linux-kernel - Re: [PATCH 2/2] ARM: imx: cpuidle-imx6q: configure CCM to RUN mode when CPU is active

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Message-ID: <20180125021957.GA19344@shlinux2>
Date:   Thu, 25 Jan 2018 10:19:57 +0800
From:   Peng Fan <van.freenix@...il.com>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Peng Fan <peng.fan@....com>, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com, aisheng.dong@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] ARM: imx: cpuidle-imx6q: configure CCM to RUN mode
 when CPU is active

Hi Lucas,
On Wed, Jan 24, 2018 at 12:16:25PM +0100, Lucas Stach wrote:
>Hi Peng,
>
>Am Samstag, den 30.12.2017, 21:53 +0800 schrieb Peng Fan:
>> There are two states in i.MX6Q cpuidle driver.
>> state[1]: ARM WFI mode
>> state[2]: i.MX6Q WAIT mode
>> 
>> Take i.MX6DL as example, think out such a case:
>> 1. CPU0/1 both run at normal mode
>> 2. On CPU0, `sleep 1` is executed. And there are no workload on CPU1.
>> 3. CPU0 first runs into state[2] and 'wfi' instruction. Switched to
>> use
>> ??????GPT broadcast.
>> 4. CPU1 runs into state[2] and configure CCM to WAIT MODE,
>> ??????then 'wfi' instruction. Now arm_clk and local timer clock are
>> ??????shutdown. Switched to use GPT broadcast
>> 5. GPT broadcast timer interrupt comes to GPC/GIC, then CPU0 wakes
>> up.
>> ??????CPU0 switched to use arm local timer. CPU1 is still sleeping.
>> 6. No workload on CPU0, CPU0 runs into state[1]. But CCM register
>> ??????is still not restored to Normal RUN mode. 'wfi' + CCM WAIT will
>> ??????cause arm_clk and arm core clk.
>> ??????Now CPU0 stops, which is not correct.
>> 
>> So, need to make sure CCM configured to RUN mode when any cpu exit
>> state[2].
>> 
>> In this patch,
>> When CPU exits state[2], it configures CCM to RUN mode.
>> When all CPUs enters state[2], the last CPU needs to check
>> whether it's ok to configure CCM to WAIT mode or not.
>
>To me this patch seems like we are adding duct tape to fix the issue.??
>
>It seems the whole master_lock thing doesn't properly work when the CPU
>that is woken up by the timer broadcast isn't the last CPU going to
>sleep. We should probably try to come up with a way to simplify this
>whole master dance, instead of adding yet more complexity.

The master_lock is used to protect multiple CPUS runs into State[1].
It could not be used to protect the CPU runs into State[0].

The patch is to make sure that before arm clk turned off, need to check
whether all the cpus are in State[1]. And the cpu who first wake up from
State[1], need to configure CCM to RUN mode.

This patch has been integrated into vendor kernel and fixed customer's issue.
I could not think out of a better solution to restructure the master lock,
and this may introduce new issues.

Thanks,
Peng.

>
>Regards,
>Lucas
>
>> Signed-off-by: Peng Fan <peng.fan@....com>
>> ---
>> 
>> V1:
>> ??This is to upstream patch:
>> ??http://git.freescale.com/git/cgit.cgi/imx/linux-imx.git/commit/?h=im
>> x_4.9.11_1.0.0_ga&id=0d980646ee068b92db71fd5e4e4efcbc33749cbd
>> 
>> ??arch/arm/mach-imx/cpuidle-imx6q.c | 3 +++
>> ??1 file changed, 3 insertions(+)
>> 
>> diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-
>> imx/cpuidle-imx6q.c
>> index bfeb25aaf9a2..4d342e2fdfe6 100644
>> --- a/arch/arm/mach-imx/cpuidle-imx6q.c
>> +++ b/arch/arm/mach-imx/cpuidle-imx6q.c
>> @@ -30,6 +30,8 @@ static int imx6q_enter_wait(struct cpuidle_device
>> *dev,
>> ??		if (!spin_trylock(&master_lock))
>> ??			goto idle;
>> ??		imx6_set_lpm(WAIT_UNCLOCKED);
>> +		if (atomic_read(&master) != num_online_cpus())
>> +			imx6_set_lpm(WAIT_CLOCKED);
>> ??		cpu_do_idle();
>> ??		imx6_set_lpm(WAIT_CLOCKED);
>> ??		spin_unlock(&master_lock);
>> @@ -41,6 +43,7 @@ static int imx6q_enter_wait(struct cpuidle_device
>> *dev,
>> ??done:
>> ??	atomic_dec(&master);
>> ??
>> +	imx6_set_lpm(WAIT_CLOCKED);
>> ??	return index;
>> ??}
>> ??

--