[dpdk-dev] [PATCH] librte_ethdev: extend dpdk api led control to query capability

[Andrew Rybchenko]

On 1/8/20 5:27 PM, Thomas Monjalon wrote:
> 08/01/2020 15:15, Andrew Rybchenko:
>> On 1/8/20 4:52 PM, Ferruh Yigit wrote:
>>> On 1/8/2020 1:25 PM, Thomas Monjalon wrote:
>>>> 08/01/2020 14:20, Ferruh Yigit:
>>>>> On 1/8/2020 1:06 PM, Thomas Monjalon wrote:
>>>>>> 08/01/2020 13:59, Ferruh Yigit:
>>>>>>> But for dev_ops, instead of having another capabilities indicator, which
>>>>>>> requires PMDs to keep this synchronized, I think it is better if we can self
>>>>>>> contain this information within dev_ops, like not implementing dev_ops would
>>>>>>> mean it is not supported, this way it is easier to maintain and less error prone.
>>>>>> It means the dev_ops is resetted at init if a device does not support the feature.
>>>>>> It is against having const dev_ops.
>>>>> I didn't get your comment.
>>>>> For example getting FW version, I am saying instead of keeping another piece of
>>>>> information to say if it is supported by device/driver, better to grasp this
>>>>> from if the driver implemented 'fw_version_get' dev_ops or not.
>>>> I like this approach.
>>>> Capabilities should be expressed by setting the function pointer or not (NULL).
>>>> But a driver may support a feature for a subset of devices.
>>> In that case dev_ops itself can return the '-ENOTSUP', since application
>>> interaction will be through the ethdev API, either API send '-ENOTSUP' because
>>> the dev_ops is NULL or dev_ops itself send the '-ENOTSUP' because of the
>>> underlying version of the device, for application it will be clear that that
>>> feature is not supported.
>> I think it is a good illustration why deriving the capability
>> from dev_ops pointer is not that good idea.
>>
>>>> If a device does not support a feature, the function pointer must be set to NULL.
>>>> The only issue is having dev_ops as a const struct.
>>> Not sure about changing the dev_ops on runtime, it can be very hard to debug.
>> I hope it was just an idea to copy dev_ops and adjust in
>> accordance with the device capabilities on register.
>> I.e. not fully dynamic changes in runtime.
> Changing a function pointer in runtime is tough :)
> I was thinking about changing it during init but I don't really see a great value.

Yes exactly, copying just solve the 'const' problem.

> Probably better to return ENOTSUP.
>
> Anyway it does not address the capability info need.

Yes, I agree. Back to other branch of the thread:
dev_info flag vs dedicated dev_ops function.