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Date:	Tue, 06 Oct 2015 10:55:59 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Felipe Balbi <balbi@...com>, John Youn <John.Youn@...opsys.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>
Cc:	Robert Baldyga <r.baldyga@...sung.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v4 4/4] usb: dwc2: refactor common low-level hw code to
 platform.c

Hello,

On 2015-10-06 01:27, Felipe Balbi wrote:
> John Youn <John.Youn@...opsys.com> writes:
>
> Hi,
>
>> On 10/2/2015 12:45 AM, Marek Szyprowski wrote:
>>> DWC2 module on some platforms needs three additional hardware
>>> resources: phy controller, clock and power supply. All of them must be
>>> enabled/activated to properly initialize and operate. This was initially
>>> handled in s3c-hsotg driver, which has been converted to 'gadget' part
>>> of dwc2 driver. Unfortunately, not all of this code got moved to common
>>> platform code, what resulted in accessing DWC2 registers without
>>> enabling low-level hardware resources. This fails for example on Exynos
>>> SoCs. This patch moves all the code for managing those resources to
>>> common platform.c file and provides convenient wrappers for controlling
>>> them.
>>>
>>> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>>> ---
>>> Changelog:
>>> v4:
>>> - fixed broken conditional compilation and adjusted comments in dwc2_hsotg
>>>    structure documentation
>>>
>>> v3:
>>> - rebased onto latest 'testing/next' from Felipe Balbi (includes
>>>    s3c_hsotg -> dwc2 rename)
>>>
>>> v2:
>>> - moved setting of ll_hw_enabled flag to enable/disable functions,
>>>    as suggested by John Youn
>>> - moved setting of phy width to dwc2_lowlevel_init function
>>> ---
>>>   drivers/usb/dwc2/core.h     |  24 +++--
>>>   drivers/usb/dwc2/gadget.c   | 193 ++++--------------------------------
>>>   drivers/usb/dwc2/platform.c | 234 +++++++++++++++++++++++++++++++++++++-------
>>>   3 files changed, 228 insertions(+), 223 deletions(-)
>>>
>> Hi Marek,
>>
>> I still see lockdep warnings.
>>
>> Any ideas about these?
>>
>>
>> [ 1618.179611] ======================================================
>> [ 1618.179612] [ INFO: possible circular locking dependency detected ]
>> [ 1618.179613] 4.3.0-rc3-snps-00125-g744fd93 #28 Not tainted
>> [ 1618.179614] -------------------------------------------------------
>> [ 1618.179615] modprobe/2658 is trying to acquire lock:
>> [ 1618.179616]  (&hsotg->init_mutex){+.+.+.}, at: [<ffffffffc043aa3c>] dwc2_hsotg_udc_start+0x5c/0x200 [dwc2]
>> [ 1618.179622]
>> [ 1618.179622] but task is already holding lock:
>> [ 1618.179623]  (udc_lock){+.+.+.}, at: [<ffffffffc0374b8a>] usb_gadget_probe_driver+0x3a/0xd0 [udc_core]
>> [ 1618.179627]
>> [ 1618.179627] which lock already depends on the new lock.
>> [ 1618.179627]
>> [ 1618.179628]
>> [ 1618.179628] the existing dependency chain (in reverse order) is:
>> [ 1618.179629]
>> [ 1618.179629] -> #1 (udc_lock){+.+.+.}:
>> [ 1618.179631]        [<ffffffff810da56d>] lock_acquire+0xdd/0x1f0
>> [ 1618.179635]        [<ffffffff818658a6>] mutex_lock_nested+0x76/0x3e0
>> [ 1618.179638]        [<ffffffffc0374da7>] usb_add_gadget_udc_release+0x187/0x240 [udc_core]
>> [ 1618.179640]        [<ffffffffc0374e70>] usb_add_gadget_udc+0x10/0x20 [udc_core]
>> [ 1618.179642]        [<ffffffffc043b30c>] dwc2_gadget_init+0x47c/0x580 [dwc2]
>> [ 1618.179645]        [<ffffffffc042d2f2>] dwc2_driver_probe+0x422/0x4b0 [dwc2]
>> [ 1618.179648]        [<ffffffff8153fe94>] platform_drv_probe+0x34/0x90
>> [ 1618.179650]        [<ffffffff8153db54>] driver_probe_device+0x224/0x480
>> [ 1618.179652]        [<ffffffff8153deb1>] __device_attach_driver+0x71/0xa0
