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

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Message-ID: <883333c3-5685-905f-3e96-2c2498a22b8a@redhat.com>
Date:   Thu, 8 Sep 2016 12:16:12 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Chen-Yu Tsai <wens@...e.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     linux-arm-kernel@...ts.infradead.org, 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 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 ?

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);
>