[PATCH v2] i2c: designware: add reset interface

[zhangfei]

On 2016年12月23日 18:26, Philipp Zabel wrote:
> Hi Zhangfei,
>
> Am Freitag, den 16.12.2016, 11:01 +0800 schrieb zhangfei:
>> Hi, Philipp
>>
>> On 2016年12月16日 10:45, zhangfei wrote:
> [...]
>> Sorry, a bit confused.
>> Is that mean we should not use devm_reset_control_get_optional()
>> While driver should decide whether use
>> devm_reset_control_get_optional_exclusive() or
>> devm_reset_control_get_optional_shared()
>> What if different platform has different requirement?
>>
>> Looks the difference between _exclusive and _shared is refcount,
>> How about handle this inside, and not decided by interface?
> Because there is a significant difference in how the actual reset line
> behaves. The shared resets are clock-like, and should only be used if
> the device needs them to be deasserted to be enabled, but is fine if
> they have been deasserted earlier or if they are not immediately
> asserted after the device is disabled, but some time later.
> For the shared / non-exclusive resets calling reset_control_assert and
> then reset_control_deassert is not guaranteed to do anything at all,
> because another user of the reset line could keep it deasserted.
>
> If the device needs a reset to be issued at a certain point in time on
> the other hand, for example to reset its state machine or registers to a
> known good state, calling assert must guarantee to actually assert the
> reset. This can only be done if the reset is exclusive.
>
> Whether guaranteed asserts (exclusive reset lines) are necessary depends
> on the device, so this decision has to be made in the driver.

Thanks Philipp for the kind explanation.
Will use devm_reset_control_get_optional_exclusive here.

Thanks