linux-kernel - Re: [PATCH v4 2/2] usb: overridable hub bInterval by device node

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Date:   Wed, 4 Dec 2019 15:07:50 +0800
From:   Ikjoon Jang <ikjn@...omium.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     linux-usb@...r.kernel.org,
        GregKroah-Hartman <gregkh@...uxfoundation.org>,
        RobHerring <robh+dt@...nel.org>,
        MarkRutland <mark.rutland@....com>,
        SuwanKim <suwan.kim027@...il.com>,
        "GustavoA . R . Silva" <gustavo@...eddedor.com>,
        JohanHovold <johan@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nicolas Boichat <drinkcat@...omium.org>
Subject: Re: [PATCH v4 2/2] usb: overridable hub bInterval by device node

On Tue, Dec 3, 2019 at 11:23 PM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Tue, 3 Dec 2019, 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.
> >
> > Signed-off-by: Ikjoon Jang <ikjn@...omium.org>
> > Acked-by: Alan Stern <stern@...land.harvard.edu>
> > ---
> >  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))) {
> > +             u32 interval = 0;
>
> Coding style: there should be a blank line here.  Also, you don't need
> the "= 0" initializer.
>
> Otherwise okay.

Okay, I will fix that.
Thank you!

>
> Alan Stern
>
> > +             if (!of_property_read_u32(ddev->of_node, "hub,interval",
> > +                                 &interval))
> > +                     d->bInterval = min_t(u8, interval, 255);
> > +     }
> > +
> >       /*
> >        * Fix up bInterval values outside the legal range.
> >        * Use 10 or 8 ms if no proper value can be guessed.
>