4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chen-Yu Tsai <w...@csie.org>

commit 919ab2524c52e5f801d8873f09145ce822cdd43a upstream.

The musb driver calls into this phy driver to disable/enable squelch
detection. This function was introduced in 24fe86a617c5 ("phy: sun4i-usb:
Add a sunxi specific function for setting squelch-detect"). This
function in turn calls sun4i_usb_phy_write, which uses a mutex to
guard the common access register. Unfortunately musb does this
in atomic context, which results in the following warning with lock
debugging enabled:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
in_atomic(): 1, irqs_disabled(): 128, pid: 96, name: kworker/0:2
CPU: 0 PID: 96 Comm: kworker/0:2 Not tainted 4.8.0-rc4-00181-gd502f8ad1c3e #13
Hardware name: Allwinner sun8i Family
Workqueue: events musb_deassert_reset
[<c010bc01>] (unwind_backtrace) from [<c0109237>] (show_stack+0xb/0xc)
[<c0109237>] (show_stack) from [<c02a669b>] (dump_stack+0x67/0x74)
[<c02a669b>] (dump_stack) from [<c05d68c9>] (mutex_lock+0x15/0x2c)
[<c05d68c9>] (mutex_lock) from [<c02c3589>] (sun4i_usb_phy_write+0x39/0xec)
[<c02c3589>] (sun4i_usb_phy_write) from [<c03e6327>] 
(musb_port_reset+0xfb/0x184)
[<c03e6327>] (musb_port_reset) from [<c03e4917>] (musb_deassert_reset+0x1f/0x2c)
[<c03e4917>] (musb_deassert_reset) from [<c012ecb5>] 
(process_one_work+0x129/0x2b8)
[<c012ecb5>] (process_one_work) from [<c012f5e3>] (worker_thread+0xf3/0x424)
[<c012f5e3>] (worker_thread) from [<c0132dbd>] (kthread+0xa1/0xb8)
[<c0132dbd>] (kthread) from [<c0105f31>] (ret_from_fork+0x11/0x20)

Since the register access is mmio, we can use a spinlock to guard this
specific access, rather than the mutex that guards the entire phy.

Fixes: ba4bdc9e1dc0 ("PHY: sunxi: Add driver for sunxi usb phy")
Cc: Hans de Goede <hdego...@redhat.com>
Signed-off-by: Chen-Yu Tsai <w...@csie.org>
Reviewed-by: Hans de Goede <hdego...@redhat.com>
Signed-off-by: Kishon Vijay Abraham I <kis...@ti.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/phy/phy-sun4i-usb.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/drivers/phy/phy-sun4i-usb.c
+++ b/drivers/phy/phy-sun4i-usb.c
@@ -40,6 +40,7 @@
 #include <linux/power_supply.h>
 #include <linux/regulator/consumer.h>
 #include <linux/reset.h>
+#include <linux/spinlock.h>
 #include <linux/usb/of.h>
 #include <linux/workqueue.h>
 
@@ -112,7 +113,7 @@ struct sun4i_usb_phy_data {
        void __iomem *base;
        const struct sun4i_usb_phy_cfg *cfg;
        enum usb_dr_mode dr_mode;
-       struct mutex mutex;
+       spinlock_t reg_lock; /* guard access to phyctl reg */
        struct sun4i_usb_phy {
                struct phy *phy;
                void __iomem *pmu;
@@ -179,9 +180,10 @@ static void sun4i_usb_phy_write(struct s
        struct sun4i_usb_phy_data *phy_data = to_sun4i_usb_phy_data(phy);
        u32 temp, usbc_bit = BIT(phy->index * 2);
        void __iomem *phyctl = phy_data->base + phy_data->cfg->phyctl_offset;
+       unsigned long flags;
        int i;
 
-       mutex_lock(&phy_data->mutex);
+       spin_lock_irqsave(&phy_data->reg_lock, flags);
 
        if (phy_data->cfg->type == sun8i_a33_phy) {
                /* A33 needs us to set phyctl to 0 explicitly */
@@ -218,7 +220,8 @@ static void sun4i_usb_phy_write(struct s
 
                data >>= 1;
        }
-       mutex_unlock(&phy_data->mutex);
+
+       spin_unlock_irqrestore(&phy_data->reg_lock, flags);
 }
 
 static void sun4i_usb_phy_passby(struct sun4i_usb_phy *phy, int enable)
@@ -577,7 +580,7 @@ static int sun4i_usb_phy_probe(struct pl
        if (!data)
                return -ENOMEM;
 
-       mutex_init(&data->mutex);
+       spin_lock_init(&data->reg_lock);
        INIT_DELAYED_WORK(&data->detect, sun4i_usb_phy0_id_vbus_det_scan);
        dev_set_drvdata(dev, data);
        data->cfg = of_device_get_match_data(dev);


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