Date:   Wed, 22 Mar 2017 20:17:12 +1030
From:   Joel Stanley <joel@....id.au>
To:     Rick Altherr <raltherr@...gle.com>
Cc:     OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Andreas Klinger <ak@...klinger.de>,
        Rob Herring <robh@...nel.org>, linux-iio@...r.kernel.org,
        Hartmut Knaack <knaack.h@....de>,
        Quentin Schulz <quentin.schulz@...e-electrons.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Marek Vasut <marek.vasut+renesas@...il.com>,
        Matt Ranostay <mranostay@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Crestez Dan Leonard <leonard.crestez@...el.com>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Fabrice Gasnier <fabrice.gasnier@...com>,
        Jonathan Cameron <jic23@...nel.org>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Jacopo Mondi <jacopo@...ndi.org>
Subject: Re: [PATCH v2 2/2] iio: Aspeed AST2400/AST2500 ADC

On Wed, Mar 22, 2017 at 7:18 AM, Rick Altherr <raltherr@...gle.com> wrote:
> Aspeed AST2400/AST2500 BMC SoCs include a 16 channel, 10-bit ADC. Low
> and high threshold interrupts are supported by the hardware but are not
> currently implemented.
>
> Signed-off-by: Rick Altherr <raltherr@...gle.com>

Looks good Rick. I gave it a review from the perspective of the Aspeed
soc. I also gave it a spin on the Aspeed AST2500 EVB which mostly
worked, but uncovered some things that need addressing.

My device tree additions looked like this:

  adc: adc@...e9000 {
          compatible = "aspeed,ast2500-adc";
          reg = <0x1e6e9000 0xb0>;
          clocks = <&clk_apb>;
          #io-channel-cells = <1>;

          pinctrl-names = "default";
          pinctrl-0 = <&pinctrl_adc0_default>;
  };

  iio-hwmon {
          compatible = "iio-hwmon";
          io-channels = <&adc 0>;
  };

I got this output from lm-sensors when booted:

iio_hwmon-isa-0000
Adapter: ISA adapter
in1:          +1.28 V

I then wired up ADC0 to ADC_12V_TW on the EVB. The above changed to:

 iio_hwmon-isa-0000
Adapter: ISA adapter
in1:          +1.80 V

ADC_12V_TW is the 12V rail sampled through a voltage divider. The
voltage should be: 12 * 680 / ( 5600 + 680) = 1.299

cat /sys/bus/iio/devices/iio:device0/in_voltage1_raw
738

738 / 1023 * 1.8 = 1.2975

Looks like the first channel is working! However our reference is
incorrect. Your driver has ASPEED_ADC_REF_VOLTAGE but doesn't use it.
It does hardcode 2500 in the aspeed_adc_read_raw callback:

          case IIO_CHAN_INFO_SCALE:
                  *val = 2500; // mV
                  *val2 = 10;
                  return IIO_VAL_FRACTIONAL_LOG2;

Should this value the the constant you define?

Regardless, I don't think the reference voltage should be a constant.
This is going to vary from system to system. Can we put it in the
device tree? I notice other devices have vref-supply in their
bindings.

I noticed that in_voltage_scale is writable. However, it did not
accept any of the values I give it. Is this because we do not handle
it in aspeed_adc_write_raw?

I suggest we add the reference in the device tree bindings, and also
allow the value to be updated from userspace.

> ---
>
> Changes in v2:
> - Rewritten as an IIO device
> - Renamed register macros to describe the register's purpose
> - Replaced awkward reading of 16-bit data registers with readw()
> - Added Kconfig dependency on COMPILE_TEST
>
>  drivers/iio/adc/Kconfig      |  10 ++
>  drivers/iio/adc/Makefile     |   1 +
>  drivers/iio/adc/aspeed_adc.c | 271 +++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 282 insertions(+)
>  create mode 100644 drivers/iio/adc/aspeed_adc.c
>
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 2268a6fb9865..9672d799a3fb 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -130,6 +130,16 @@ config AD799X
>           To compile this driver as a module, choose M here: the module will be
>           called ad799x.
>
> +config ASPEED_ADC
> +       tristate "Aspeed AST2400/AST2500 ADC"

You could just say Aspeed ADC to save us having to update it when the
ast2600 comes out.

> +       depends on ARCH_ASPEED || COMPILE_TEST
> +       help
> +         If you say yes here you get support for the Aspeed AST2400/AST2500
> +         ADC.
> +
> +         To compile this driver as a module, choose M here: the module will be
> +         called aspeed_adc.

Don't forget to test compiling as a module.


> diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c
> new file mode 100644
> index 000000000000..9220909aefd4
> --- /dev/null

> +#define ASPEED_ADC_NUM_CHANNELS                        16
> +#define ASPEED_ADC_REF_VOLTAGE                 2500 /* millivolts */
> +#define ASPEED_ADC_RESOLUTION_BITS             10
> +#define ASPEED_ADC_MIN_SAMP_RATE               10000
> +#define ASPEED_ADC_MAX_SAMP_RATE               500000
> +#define ASPEED_ADC_CLOCKS_PER_SAMPLE           12
> +
> +#define ASPEED_ADC_REG_ENGINE_CONTROL          0x00
> +#define ASPEED_ADC_REG_INTERRUPT_CONTROL       0x04
> +#define ASPEED_ADC_REG_VGA_DETECT_CONTROL      0x08
> +#define ASPEED_ADC_REG_CLOCK_CONTROL           0x0C
> +#define ASPEED_ADC_REG_MAX                     0xC0
> +
> +#define ASPEED_ADC_OPERATION_MODE_POWER_DOWN   (0x0 << 1)
> +#define ASPEED_ADC_OPERATION_MODE_STANDBY      (0x1 << 1)
> +#define ASPEED_ADC_OPERATION_MODE_NORMAL       (0x7 << 1)
> +
> +#define ASPEED_ADC_ENGINE_ENABLE       BIT(0)

Nit: You could chose to label these with a shorter prefix. Drop the
aspeed or adc, or both.

> +
> +static int aspeed_adc_read_raw(struct iio_dev *indio_dev,
> +                              struct iio_chan_spec const *chan,
> +                              int *val, int *val2, long mask)
> +{
> +       struct aspeed_adc_data *data = iio_priv(indio_dev);
> +
> +       switch (mask) {
> +       case IIO_CHAN_INFO_RAW:
> +               *val = readw(data->base + chan->address);
> +               return IIO_VAL_INT;
> +
> +       case IIO_CHAN_INFO_SCALE:
> +               *val = 2500; // mV
> +               *val2 = 10;

What does 10 mean?

> +               return IIO_VAL_FRACTIONAL_LOG2;
> +
> +       case IIO_CHAN_INFO_SAMP_FREQ:
> +               *val = clk_get_rate(data->clk_scaler->clk) /
> +                               ASPEED_ADC_CLOCKS_PER_SAMPLE;
> +               return IIO_VAL_INT;
> +
> +       default:
> +               return -EINVAL;
> +       }
> +}
> +
> +static int aspeed_adc_write_raw(struct iio_dev *indio_dev,
> +                               struct iio_chan_spec const *chan,
> +                               int val, int val2, long mask)
> +{
> +       struct aspeed_adc_data *data = iio_priv(indio_dev);
> +
> +       switch (mask) {

Handle IIO_CHAN_INFO_SCALE here too.

> +       case IIO_CHAN_INFO_SAMP_FREQ:
> +               if (val < ASPEED_ADC_MIN_SAMP_RATE ||
> +                   val > ASPEED_ADC_MAX_SAMP_RATE)
> +                       return -EINVAL;
> +
> +               clk_set_rate(data->clk_scaler->clk,
> +                               val * ASPEED_ADC_CLOCKS_PER_SAMPLE);
> +               return 0;
> +
> +       default:
> +               return -EINVAL;
> +       }
> +}
> +
> +static int aspeed_adc_reg_access(struct iio_dev *indio_dev,
> +                                unsigned int reg, unsigned int writeval,
> +                                unsigned int *readval)
> +{
> +       struct aspeed_adc_data *data = iio_priv(indio_dev);
> +
> +       if (!readval || reg % 4 || reg > ASPEED_ADC_REG_MAX)
> +               return -EINVAL;
> +
> +       *readval = readl(data->base + reg);
> +       return 0;
> +}
> +
> +static const struct iio_info aspeed_adc_iio_info = {
> +       .driver_module = THIS_MODULE,
> +       .read_raw = &aspeed_adc_read_raw,
> +       .write_raw = &aspeed_adc_write_raw,
> +       .debugfs_reg_access = &aspeed_adc_reg_access,
> +};
> +
> +static int aspeed_adc_probe(struct platform_device *pdev)
> +{
> +       struct iio_dev *indio_dev;
> +       struct aspeed_adc_data *data;
> +       struct resource *res;
> +       const char *clk_parent_name;
> +       int ret;
> +       u32 adc_engine_control_reg_val;
> +
> +       indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*data));
> +       if (!indio_dev) {
> +               dev_err(&pdev->dev, "Failed allocating iio device\n");
> +               return -ENOMEM;
> +       }
> +
> +       data = iio_priv(indio_dev);
> +
> +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +       data->base = devm_ioremap_resource(&pdev->dev, res);
> +       if (IS_ERR(data->base)) {
> +               dev_err(&pdev->dev, "Failed allocating device resources\n");

The function you're calling will do that for you

http://lxr.free-electrons.com/source/lib/devres.c?v=4.10#L134

Just return the error here. I'd consider dropping the dev_errs for the
other cases in the probe. We still get a reasonable error message
without printing something ourselves. For example, when bailing out
with ENOMEM:

[    5.510000] aspeed_adc: probe of 1e6e9000.adc failed with error -12


> +               ret = PTR_ERR(data->base);
> +               goto resource_error;
> +       }
> +
> +       /* Register ADC clock prescaler with source specified by device tree. */
> +       spin_lock_init(&data->clk_lock);
> +       clk_parent_name = of_clk_get_parent_name(pdev->dev.of_node, 0);
> +
> +       data->clk_prescaler = clk_hw_register_divider(
> +                               &pdev->dev, "prescaler", clk_parent_name, 0,
> +                               data->base + ASPEED_ADC_REG_CLOCK_CONTROL,
> +                               17, 15, 0, &data->clk_lock);

I couldn't see any other drivers that use these functions outside of
drivers/clk. I like what you've done here, but someone who understands
the clock framework should take a look.


