On Wed, Apr 5, 2017 at 6:10 PM, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote:
> On 04/05, Rick Altherr wrote:
>> On Wed, Apr 5, 2017 at 1:27 PM, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote:
>> > On 03/23, Rick Altherr wrote:
>> >> +
>> >> +static int aspeed_adc_probe(struct platform_device *pdev)
>> >> +{
>> >> + struct iio_dev *indio_dev;
>> >> + struct aspeed_adc_data *data;
>> >> + const struct aspeed_adc_model_data *model_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)
>> >> + return -ENOMEM;
>> >> +
>> >> + data = iio_priv(indio_dev);
>> >> + data->dev = &pdev->dev;
>> >> +
>> >> + res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> >> + data->base = devm_ioremap_resource(&pdev->dev, res);
>> >> + if (IS_ERR(data->base))
>> >> + return PTR_ERR(data->base);
>> >> +
>> >> + /* 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);
>> >
>> > What if the parent clk is not registered yet? Or if we're not
>> > always using DT in this driver? Put another way, this code is
>> > fragile. But I guess it probably works well enough for now so no
>> > big deal, just pointing out my fear.
>>
>> I'm not terribly worried about not using DT for this driver as it is
>> for an ARM SoC's built-in ADC which is only supported via DT. I take
>> your point though. What's the right way to do this? Use clk_get() to
>> request by name and clock-names in the DT?
>
> Yes that will work. When we add probe defer to clk_get() things
> will work better. Presumably the clocks property already exists
> for this device so that of_clk_get_parent_name() works so it's
> not a binding change?
The bindings include clocks but not clock-names. In this case,
clk_register_divider() only has variants that take a parent clock
name. I can't see what I'd do with the result of clk_get(). If the
bindings provide clock-names, I can provide a fixed string for the
parent name instead of relying on of_clk_get_parent_name(). The
removes an explicit driver dependency on DT. I'm unclear if it
resolves your concerns about registration ordering.
>
>>
>> >
>> >> +
>> >> + data->clk_prescaler = clk_hw_register_divider(
>> >> + &pdev->dev, "prescaler", clk_parent_name, 0,
>> >> + data->base + ASPEED_REG_CLOCK_CONTROL,
>> >> + 17, 15, 0, &data->clk_lock);
>> >> + if (IS_ERR(data->clk_prescaler))
>> >> + return PTR_ERR(data->clk_prescaler);
>> >> +
>> >> + /*
>> >> + * 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_REG_CLOCK_CONTROL,
>> >> + 0, 10, 0, &data->clk_lock);
>> >> + if (IS_ERR(data->clk_scaler)) {
>> >> + ret = PTR_ERR(data->clk_scaler);
>> >> + goto scaler_error;
>> >> + }
>> >> +
>> >> + /* Start all channels in normal mode. */
>> >> + clk_prepare_enable(data->clk_scaler->clk);
>> >
>> > Eventually we'd like to get rid of hw->clk pointer so that users
>> > have to call some sort of clk_get() API and then we get warm
>> > fuzzies from knowing who is consuming a clk structure. Can you
>> > change this to register a clk provider and call clk_get()? I
>> > think a device that references itself should be OK in DT still,
>> > and would properly reflect what's going on.
>>
>> Do you mean call of_clk_add_hw_provider with of_clk_hw_simple_get or
>> something else? I'm still wrapping my head around the distinction
>> between clk, clk_hw, and a clk provider.
>>
>
> Yes. Unless you don't want to expose these details in DT because
> it's all internal to the device?
>
There's no reason to expose the scaler or prescaler in DT. These are
clocks that internal to the ADC and have no way for other devices to
use them. I only used the clock framework to avoid reinventing the
wheel on calculating divider values for a desired clock rate.
> In that case we need to go merge that patch on the clk list to
> have clk_hw_create_clk() or something like that, so we can turn a
> clk_hw structure into a clk pointer without directly referencing
> the clk member of clk_hw.
This makes the most sense to me.
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
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