Re: [PATCH v20 06/41] usb: host: xhci-sideband: Expose a sideband interrupter enable API

[Wesley Cheng <quic_wcheng@xxxxxxxxxxx>]

Hi Mathias,

On 5/2/2024 4:07 AM, Mathias Nyman wrote:
> On 26.4.2024 0.50, Wesley Cheng wrote:
> > Some use cases maybe require that the secondary interrupter's events to
> > be handled by the OS.  In this case, configure the IMOD and the
> > skip_events property to enable the interrupter's events.  By default,
> > assume that the secondary interrupter doesn't want to enable OS event
> > handling.
> >
> > Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
> > ---
> >   drivers/usb/host/xhci-sideband.c  | 28 ++++++++++++++++++++++++++++
> >   include/linux/usb/xhci-sideband.h |  2 ++
> >   2 files changed, 30 insertions(+)
> >
> > diff --git a/drivers/usb/host/xhci-sideband.c 
> > b/drivers/usb/host/xhci-sideband.c
> > index 255feae33c6e..6fdae9840c11 100644
> > --- a/drivers/usb/host/xhci-sideband.c
> > +++ b/drivers/usb/host/xhci-sideband.c
> > @@ -237,6 +237,30 @@ xhci_sideband_get_event_buffer(struct 
> > xhci_sideband *sb)
> >   }
> >   EXPORT_SYMBOL_GPL(xhci_sideband_get_event_buffer);
> > +/**
> > + * xhci_sideband_enable_interrupt - enable interrupt for secondary 
> > interrupter
> > + * @sb: sideband instance for this usb device
> > + * @imod_interval: number of event ring segments to allocate
> > + *
> > + * Enables OS owned event handling for a particular interrupter if 
> > client
> > + * requests for it.  In addition, set the IMOD interval for this 
> > particular
> > + * interrupter.
> > + *
> > + * Returns 0 on success, negative error otherwise
> > + */
> > +int xhci_sideband_enable_interrupt(struct xhci_sideband *sb, u32 
> > imod_interval)
> > +{
> > +    if (!sb || !sb->ir)
> > +        return -ENODEV;
> > +
> > +    xhci_set_interrupter_moderation(sb->ir, imod_interval);
>
> Is there a need to adjust the moderation after initial setup?
>
> If not then maybe we could pass the imod_interval as a parameter to
> xhci_create_secondary_interrupter(), and avoid exporting
> xhci_set_interrupter_moderation()

Let me preface my comments by saying that I was trying to include some 
aspects of enabling the secondary interrupter line within the main apps 
proc.  If this gets too confusing, I can remove these mechanisms for 
now.  For example, as you mentioned below 
xhci_sideband_enable_interrupt() isn't going to be used in the offload path.

However, I decided to add it so we can have some corresponding function 
that will utilize/set skip_events = false. (as it is "true" by default) 
Again, I can remove this part and revisit later when we actually have a 
use case to handle secondary interrupts on apps.

As for the IMOD setting, depending on what you think, I can add it as 
part of xhci_create_secondary_interrupter()

> > +    sb->ir->skip_events = false;
> > +    xhci_enable_interrupter(sb->ir);
> > +
> > +    return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(xhci_sideband_enable_interrupt);
>
> I can't find the place where xhci_sideband_enable_interrupt() is called in
> this series. How is it planned to be used?
>
> Thanks
> Mathias

Thanks
Wesley Cheng