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

[Ferruh Yigit <ferruh.yigit@intel.com>]

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.

> 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.