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

[Thomas Monjalon <thomas@monjalon.net>]

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.
Probably better to return ENOTSUP.

Anyway it does not address the capability info need.