> +       if (IS_ERR(data->clk_prescaler)) {
> +               dev_err(&pdev->dev, "Failed allocating prescaler clock\n");
> +               ret = PTR_ERR(data->clk_prescaler);
> +               goto prescaler_error;
> +       }
> +
> +       /*
> +        * Register ADC clock scaler downstream from the prescaler. Allow rate
> +        * setting to adjust the prescaler as well.
> +        */
> +       data->clk_scaler = clk_hw_register_divider(
> +                               &pdev->dev, "scaler", "prescaler",
> +                               CLK_SET_RATE_PARENT,
> +                               data->base + ASPEED_ADC_REG_CLOCK_CONTROL,
> +                               0, 10, 0, &data->clk_lock);
> +       if (IS_ERR(data->clk_scaler)) {
> +               dev_err(&pdev->dev, "Failed allocating scaler clock\n");
> +               ret = PTR_ERR(data->clk_scaler);
> +               goto scaler_error;
> +       }
> +
> +       /* Start all channels in normal mode. */
> +       clk_prepare_enable(data->clk_scaler->clk);
> +       adc_engine_control_reg_val = GENMASK(31, 16) |
> +               ASPEED_ADC_OPERATION_MODE_NORMAL | ASPEED_ADC_ENGINE_ENABLE;
> +       writel(adc_engine_control_reg_val,
> +               data->base + ASPEED_ADC_REG_ENGINE_CONTROL);
> +
> +       indio_dev->name = dev_name(&pdev->dev);
> +       indio_dev->dev.parent = &pdev->dev;
> +       indio_dev->info = &aspeed_adc_iio_info;
> +       indio_dev->modes = INDIO_DIRECT_MODE;
> +       indio_dev->channels = aspeed_adc_iio_channels;
> +       indio_dev->num_channels = ARRAY_SIZE(aspeed_adc_iio_channels);

Should we be able to enable just the channels that we want? Perhaps
only the ones that are requested through the device tree?

> +
> +       ret = iio_device_register(indio_dev);
> +       if (ret) {
> +               dev_err(&pdev->dev, "Could't register the device.\n");
> +               goto iio_register_error;
> +       }
> +
> +       return 0;
> +
> +iio_register_error:
> +       writel(0x0, data->base + ASPEED_ADC_REG_ENGINE_CONTROL);

Should this be done in remove as well?

> +       clk_disable_unprepare(data->clk_scaler->clk);
> +       clk_hw_unregister_divider(data->clk_scaler);
> +
> +scaler_error:
> +       clk_hw_unregister_divider(data->clk_prescaler);
> +
> +prescaler_error:
> +resource_error:
> +       return ret;

You could just return from the error where it happens in the case
where no cleanup is required.

> +}
> +
> +static int aspeed_adc_remove(struct platform_device *pdev)
> +{
> +       struct iio_dev *indio_dev = platform_get_drvdata(pdev);
> +       struct aspeed_adc_data *data = iio_priv(indio_dev);
> +
> +       iio_device_unregister(indio_dev);
> +       clk_disable_unprepare(data->clk_scaler->clk);
> +       clk_hw_unregister_divider(data->clk_scaler);
> +       clk_hw_unregister_divider(data->clk_prescaler);
> +
> +       return 0;
> +}
> +
> +const struct of_device_id aspeed_adc_matches[] = {
> +       { .compatible = "aspeed,ast2400-adc" },
> +       { .compatible = "aspeed,ast2500-adc" },
> +};

This is missing a null entry to terminate.

> +MODULE_DEVICE_TABLE(of, aspeed_adc_matches);
> +
> +static struct platform_driver aspeed_adc_driver = {
> +       .probe = aspeed_adc_probe,
> +       .remove = aspeed_adc_remove,
> +       .driver = {
> +               .name = KBUILD_MODNAME,
> +               .of_match_table = aspeed_adc_matches,
> +       }
> +};
> +
> +module_platform_driver(aspeed_adc_driver);
> +
> +MODULE_AUTHOR("Rick Altherr <raltherr@...gle.com>");
> +MODULE_DESCRIPTION("Aspeed AST2400/2500 ADC Driver");
> +MODULE_LICENSE("GPL");
> --
> 2.12.1.500.gab5fba24ee-goog
>

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