linux-kernel - Re: [PATCH] iio: adc: aspeed: Deassert reset in probe

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Date:   Mon, 30 Oct 2017 17:21:57 +0100
From:   Philipp Zabel <philipp.zabel@...il.com>
To:     Joel Stanley <joel@....id.au>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Rick Altherr <raltherr@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: adc: aspeed: Deassert reset in probe

Hi Joel,

On Mon, Oct 30, 2017 at 8:22 AM, Joel Stanley <joel@....id.au> wrote:
> The ASPEED SoC must deassert a reset in order to use the ADC peripheral.
>
> The device tree bindings are updated to document the resets phandle, and
> the example is updated to match what is expected for both the reset and
> clock phandle.
>
> Signed-off-by: Joel Stanley <joel@....id.au>
> ---
>  .../devicetree/bindings/iio/adc/aspeed_adc.txt      |  4 +++-
>  drivers/iio/adc/aspeed_adc.c                        | 21 ++++++++++++++++-----
>  2 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/iio/adc/aspeed_adc.txt b/Documentation/devicetree/bindings/iio/adc/aspeed_adc.txt
> index 674e133b7cd7..034fc2ba100e 100644
> --- a/Documentation/devicetree/bindings/iio/adc/aspeed_adc.txt
> +++ b/Documentation/devicetree/bindings/iio/adc/aspeed_adc.txt
> @@ -8,6 +8,7 @@ Required properties:
>  - reg: memory window mapping address and length
>  - clocks: Input clock used to derive the sample clock. Expected to be the
>            SoC's APB clock.
> +- resets: Reset controller phandle

Adding new required properties to existing bindings would break backwards
compatibility. In this case, the reset is optional anyway.

>  - #io-channel-cells: Must be set to <1> to indicate channels are selected
>                       by index.
>
> @@ -15,6 +16,7 @@ Example:
>         adc@...e9000 {
>                 compatible = "aspeed,ast2400-adc";
>                 reg = <0x1e6e9000 0xb0>;
> -               clocks = <&clk_apb>;
> +               clocks = <&syscon ASPEED_CLK_APB>;
> +               resets = <&syscon ASPEED_RESET_ADC>;
>                 #io-channel-cells = <1>;
>         };
> diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c
> index 8a958d5f1905..0fc9712cdde4 100644
> --- a/drivers/iio/adc/aspeed_adc.c
> +++ b/drivers/iio/adc/aspeed_adc.c
> @@ -17,6 +17,7 @@
>  #include <linux/module.h>
>  #include <linux/of_platform.h>
>  #include <linux/platform_device.h>
> +#include <linux/reset.h>
>  #include <linux/spinlock.h>
>  #include <linux/types.h>
>
> @@ -53,11 +54,12 @@ struct aspeed_adc_model_data {
>  };
>
>  struct aspeed_adc_data {
> -       struct device   *dev;
> -       void __iomem    *base;
> -       spinlock_t      clk_lock;
> -       struct clk_hw   *clk_prescaler;
> -       struct clk_hw   *clk_scaler;
> +       struct device           *dev;
> +       void __iomem            *base;
> +       spinlock_t              clk_lock;
> +       struct clk_hw           *clk_prescaler;
> +       struct clk_hw           *clk_scaler;
> +       struct reset_control    *rst;
>  };
>
>  #define ASPEED_CHAN(_idx, _data_reg_addr) {                    \
> @@ -217,6 +219,13 @@ static int aspeed_adc_probe(struct platform_device *pdev)
>                 goto scaler_error;

Since data->rst is initialized to NULL, this does work.
It would be nicer though to add a new label for errors after
reset_control_deassert below.

>         }
>
> +       data->rst = devm_reset_control_get_optional_exclusive(&pdev->dev, NULL);
> +       if (IS_ERR(data->rst)) {
> +               dev_err(&pdev->dev, "invalid reset controller in device tree");
> +               data->rst = NULL;
> +       } else
> +               reset_control_deassert(data->rst);

I'd return an error if devm_reset_control_get_optional_exclusive fails.
Then reset_control_deassert can be called unconditionally:

        data->rst = devm_reset_control_get_optional_exclusive(&pdev->dev, NULL);
        if (IS_ERR(data->rst)) {
                dev_err(&pdev->dev, "invalid reset controller in device tree");
                ret = PTR_ERR(data->rst);
                goto reset_error;
        }
        reset_control_deassert(data->rst);

> +
>         model_data = of_device_get_match_data(&pdev->dev);
>
>         if (model_data->wait_init_sequence) {
> @@ -268,6 +277,7 @@ static int aspeed_adc_probe(struct platform_device *pdev)
>
>  scaler_error:
>         clk_hw_unregister_divider(data->clk_prescaler);
> +       reset_control_assert(data->rst);

This should be done in reverse order, before
clk_hw_unregister_divider, and get its own label.

>         return ret;
>  }
>
> @@ -282,6 +292,7 @@ static int aspeed_adc_remove(struct platform_device *pdev)
>         clk_disable_unprepare(data->clk_scaler->clk);
>         clk_hw_unregister_divider(data->clk_scaler);
>         clk_hw_unregister_divider(data->clk_prescaler);
> +       reset_control_assert(data->rst);

Same here, if the reset is deasserted after registering clk_scaler,
it would be cleaner to assert it before unregistering the clock.

>
>         return 0;
>  }
> --
> 2.14.1
>

regards
Philipp