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

[Andrew Rybchenko <arybchenko@solarflare.com>]

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.