linux-kernel - Re: [PATCH] phy: sun4i-usb: Use spinlock to guard phyctl register access

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Message-ID: <a7465592-39f8-beef-d478-47ece3fdd1f2@redhat.com>
Date:   Thu, 8 Sep 2016 13:57:56 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] phy: sun4i-usb: Use spinlock to guard phyctl register
 access

Hi,

On 08-09-16 12:24, Chen-Yu Tsai wrote:
> On Thu, Sep 8, 2016 at 6:16 PM, Hans de Goede <hdegoede@...hat.com> wrote:
>> Hi,
>>
>>
>> On 08-09-16 05:14, Chen-Yu Tsai wrote:
>>>
>>> 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 <hdegoede@...hat.com>
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>>
>>
>> Good catch, but you're actually replacing the locking calls in the only
>> user of sun4i_usb_phy_data.mutex, so after your patch it is no longer
>> used anywhere. Can you do a v2 just outright replacing it with a
>> spinlock please ?
>
> Ah. I misread the other use of mutex_lock, which is actually using
> the mutex in struct phy. Sure I'll just replace it.
>
> After sending this patch I wondered if I should have used
> spin_lock_irqsave though.

Good point, yes please use spin_lock_irqsave, I believe this
code path may get called outside of irq handling so using
spin_lock_irqsave is the right thing todo.

Regards,

Hans


>
> ChenYu
>
>>
>> Thanks,
>>
>> Hans
>>
>>
>>
>>
>>> ---
>>>  drivers/phy/phy-sun4i-usb.c | 8 ++++++--
>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/phy/phy-sun4i-usb.c b/drivers/phy/phy-sun4i-usb.c
>>> index fcf4d95ecc6d..ae4ac5457c64 100644
>>> --- 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>
>>>
>>> @@ -115,6 +116,7 @@ struct sun4i_usb_phy_data {
>>>         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;
>>> @@ -183,7 +185,7 @@ static void sun4i_usb_phy_write(struct sun4i_usb_phy
>>> *phy, u32 addr, u32 data,
>>>         void __iomem *phyctl = phy_data->base +
>>> phy_data->cfg->phyctl_offset;
>>>         int i;
>>>
>>> -       mutex_lock(&phy_data->mutex);
>>> +       spin_lock(&phy_data->reg_lock);
>>>
>>>         if (phy_data->cfg->type == sun8i_a33_phy ||
>>>             phy_data->cfg->type == sun50i_a64_phy) {
>>> @@ -221,7 +223,8 @@ static void sun4i_usb_phy_write(struct sun4i_usb_phy
>>> *phy, u32 addr, u32 data,
>>>
>>>                 data >>= 1;
>>>         }
>>> -       mutex_unlock(&phy_data->mutex);
>>> +
>>> +       spin_unlock(&phy_data->reg_lock);
>>>  }
>>>
>>>  static void sun4i_usb_phy_passby(struct sun4i_usb_phy *phy, int enable)
>>> @@ -583,6 +586,7 @@ static int sun4i_usb_phy_probe(struct platform_device
>>> *pdev)
>>>                 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);
>>>
>>