On Mon, Apr 24, 2023 at 02:49:29PM +0200, Arnaud POULIQUEN wrote:
> Hello,
>
> On 4/22/23 12:42, Sarannya S wrote:
> > From: Deepak Kumar Singh <quic_deesin@xxxxxxxxxxx>
> >
> > Some transports like Glink support the state notifications between
> > clients using flow control signals similar to serial protocol signals.
> > Local glink client drivers can send and receive flow control status
> > to glink clients running on remote processors.
> >
> > Add APIs to support sending and receiving of flow control status by
> > rpmsg clients.
> >
> > Signed-off-by: Deepak Kumar Singh <quic_deesin@xxxxxxxxxxx>
> > Signed-off-by: Sarannya S <quic_sarannya@xxxxxxxxxxx>
> > ---
> > drivers/rpmsg/rpmsg_core.c | 21 +++++++++++++++++++++
> > drivers/rpmsg/rpmsg_internal.h | 2 ++
> > include/linux/rpmsg.h | 15 +++++++++++++++
> > 3 files changed, 38 insertions(+)
> >
> > diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> > index a2207c0..e8bbe05 100644
> > --- a/drivers/rpmsg/rpmsg_core.c
> > +++ b/drivers/rpmsg/rpmsg_core.c
> > @@ -331,6 +331,25 @@ int rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src, u32 dst,
> > EXPORT_SYMBOL(rpmsg_trysend_offchannel);
> >
> > /**
> > + * rpmsg_set_flow_control() - sets/clears serial flow control signals
> > + * @ept: the rpmsg endpoint
> > + * @enable: pause/resume incoming data flow
> > + * @dst: destination address of the endpoint
> > + *
> > + * Return: 0 on success and an appropriate error value on failure.
> > + */
> > +int rpmsg_set_flow_control(struct rpmsg_endpoint *ept, bool enable, u32 dst)
> > +{
> > + if (WARN_ON(!ept))
> > + return -EINVAL;
> > + if (!ept->ops->set_flow_control)
> > + return -ENXIO;
>
> Here we return an error if the backend does not implement the ops.
> But the set_flow_control ops is optional.
> Should we return 0 instead with a debug message?
>
It seems reasonable to allow the software to react to the absence of
flow control support, so a debug message wouldn't help.
But advertising that more explicitly by returning something like
EOPNOTSUPP seems better.
Regards,
Bjorn
