[PATCH v2] i2c: designware: add reset interface

[Jarkko Nikula]

On 12/15/2016 04:11 PM, Phil Reid wrote:
> On 15/12/2016 20:33, Andy Shevchenko wrote:
>> On Thu, 2016-12-15 at 16:59 +0800, Zhangfei Gao wrote:
>>> Some platforms like hi3660 need do reset first to allow accessing
>>> registers
>>
>> Patch itself looks good, but would be nice to have it tested.
>>
>> Reviewed-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
>>
>>>
>>> Signed-off-by: Zhangfei Gao <zhangfei.gao at linaro.org>
>>> ---
>>>  drivers/i2c/busses/i2c-designware-core.h    |  1 +
>>>  drivers/i2c/busses/i2c-designware-platdrv.c | 28
>>> ++++++++++++++++++++++++----
>>>  2 files changed, 25 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/i2c/busses/i2c-designware-core.h
>>> b/drivers/i2c/busses/i2c-designware-core.h
>>> index 0d44d2a..94b14fa 100644
>>> --- a/drivers/i2c/busses/i2c-designware-core.h
>>> +++ b/drivers/i2c/busses/i2c-designware-core.h
>>> @@ -80,6 +80,7 @@ struct dw_i2c_dev {
>>>      void __iomem        *base;
>>>      struct completion    cmd_complete;
>>>      struct clk        *clk;
>>> +    struct reset_control    *rst;
>>>      u32            (*get_clk_rate_khz) (struct
>>> dw_i2c_dev *dev);
>>>      struct dw_pci_controller *controller;
>>>      int            cmd_err;
>>> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c
>>> b/drivers/i2c/busses/i2c-designware-platdrv.c
>>> index 0b42a12..e9016ae 100644
>>> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
>>> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
>>> @@ -38,6 +38,7 @@
>>>  #include <linux/pm_runtime.h>
>>>  #include <linux/property.h>
>>>  #include <linux/io.h>
>>> +#include <linux/reset.h>
>>>  #include <linux/slab.h>
>>>  #include <linux/acpi.h>
>>>  #include <linux/platform_data/i2c-designware.h>
>>> @@ -176,6 +177,14 @@ static int dw_i2c_plat_probe(struct
>>> platform_device *pdev)
>>>      dev->irq = irq;
>>>      platform_set_drvdata(pdev, dev);
>>>
>>> +    dev->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
>>> +    if (IS_ERR(dev->rst)) {
>>> +        if (PTR_ERR(dev->rst) == -EPROBE_DEFER)
>>> +            return -EPROBE_DEFER;
>>> +    } else {
>>> +        reset_control_deassert(dev->rst);
>>> +    }
>>> +
> More for my education. But some drivers seem to handle the error codes a
> little more explicitly.
> Whats the best approach?
>
> eg: From usb/dwc2 driver it continues only if ENOENT / ENOTSUPP errors
> are return
> and ENOMEM / EINVAL etc is a fatal error.
>
> hsotg->reset = devm_reset_control_get_optional(hsotg->dev, "dwc2");
> if (IS_ERR(hsotg->reset)) {
>         ret = PTR_ERR(hsotg->reset);
>         switch (ret) {
>         case -ENOENT:
>         case -ENOTSUPP:
>                 hsotg->reset = NULL;
>                 break;
>         default:
>                 dev_err(hsotg->dev, "error getting reset control %d\n",
>                         ret);
>                 return ret;
>         }

This looks a bit extreme. At least we shouldn't spam log on machines 
that don't need reset control. I kind of think it's good enough to do 
like the patch does. I.e. handle only EPROBE_DEFER and let all other 
errors fall through and keep the controller in reset and let the 
dev->rst carry an error code.

I guess EINVAL is likely seen by developer only. ENOMEM is so fatal that 
things are already falling apart somewhere else too and I don't think it 
needs special handling here.

-- 
Jarkko