linux-kernel - drivers: usb: musb: question about missing break in switch

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Date:   Thu, 09 Feb 2017 02:37:34 -0600
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     b-liu@...com, Greg KH <greg@...ah.com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Senna Tschudin <peter.senna@...il.com>
Subject: drivers: usb: musb: question about missing break in switch

Hello everybody,

I ran into the following piece of code at  
drivers/usb/musb/musb_core.c:1854 (linux-next)

1854/*
1855 * Check the musb devctl session bit to determine if we want to
1856 * allow PM runtime for the device. In general, we want to keep things
1857 * active when the session bit is set except after host disconnect.
1858 *
1859 * Only called from musb_irq_work. If this ever needs to get called
1860 * elsewhere, proper locking must be implemented for musb->session.
1861 */
1862static void musb_pm_runtime_check_session(struct musb *musb)
1863{
1864        u8 devctl, s;
1865        int error;
1866
1867        devctl = musb_readb(musb->mregs, MUSB_DEVCTL);
1868
1869        /* Handle session status quirks first */
1870        s = MUSB_DEVCTL_FSDEV | MUSB_DEVCTL_LSDEV |
1871                MUSB_DEVCTL_HR;
1872        switch (devctl & ~s) {
1873        case MUSB_QUIRK_B_INVALID_VBUS_91:
1874                if (musb->quirk_retries--) {
1875                        musb_dbg(musb,
1876                                 "Poll devctl on invalid vbus,  
assume no session");
1877                        schedule_delayed_work(&musb->irq_work,
1878                                              msecs_to_jiffies(1000));
1879
1880                        return;
1881                }
1882        case MUSB_QUIRK_A_DISCONNECT_19:
1883                if (musb->quirk_retries--) {
1884                        musb_dbg(musb,
1885                                 "Poll devctl on possible host  
mode disconnect");
1886                        schedule_delayed_work(&musb->irq_work,
1887                                              msecs_to_jiffies(1000));
1888
1889                        return;
1890                }
1891                if (!musb->session)
1892                        break;
1893                musb_dbg(musb, "Allow PM on possible host mode  
disconnect");
1894                pm_runtime_mark_last_busy(musb->controller);
1895                pm_runtime_put_autosuspend(musb->controller);
1896                musb->session = false;
1897                return;
1898        default:
1899                break;
1900        }
1901
1902        /* No need to do anything if session has not changed */
1903        s = devctl & MUSB_DEVCTL_SESSION;
1904        if (s == musb->session)
1905                return;
1906
1907        /* Block PM or allow PM? */
1908        if (s) {
1909                musb_dbg(musb, "Block PM on active session: %02x",  
devctl);
1910                error = pm_runtime_get_sync(musb->controller);
1911                if (error < 0)
1912                        dev_err(musb->controller, "Could not  
enable: %i\n",
1913                                error);
1914                musb->quirk_retries = 3;
1915        } else {
1916                musb_dbg(musb, "Allow PM with no session: %02x", devctl);
1917                pm_runtime_mark_last_busy(musb->controller);
1918                pm_runtime_put_autosuspend(musb->controller);
1919        }
1920
1921        musb->session = s;
1922}

The thing is that the case for MUSB_QUIRK_B_INVALID_VBUS_91 is not  
terminated by a break statement, and it falls through to the next case  
MUSB_QUIRK_A_DISCONNECT_19, in case "if (musb->quirk_retries--)" turns  
to be false.

My question here is if this code is intentional?

In case it is not, I will write a patch to fix this, but first it  
would be great to hear any comment about it.

Thank you
--
Gustavo A. R. Silva