Re: [PATCH RFC v6 3/9] PM / devfreq: imx: Register interconnect device

[Chanwoo Choi <cw00.choi@samsung.com>]

On 12/19/19 2:13 AM, Leonard Crestez wrote:
> On 18.12.2019 13:06, Chanwoo Choi wrote:
>> 2019년 12월 18일 (수) 오후 7:14, Leonard Crestez <leonard.crestez@nxp.com>님이 작성:
>>> On 17.12.2019 02:55, Chanwoo Choi wrote:
>>>> On 12/17/19 12:00 AM, Leonard Crestez wrote:
>>>>> On 13.12.2019 06:22, Chanwoo Choi wrote:
>>>>>> On 11/15/19 5:09 AM, Leonard Crestez wrote:
>>>>>>> There is no single device which can represent the imx interconnect.
>>>>>>> Instead of adding a virtual one just make the main &noc act as the
>>>>>>> global interconnect provider.
>>>>>>>
>>>>>>> The imx interconnect provider driver will scale the NOC and DDRC based
>>>>>>> on bandwidth request. More scalable nodes can be added in the future,
>>>>>>> for example for audio/display/vpu/gpu NICs.
>>>>>>>
>>>>>>> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
>>>>>>> ---
>>>>>>>     drivers/devfreq/imx-devfreq.c | 37 +++++++++++++++++++++++++++++++++++
>>>>>>>     1 file changed, 37 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/devfreq/imx-devfreq.c b/drivers/devfreq/imx-devfreq.c
>>>>>>> index 620b344e87aa..585d340c0f6e 100644
>>>>>>> --- a/drivers/devfreq/imx-devfreq.c
>>>>>>> +++ b/drivers/devfreq/imx-devfreq.c
>>>>>>> @@ -15,10 +15,11 @@
>>>>>>>     struct imx_devfreq {
>>>>>>>             struct devfreq_dev_profile profile;
>>>>>>>             struct devfreq *devfreq;
>>>>>>>             struct clk *clk;
>>>>>>>             struct devfreq_passive_data passive_data;
>>>>>>> +  struct platform_device *icc_pdev;
>>>>>>>     };
>>>>>>>
>>>>>>>     static int imx_devfreq_target(struct device *dev,
>>>>>>>                                   unsigned long *freq, u32 flags)
>>>>>>>     {
>>>>>>> @@ -60,11 +61,40 @@ static int imx_devfreq_get_dev_status(struct device *dev,
>>>>>>>             return 0;
>>>>>>>     }
>>>>>>>
>>>>>>>     static void imx_devfreq_exit(struct device *dev)
>>>>>>>     {
>>>>>>> +  struct imx_devfreq *priv = dev_get_drvdata(dev);
>>>>>>> +
>>>>>>>             dev_pm_opp_of_remove_table(dev);
>>>>>>> +  platform_device_unregister(priv->icc_pdev);
>>>>>>> +}
>>>>>>> +
>>>>>>> +/* imx_devfreq_init_icc() - register matching icc provider if required */
>>>>>>> +static int imx_devfreq_init_icc(struct device *dev)
>>>>>>> +{
>>>>>>> +  struct imx_devfreq *priv = dev_get_drvdata(dev);
>>>>>>> +  const char *icc_driver_name;
>>>>>>> +
>>>>>>> +  if (!IS_ENABLED(CONFIG_INTERCONNECT_IMX))
>>>>>>> +          return 0;
>>>>>>
>>>>>> It is not proper to check the enable state of CONFIG_INTERCONNECT_IMX configuration
>>>>>> on device driver. Why don't you add the 'select CONFIG_INTERCONNECT_IMX' on Kconfig?
>>>>>
>>>>> Because it's optional.
>>>>>
>>>>> You can disable interconnect support and just tweak frequencies using
>>>>> the devfreq sysfs API. But indeed would only really be useful for debugging.
>>>>
>>>> Even if it's optional, I don't prefer to use 'IS_ENABLED' macro.
>>>>
>>>> Generally, add or delete the property or value at DT file
>>>> to either enable or disable the some feature provided by device driver
>>>> instead of checking the configuration.
>>>>
>>>> If user adds the property/value related to interconnect
>>>> and imx-bus.c configuration is enabled, the behavior
>>>> related to interconnect on imx-bus.c doesn't work. It make some confusion.
>>>
>>> Maybe I could print a warning if #interconnect-cells is present but
>>> CONFIG_INTERCONNECT_IMX is off?
>>
>> Actually, user might think that if imx-bus.c is enabled
>> , CONFIG_INTERCONNECT_MIX is enabled.
>> Because, the dt binding document of imx-bus.c will
>> contain the property for interconnect.
>>
>> If device driver support the various feature,
>> the device driver have to enable all configuration
>> in order to support the features for user.
> 
> 
>>> An explicit select in Kconfig seems like a pointless limitation but in
>>> practice it would almost never be useful to build one without the other.
>>
>> This patch is for the some CONFIG_INTERCONNECT_IMX driver.
>> I don't understand why is not meaningful to select CONFIG_INTERCONNECT_IMX
>> in Kconfig?
> 
> One issue is that the interconnect graph is described per-soc and there 
> are per-soc config options while imx-bus applies to all. So the "if" 
> condition is not sufficient either; if the per-soc interconnect driver 
> is omitted then the platform device will be added but no driver will be 
> ever be found.
> 
> There are ways around this: for example all of imx interconnect could be 
> built as a single module. But I think it's reasonable for devices to be 
> partially functional if some config options are missing and heavy config 
> customization sometimes requires a bit of debugging.
> 
> There are various issues when building the current series as "m" but I 
> can solve them and post a final patch which sets all the relevant 
> options on "m" in arm64 defconfig. The it will all "just work" out of 
> the box.

