On Wed, Dec 4, 2019 at 12:52 AM Johan Hovold <johan@xxxxxxxxxx> wrote:
>
> On Tue, Dec 03, 2019 at 06:15:52PM +0800, Ikjoon Jang wrote:
> > This patch enables hub device to override its own endpoint descriptor's
> > bInterval when the hub has a device node with "hub,interval" property.
> >
> > When we know reducing autosuspend delay for built-in HIDs is better for
> > power saving, we can reduce it to the optimal value. But if a parent hub
> > has a long bInterval, mouse lags a lot from more frequent autosuspend.
> > So this enables overriding bInterval for a hard wired hub device only
> > when we know that reduces the power consumption.
>
> I think I saw you argue about why this shouldn't simply be configured at
> runtime. Please include that here too, I can't seem to remember why...
Okay.
>
> > Signed-off-by: Ikjoon Jang <ikjn@xxxxxxxxxxxx>
> > Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/usb/core/config.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
> > index 5f40117e68e7..95ec5af42a1c 100644
> > --- a/drivers/usb/core/config.c
> > +++ b/drivers/usb/core/config.c
> > @@ -6,6 +6,7 @@
> > #include <linux/usb.h>
> > #include <linux/usb/ch9.h>
> > #include <linux/usb/hcd.h>
> > +#include <linux/usb/of.h>
> > #include <linux/usb/quirks.h>
> > #include <linux/module.h>
> > #include <linux/slab.h>
> > @@ -257,6 +258,14 @@ static int usb_parse_endpoint(struct device *ddev, int cfgno, int inum,
> > memcpy(&endpoint->desc, d, n);
> > INIT_LIST_HEAD(&endpoint->urb_list);
> >
> > + /* device node property overrides bInterval */
> > + if (usb_of_has_combined_node(to_usb_device(ddev))) {
>
> Not only hubs have combined nodes so you probably need to check
> bDeviceClass here instead.
yes, you're right, I didn't think of that case:
if (to_usb_device(ddev)->descriptor.bDeviceClass == USB_CLASS_HUB &&
ddev->of_node && !of_property_read_u32(...))
Or is it better to check bInterfaceClass, for composite devices with a
hub interface inside?
if (ifp->desc.bInterfaceClass == USB_CLASS_HUB && ddev->of_node &&
!of_property_read_u32(...))
I think checking bInterfaceClass is better.
>
> > + u32 interval = 0;
> > + if (!of_property_read_u32(ddev->of_node, "hub,interval",
> > + &interval))
> > + d->bInterval = min_t(u8, interval, 255);
>
> You want min_t(u32, ...) here to avoid surprises when someone specifies
> a value > 255.
yes, thanks.
>
> > + }
> > +
> > /*
> > * Fix up bInterval values outside the legal range.
> > * Use 10 or 8 ms if no proper value can be guessed.
>
> Johan
I will send v5 soon, thank you.
