.12.2021 05:05, David Mosberger-Tang wrote:
>>>
>> +static int wilc_parse_gpios(struct wilc *wilc)
>>> +{
>>> +       struct spi_device *spi = to_spi_device(wilc->dev);
>>> +       struct wilc_spi *spi_priv = wilc->bus_data;
>>> +       struct wilc_gpios *gpios = &spi_priv->gpios;
>>> +
>>> +       /* get ENABLE pin and deassert it (if it is defined): */
>>> +       gpios->enable = devm_gpiod_get_optional(&spi->dev,
>>> +                                               "enable", GPIOD_OUT_LOW);
>>> +       /* get RESET pin and assert it (if it is defined): */
>>> +       if (gpios->enable) {
>>> +               /* if enable pin exists, reset must exist as well */
>>> +               gpios->reset = devm_gpiod_get(&spi->dev,
>>> +                                             "reset", GPIOD_OUT_HIGH);
>>
>> As far as I can tell form gpiolib code the difference b/w GPIOD_OUT_HIGH
>> and GPIOD_OUT_LOW in gpiolib is related to the initial value for the GPIO.
> 
> Yes.
> 
>> Did you used GPIOD_OUT_HIGH for reset to have the chip out of reset at this
>> point?
> 
> No, ~RESET is an active-low signal.  GPIOD_OUT_LOW should really be
> called GPIOD_OUT_DEASSERTED or something like that.  The code ensures
> that the chip is in RESET and ~ENABLEd after parsing the GPIOs.
> 
>>> +               if (IS_ERR(gpios->reset)) {
>>> +                       dev_err(&spi->dev, "missing reset gpio.\n");
>>> +                       return PTR_ERR(gpios->reset);
>>> +               }
>>> +       } else {
>>> +               gpios->reset = devm_gpiod_get_optional(&spi->dev,
>>> +                                                      "reset", GPIOD_OUT_HIGH);
>>> +       }
>>> +       return 0;
>>> +}
>>> +
>>> +static void wilc_wlan_power(struct wilc *wilc, bool on)
>>> +{
>>> +       struct wilc_spi *spi_priv = wilc->bus_data;
>>> +       struct wilc_gpios *gpios = &spi_priv->gpios;
>>> +
>>> +       if (on) {
>>> +               gpiod_set_value(gpios->enable, 1);      /* assert ENABLE */
>>> +               mdelay(5);
>>> +               gpiod_set_value(gpios->reset, 0);       /* deassert RESET */
>>
>> From what I can tell from gpiolib code, requesting the pin from device tree
>> with:
>>
>> +        reset-gpios = <&pioA 6 GPIO_ACTIVE_LOW>;
>>
>> makes the value written with gpiod_set_value() to be negated, thus the 0
>> written here is translated to a 1 on the pin. Is there a reason you did it
>> like this?
> 
> Yes, of course.  RESET is an active-low signal, as defined in the
> datasheet.

Right, I missed that.

> 
>> Would it have been simpler to have both pins requested with
>> GPIO_ACTIVE_HIGH and here to do gpiod_set_value(gpio, 1) for both of the
>> pin. In this way, at the first read of the code one one would have been
>> telling that it does what datasheet specifies: for power on toggle enable
>> and reset gpios from 0 to 1 with a delay in between.
> 
> I think you're confusing 0 and 1 with low-voltage and high-voltage.  0
> means de-assert the signal, 1 means assert the signal.  Whether that
> translates to a low voltage or a high voltage depends on whether the
> signal a active-low or active-high.
> 
>>
>>
>>> +       } else {
>>> +               gpiod_set_value(gpios->reset, 1);       /* assert RESET */
>>> +               gpiod_set_value(gpios->enable, 0);      /* deassert ENABLE */
>>
>> I don't usually see comments near the code line in kernel. Maybe move them
>> before the actual code line or remove them at all as the code is impler enough?
> 
> You're kidding, right?
> 
>   --david
>