Re: [PATCH] phy: meson-g12a-usb3-pcie: disable locking for cr_regmap

From: Neil Armstrong <narmstrong@baylibre.com>
To: Kishon Vijay Abraham I <kishon@ti.com>
Cc: linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] phy: meson-g12a-usb3-pcie: disable locking for cr_regmap
Date: Fri, 31 May 2019 16:22:07 +0200	[thread overview]
Message-ID: <2a354f12-61a8-6b4e-8006-e442245a92ec@baylibre.com> (raw)
In-Reply-To: <4dc22a2e-66ca-0556-3aa3-4ed8887c2b1b@ti.com>

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 ?

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@baylibre.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)
>>

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