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    SubjectRe: dvb usb issues since kernel 4.9
    On Mon, 8 Jan 2018, Linus Torvalds wrote:

    > Can somebody tell which softirq it is that dvb/usb cares about?

    I don't know about the DVB part. The USB part is a little difficult to
    analyze, mostly because the bug reports I've seen are mostly from
    people running non-vanilla kernels. For example, Josef is using a
    Raspberry Pi 3B with a non-standard USB host controller driver:
    dwc_otg_hcd is built into raspbian in place of the normal dwc2_hsotg
    driver.

    Both dwc2_hsotg and ehci-hcd use the tasklets embedded in the
    giveback_urb_bh member of struct usb_hcd. See usb_hcd_giveback_urb()
    in drivers/usb/core/hcd.c; the calls are

    else if (high_prio_bh)
    tasklet_hi_schedule(&bh->bh);
    else
    tasklet_schedule(&bh->bh);

    As it turns out, high_prio_bh gets set for interrupt and isochronous
    URBs but not for bulk and control URBs. The DVB driver in question
    uses bulk transfers.

    xhci-hcd, on the other hand, does not use these tasklets (it doesn't
    set the HCD_BH bit in the hc_driver's .flags member).

    Alan Stern

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