Sorry. Actually, I don't understand the relationship perfectly
between imx-bus and imx-interconnect. As you mentioned, I'll
expect the your solution on next version.

> 
>>>> The imx-bus.c have to add the 'select CONFIG_INTERCONNECT_IMX'
>>>> and hand over the right which use the interconnect feature or not, to user.
>>>>
>>>> If there are any requirement to add the additional property
>>>> to check whether interconnect feature will be used or not,
>>>> you can add the extra property. But, I think that it is enough
>>>> to check the '#interconnect-cells'.
>>>>
>>>> In result, I think that it is right to decide the usage of feature
>>>> of device driver by user on Devicetree.
>>>>
>>>>>
>>>>>>> +  if (!of_get_property(dev->of_node, "#interconnect-cells", 0))
>>>>>>> +          return 0;
>>>>>>> +
>>>>>>> +  icc_driver_name = of_device_get_match_data(dev);
>>>>>>> +  if (!icc_driver_name)
>>>>>>> +          return 0;
>>>>>>> +
>>>>>>> +  priv->icc_pdev = platform_device_register_data(
>>>>>>> +                  dev, icc_driver_name, 0, NULL, 0);
>>>>>>> +  if (IS_ERR(priv->icc_pdev)) {
>>>>>>> +          dev_err(dev, "failed to register icc provider %s: %ld\n",
>>>>>>> +                          icc_driver_name, PTR_ERR(priv->devfreq));
>>>>>>> +          return PTR_ERR(priv->devfreq);
>>>>>>> +  }
>>>>>>> +
>>>>>>> +  return 0;
>>>>>>>     }
>>>>>>>
>>>>>>>     static int imx_devfreq_probe(struct platform_device *pdev)
>>>>>>>     {
>>>>>>>             struct device *dev = &pdev->dev;
>>>>>>> @@ -120,18 +150,25 @@ static int imx_devfreq_probe(struct platform_device *pdev)
>>>>>>>                     ret = PTR_ERR(priv->devfreq);
>>>>>>>                     dev_err(dev, "failed to add devfreq device: %d\n", ret);
>>>>>>>                     goto err;
>>>>>>>             }
>>>>>>>
>>>>>>> +  ret = imx_devfreq_init_icc(dev);
>>>>>>> +  if (ret)
>>>>>>> +          goto err;
>>>>>>> +
>>>>>>>             return 0;
>>>>>>>
>>>>>>>     err:
>>>>>>>             dev_pm_opp_of_remove_table(dev);
>>>>>>>             return ret;
>>>>>>>     }
>>>>>>>
>>>>>>>     static const struct of_device_id imx_devfreq_of_match[] = {
>>>>>>> +  { .compatible = "fsl,imx8mq-noc", .data = "imx8mq-interconnect", },
>>>>>>> +  { .compatible = "fsl,imx8mm-noc", .data = "imx8mm-interconnect", },
>>>>>>> +  { .compatible = "fsl,imx8mn-noc", .data = "imx8mn-interconnect", },
>>>>>>>             { .compatible = "fsl,imx8m-noc", },
>>>>>>>             { .compatible = "fsl,imx8m-nic", },
>>>>>>>             { /* sentinel */ },
>>>>>>>     };
>>>>>>>     MODULE_DEVICE_TABLE(of, imx_devfreq_of_match);


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics