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

[Laurent Hardy <laurent.hardy@6wind.com>]

Hi all,

On 1/8/20 10:55 AM, David Marchand wrote:
> On Wed, Jan 8, 2020 at 10:09 AM Ferruh Yigit <ferruh.yigit@intel.com> wrote:
>> On 1/8/2020 8:56 AM, David Marchand wrote:
>>> Hello Laurent,
>>>
>>> Bonne année.
>>>
>>> Cc: maintainers.
>>>
>>> On Tue, Jan 7, 2020 at 3:57 PM Laurent Hardy <laurent.hardy@6wind.com> wrote:
>>>> In current led control API we have no way to know if a device is able
>>>> to handle on/off requests coming from the application.
>>>> Knowing if the device is led control capable could be useful to avoid
>>>> exchanges between application and kernel.
>>>> Using the on/off requests to flag if the device is led control capable
>>>> (based on the ENOSUP returned error) is not convenient as such request
>>>> can change the led state on device.
>>>>
>>>> This patch adds a new function rte_eth_led_ctrl_capable() that will look
>>>> for led_off/on dev ops availability on the related pmd, to know if the
>>>> device is able to handle such led control requests (on/off).
>>> This patch breaks the ABI, which is BAD :-).
>> Why it is an ABI break, dev_ops should be between library and drivers, so it
>> should be out of the ABI concern, isn't it.
> You are right.
> So in our context, this is not an ABI breakage.
> But abidiff still reports it, so maybe some filtering is required to
> avoid this false positive.
>
> Note that if we insert an ops before rx_queue_count, we would have a
> real ABI breakage, as this ops is accessed via an inline wrapper by
> applications.
>
>
>>> This new api only needs to look at the existing ops, so you can remove
>>> the (unused in your patch) dev_led_ctrl_capable ops.
>>>
>>> OTOH, would it make sense to expose this capability in dev_flags?
>>>
>> 'rte_eth_led_on()' & 'rte_eth_led_off()' APIs returns '-ENOTSUP' when the not
>> supported, can that help application to understand?
> You might want to know it is supported without changing the state.
> Laurent?

First, happy new year :)

Yes exactly, the purpose of this patch is to query if the device is led 
control capable or not without changing the led state.

About exposing the capability through a dev_flags, means to make some 
modification in each pmds. It looks more easy in term of pmds 
maintenance to relying on the rte_eth_led_off()/on() dev ops 
availability at rte_ethdev level, right ?

>
>
> --
> David Marchand
>
>