On Fri, Oct 28, 2016 at 01:30:07PM +0300, Felipe Balbi wrote:
> Mark Rutland <mark.rutland@xxxxxxx> writes:
> > On Thu, Oct 27, 2016 at 02:08:25PM -0700, John Youn wrote:
> >> On 10/26/2016 3:57 AM, Mark Rutland wrote:
> >> > On Tue, Oct 25, 2016 at 12:42:46PM -0700, John Youn wrote:
> >> >> Add interrupt moderation interval binding for dwc3.
> >
> >> >> + - snps,imod_interval: the interrupt moderation interval.
> >> This series implements the feature and enables it as a workaround for
> >> a particular version of the controller.
> >
> > ... as a workaround for *what*? Is there a bug in that IP version, or an
>
> you didn't receive the entire series, I guess. Here's last patch in the
> series:
No, I did not. Thanks for forwarding this.
> This is a workaround for STAR 9000961433 which affects only version
> 3.00a of the DWC_usb3 core. This prevents the controller interrupt from
> being masked while handling events. Enabling interrupt moderation allows
> us to work around this issue because once the GEVNTCOUNT.count is
> written the IRQ is immediately deasserted and won't be asserted again
> until GEVNTCOUNT.EHB is cleared.
>
> Signed-off-by: John Youn <johnyoun@xxxxxxxxxxxx>
> ---
> drivers/usb/dwc3/core.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 6733838..7fa0832 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -1050,6 +1050,18 @@ static void dwc3_check_params(struct dwc3 *dwc)
> dwc->imod_interval = 0;
> }
>
> + /*
> + * Workaround for STAR 9000961433 which affects only version
> + * 3.00a of the DWC_usb3 core. This prevents the controller
> + * interrupt from being masked while handling events. IMOD
> + * allows us to work around this issue. Enable it for the
> + * affected version.
> + */
> + if (!dwc->imod_interval &&
> + (dwc->revision == DWC3_REVISION_300A)) {
> + dwc->imod_interval = 1;
> + }
> +
> /* Check the maximum_speed parameter */
> switch (dwc->maximum_speed) {
> case USB_SPEED_LOW:
>
> > integration issue? Does the problem vary per-board?
> >
> > Generally, if there's a problem that needs to be worked around, we
> > describe the problem in the DT (perhaps implicitly in the compatible
> > string), and then the kernel chooses the workaround.
>
> Regardless of the silicon erratum, interrupt moderation is a *feature*
> of the IP, common to all instances since revision v3.00a (IIRC). John is
> just using interrupt moderation in the context of implementing this
> workaround. But the actual feature is valid also without the erratum.
Sure, I understand this.
> Another thing to remember is that different applications (i.e. boards)
> might want to moderate the interrupt for different periods. That's,
> again, not related to the erratum at all.
... again, the question is *why*?
If this varies per use-case, then it would be better to handle this
dynamically -- people can run wildly different use-cases on the same
hardware.
I'm not sure that it makes sense for this to be in the DT, though I may
have misunderstood.
Thanks,
Mark.
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