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Subject: Re: [PATCH v1 1/2] soc/tegra: pmc: Turn powergates_lock into spinlock
To:     Dmitry Osipenko <digetx@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>
CC:     <linux-tegra@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20180830183635.4474-1-digetx@gmail.com>
 <7369869e-e58f-3760-d428-b00fb9cd28d9@nvidia.com>
 <57c3b1a6-0a60-613e-a4e7-5d66c199b860@gmail.com>
From:   Jon Hunter <jonathanh@nvidia.com>
Message-ID: <cf5b7db9-5109-a9c6-3352-068d205c1b98@nvidia.com>
Date:   Fri, 19 Oct 2018 13:17:39 +0100
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On 15/10/2018 14:52, Dmitry Osipenko wrote:
> On 10/15/18 3:52 PM, Jon Hunter wrote:
>>
>> On 30/08/18 19:36, Dmitry Osipenko wrote:
>>> This fixes splats like the one below if CONFIG_DEBUG_ATOMIC_SLEEP=y
>>> and machine (Tegra30) booted with SMP=n or all secondary CPU's are put
>>> offline.
>>>
>>>  BUG: sleeping function called from invalid context at kernel/locking/mutex.c:254
>>>  in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/0
>>>  CPU: 0 PID: 0 Comm: swapper/0 Tainted: G         C        4.18.0-next-20180821-00180-gc3ebb6544e44-dirty #823
>>>  Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
>>>  [<c01134f4>] (unwind_backtrace) from [<c010db2c>] (show_stack+0x20/0x24)
>>>  [<c010db2c>] (show_stack) from [<c0bd0f3c>] (dump_stack+0x94/0xa8)
>>>  [<c0bd0f3c>] (dump_stack) from [<c0151df8>] (___might_sleep+0x13c/0x174)
>>>  [<c0151df8>] (___might_sleep) from [<c0151ea0>] (__might_sleep+0x70/0xa8)
>>>  [<c0151ea0>] (__might_sleep) from [<c0bec2b8>] (mutex_lock+0x2c/0x70)
>>>  [<c0bec2b8>] (mutex_lock) from [<c0589844>] (tegra_powergate_is_powered+0x44/0xa8)
>>>  [<c0589844>] (tegra_powergate_is_powered) from [<c0581a60>] (tegra30_cpu_rail_off_ready+0x30/0x74)
>>>  [<c0581a60>] (tegra30_cpu_rail_off_ready) from [<c0122244>] (tegra30_idle_lp2+0xa0/0x108)
>>>  [<c0122244>] (tegra30_idle_lp2) from [<c0853438>] (cpuidle_enter_state+0x140/0x540)
>>>  [<c0853438>] (cpuidle_enter_state) from [<c08538a4>] (cpuidle_enter+0x40/0x4c)
>>>  [<c08538a4>] (cpuidle_enter) from [<c01595e0>] (call_cpuidle+0x30/0x48)
>>>  [<c01595e0>] (call_cpuidle) from [<c01599f8>] (do_idle+0x238/0x28c)
>>>  [<c01599f8>] (do_idle) from [<c0159d28>] (cpu_startup_entry+0x28/0x2c)
>>>  [<c0159d28>] (cpu_startup_entry) from [<c0be76c8>] (rest_init+0xd8/0xdc)
>>>  [<c0be76c8>] (rest_init) from [<c1200f50>] (start_kernel+0x41c/0x430)
>>
>> Given the above, rather than converting to a spinlock I wonder if we are
>> just better off dropping the mutex completely from
>> tegra_powergate_is_powered()? Otherwise ...
>>
>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>>> ---
>>>  drivers/soc/tegra/pmc.c | 36 ++++++++++++++++++------------------
>>>  1 file changed, 18 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
>>> index 2d6f3fcf3211..d6bc9f66f1cd 100644
>>> --- a/drivers/soc/tegra/pmc.c
>>> +++ b/drivers/soc/tegra/pmc.c
>>> @@ -186,7 +186,7 @@ struct tegra_pmc_soc {
>>>   * @lp0_vec_phys: physical base address of the LP0 warm boot code
>>>   * @lp0_vec_size: size of the LP0 warm boot code
>>>   * @powergates_available: Bitmap of available power gates
>>> - * @powergates_lock: mutex for power gate register access
>>> + * @powergates_lock: lock for power gate register access
>>>   */
>>>  struct tegra_pmc {
>>>  	struct device *dev;
>>> @@ -215,7 +215,7 @@ struct tegra_pmc {
>>>  	u32 lp0_vec_size;
>>>  	DECLARE_BITMAP(powergates_available, TEGRA_POWERGATE_MAX);
>>>  
>>> -	struct mutex powergates_lock;
>>> +	spinlock_t powergates_lock;
>>>  };
>>>  
>>>  static struct tegra_pmc *pmc = &(struct tegra_pmc) {
>>> @@ -288,10 +288,10 @@ static int tegra_powergate_set(unsigned int id, bool new_state)
>>>  	if (id == TEGRA_POWERGATE_3D && pmc->soc->has_gpu_clamps)
>>>  		return -EINVAL;
>>>  
>>> -	mutex_lock(&pmc->powergates_lock);
>>> +	spin_lock(&pmc->powergates_lock);
>>>  
>>>  	if (tegra_powergate_state(id) == new_state) {
>>> -		mutex_unlock(&pmc->powergates_lock);
>>> +		spin_unlock(&pmc->powergates_lock);
>>>  		return 0;
>>>  	}
>>>  
>>> @@ -300,7 +300,7 @@ static int tegra_powergate_set(unsigned int id, bool new_state)
>>>  	err = readx_poll_timeout(tegra_powergate_state, id, status,
>>>  				 status == new_state, 10, 100000);
>>>  
>>> -	mutex_unlock(&pmc->powergates_lock);
>>> +	spin_unlock(&pmc->powergates_lock);
>>
>> ... the above readx_poll_timeout needs to be converted to the atomic
>> version. Furthermore, the above 100ms timeout is probably not suited to
>> spinlock.
> 
> It's converted in the second patch. Seems mutex indeed could be dropped from tegra_powergate_is_powered, at least for now I can't recall why decided to keep the locking. Thank you for the review, I'll try to drop the mutex and come back with v2 if it will be fine.

Sorry if you were waiting for my response, but yes sounds good to me.

Cheers
Jon

-- 
nvpublic