linux-kernel - Re: [PATCH] phy: meson-g12a-usb3-pcie: disable locking for cr

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Date:   Fri, 31 May 2019 20:06:29 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Neil Armstrong <narmstrong@...libre.com>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>
Subject: Re: [PATCH] phy: meson-g12a-usb3-pcie: disable locking for cr_regmap



On 31/05/19 7:52 PM, Neil Armstrong wrote:
> On 31/05/2019 12:35, Kishon Vijay Abraham I wrote:
>> Hi,
>>
>> On 31/05/19 4:01 PM, Neil Armstrong wrote:
>>> Fix the following BUG by disabling locking for the cr_regmap config.
>>
>> What caused the BUG in the first place? The commit log needs more details or
>> else this looks like a workaround to mask a BUG.
> 
> I thought it was pretty explicit, phy_g12a_usb3_pcie_cr_bus_read() sleeps
> with regmap_read_poll_timeout() while ran in spinlock_irq, caused by regmap fast_io = true
> 
> Locking is not needed in our case, this regmap is only used by the PHY init() callback.
> 
> Should I send a v2 with such explanation ?

yes, should atleast mention locking is not needed here.

-Kishon

> 
> Neil
> 
>>
>> Thanks
>> Kishon
>>
>>>
>>> BUG: sleeping function called from invalid context at drivers/phy/amlogic/phy-meson-g12a-usb3-pcie.c:85
>>> in_atomic(): 1, irqs_disabled(): 128, pid: 60, name: kworker/3:1
>>> [snip]
>>> Workqueue: events deferred_probe_work_func
>>> Call trace:
>>>  dump_backtrace+0x0/0x190
>>>  show_stack+0x14/0x20
>>>  dump_stack+0x90/0xb4
>>>  ___might_sleep+0xec/0x110
>>>  __might_sleep+0x50/0x88
>>>  phy_g12a_usb3_pcie_cr_bus_addr.isra.0+0x80/0x1a8
>>>  phy_g12a_usb3_pcie_cr_bus_read+0x34/0x1d8
>>>  _regmap_read+0x60/0xe0
>>>  _regmap_update_bits+0xc4/0x110
>>>  regmap_update_bits_base+0x60/0x90
>>>  phy_g12a_usb3_pcie_init+0xdc/0x210
>>>  phy_init+0x74/0xd0
>>>  dwc3_meson_g12a_probe+0x2cc/0x4d0
>>>  platform_drv_probe+0x50/0xa0
>>>  really_probe+0x20c/0x3b8
>>>  driver_probe_device+0x68/0x150
>>>  __device_attach_driver+0xa8/0x170
>>>  bus_for_each_drv+0x64/0xc8
>>>  __device_attach+0xd8/0x158
>>>  device_initial_probe+0x10/0x18
>>>  bus_probe_device+0x90/0x98
>>>  deferred_probe_work_func+0x94/0xe8
>>>  process_one_work+0x1e0/0x338
>>>  worker_thread+0x230/0x458
>>>  kthread+0x134/0x138
>>>  ret_from_fork+0x10/0x1c
>>>
>>> Fixes: 36077e16c050 ("phy: amlogic: Add Amlogic G12A USB3 + PCIE Combo PHY Driver")
>>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>>> ---
>>>  drivers/phy/amlogic/phy-meson-g12a-usb3-pcie.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/phy/amlogic/phy-meson-g12a-usb3-pcie.c b/drivers/phy/amlogic/phy-meson-g12a-usb3-pcie.c
>>> index 6233a7979a93..ac322d643c7a 100644
>>> --- a/drivers/phy/amlogic/phy-meson-g12a-usb3-pcie.c
>>> +++ b/drivers/phy/amlogic/phy-meson-g12a-usb3-pcie.c
>>> @@ -188,7 +188,7 @@ static const struct regmap_config phy_g12a_usb3_pcie_cr_regmap_conf = {
>>>  	.reg_read = phy_g12a_usb3_pcie_cr_bus_read,
>>>  	.reg_write = phy_g12a_usb3_pcie_cr_bus_write,
>>>  	.max_register = 0xffff,
>>> -	.fast_io = true,
>>> +	.disable_locking = true,
>>>  };
>>>  
>>>  static int phy_g12a_usb3_init(struct phy *phy)
>>>
>