>> [ 1618.179654]        [<ffffffff8153b78d>] bus_for_each_drv+0x5d/0x90
>> [ 1618.179655]        [<ffffffff8153d83f>] __device_attach+0xbf/0x140
>> [ 1618.179657]        [<ffffffff8153df23>] device_initial_probe+0x13/0x20
>> [ 1618.179658]        [<ffffffff8153cb03>] bus_probe_device+0xa3/0xb0
>> [ 1618.179660]        [<ffffffff8153a76d>] device_add+0x40d/0x690
>> [ 1618.179661]        [<ffffffff8153fb81>] platform_device_add+0x111/0x270
>> [ 1618.179663]        [<ffffffffc0394128>] dwc2_pci_probe+0xe8/0x1d2 [dwc2_pci]
>> [ 1618.179665]        [<ffffffff81446085>] local_pci_probe+0x45/0xa0
>> [ 1618.179668]        [<ffffffff81447451>] pci_device_probe+0xe1/0x130
>> [ 1618.179669]        [<ffffffff8153db54>] driver_probe_device+0x224/0x480
>> [ 1618.179671]        [<ffffffff8153de38>] __driver_attach+0x88/0x90
>> [ 1618.179672]        [<ffffffff8153b6d6>] bus_for_each_dev+0x66/0xa0
>> [ 1618.179674]        [<ffffffff8153d31e>] driver_attach+0x1e/0x20
>> [ 1618.179675]        [<ffffffff8153ce8e>] bus_add_driver+0x1ee/0x280
>> [ 1618.179677]        [<ffffffff8153e930>] driver_register+0x60/0xe0
>> [ 1618.179678]        [<ffffffff81445a60>] __pci_register_driver+0x60/0x70
>> [ 1618.179680]        [<ffffffffc000601e>] 0xffffffffc000601e
>> [ 1618.179681]        [<ffffffff81002123>] do_one_initcall+0xb3/0x200
>> [ 1618.179684]        [<ffffffff811a8a41>] do_init_module+0x5f/0x1e7
>> [ 1618.179687]        [<ffffffff81120e48>] load_module+0x21a8/0x2840
>> [ 1618.179689]        [<ffffffff8112170a>] SyS_finit_module+0x9a/0xc0
>> [ 1618.179691]        [<ffffffff81869c36>] entry_SYSCALL_64_fastpath+0x16/0x7a
>> [ 1618.179693]
>> [ 1618.179693] -> #0 (&hsotg->init_mutex){+.+.+.}:
>> [ 1618.179695]        [<ffffffff810d97f5>] __lock_acquire+0x1d35/0x1db0
>> [ 1618.179697]        [<ffffffff810da56d>] lock_acquire+0xdd/0x1f0
>> [ 1618.179698]        [<ffffffff818658a6>] mutex_lock_nested+0x76/0x3e0
>> [ 1618.179700]        [<ffffffffc043aa3c>] dwc2_hsotg_udc_start+0x5c/0x200 [dwc2]
>> [ 1618.179703]        [<ffffffffc0374a34>] udc_bind_to_driver+0xa4/0x100 [udc_core]
>> [ 1618.179705]        [<ffffffffc0374bca>] usb_gadget_probe_driver+0x7a/0xd0 [udc_core]
>> [ 1618.179707]        [<ffffffffc059a674>] usb_composite_probe+0xa4/0xc0 [libcomposite]
>> [ 1618.179709]        [<ffffffffc0474010>] msg_init+0x10/0x1000 [g_mass_storage]
>> [ 1618.179711]        [<ffffffff81002123>] do_one_initcall+0xb3/0x200
>> [ 1618.179713]        [<ffffffff811a8a41>] do_init_module+0x5f/0x1e7
>> [ 1618.179714]        [<ffffffff81120e48>] load_module+0x21a8/0x2840
>> [ 1618.179716]        [<ffffffff8112170a>] SyS_finit_module+0x9a/0xc0
>> [ 1618.179717]        [<ffffffff81869c36>] entry_SYSCALL_64_fastpath+0x16/0x7a
>> [ 1618.179719]
>> [ 1618.179719] other info that might help us debug this:
>> [ 1618.179719]
>> [ 1618.179720]  Possible unsafe locking scenario:
>> [ 1618.179720]
>> [ 1618.179721]        CPU0                    CPU1
>> [ 1618.179722]        ----                    ----
>> [ 1618.179722]   lock(udc_lock);
>> [ 1618.179723]                                lock(&hsotg->init_mutex);
> It seems like init_mutex is completely unnecessary in this driver. In
> fact, why are you trying to hold a mutex while inside a spinlock ?

init_mutex is a leftover from the time, when s3c-hsotg driver didn't 
implement
proper pull up/down control and emulated it by enabling disabling phy. 
It can
be removed now. btw, the possible lockup pointed by John is an 
interaction of
two mutexes, not a case of taking mutex under a spinlock.

I will send an updated patch in a few minutes.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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