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Date: Wed, 9 May 2012 09:27:02 -0500
From: Rob Lee <rob.lee@...aro.org>
To: Sascha Hauer <s.hauer@...gutronix.de>
Cc: kernel@...gutronix.de, shawn.guo@...aro.org,
amit.kucheria@...aro.org, daniel.lezcano@...aro.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linaro-dev@...ts.linaro.org, patches@...aro.org, jj@...osbits.net
Subject: Re: [PATCH v3 2/3] ARM: imx: Add imx5 cpuidle driver
Sascha,
On Wed, May 9, 2012 at 3:02 AM, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> On Mon, May 07, 2012 at 04:16:46PM -0500, Robert Lee wrote:
>> Add imx5 cpuidle driver.
>>
>> Signed-off-by: Robert Lee <rob.lee@...aro.org>
>> ---
>> arch/arm/mach-imx/mm-imx5.c | 42 +++++++++++++++++++++++++++++++++++++++---
>> 1 file changed, 39 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/mach-imx/mm-imx5.c b/arch/arm/mach-imx/mm-imx5.c
>> index d6b7e9f..0b3a4cc 100644
>> --- a/arch/arm/mach-imx/mm-imx5.c
>> +++ b/arch/arm/mach-imx/mm-imx5.c
>> @@ -20,26 +20,61 @@
>>
>> #include <mach/hardware.h>
>> #include <mach/common.h>
>> +#include <mach/cpuidle.h>
>> #include <mach/devices-common.h>
>> #include <mach/iomux-v3.h>
>>
>> static struct clk *gpc_dvfs_clk;
>>
>> -static void imx5_idle(void)
>> +static int imx5_idle(void)
>> {
>> + int ret = 0;
>> +
>> /* gpc clock is needed for SRPG */
>> if (gpc_dvfs_clk == NULL) {
>> gpc_dvfs_clk = clk_get(NULL, "gpc_dvfs");
>
> This clk_get should go away here and be moved somewhere to
> initialization. Also, if getting this clock fails we can still
> do regular cpu_do_idle. Additionally, if clk_get fails, we'll
> have a ERR_PTR value in gpc_dvfs_clk in which case the
> gpc_dvfs_clk == NULL won't trigger next time you are here and
> then you'll enable a nonexisting clock below.
>
Agree. I'd prefer to enable this clock during intialization and just
leave it running. It is supposed to be a very low power clock and I
couldn't measuring any power difference with and without it being
enabled
>> if (IS_ERR(gpc_dvfs_clk))
>> - return;
>> + return -ENODEV;
>> }
>> clk_enable(gpc_dvfs_clk);
>> mx5_cpu_lp_set(WAIT_UNCLOCKED_POWER_OFF);
>> if (!tzic_enable_wake())
>> cpu_do_idle();
>> + else
>> + ret = -EBUSY;
>> clk_disable(gpc_dvfs_clk);
>> +
>> + return ret;
>> +}
>> +
>> +static int imx5_cpuidle_enter(struct cpuidle_device *dev,
>> + struct cpuidle_driver *drv, int idx)
>> +{
>> + int ret;
>> +
>> + ret = imx5_idle();
>> +
>> + if (ret < 0)
>> + return ret;
>> +
>> + return idx;
>> }
>>
>> +static struct cpuidle_driver imx5_cpuidle_driver = {
>> + .name = "imx5_cpuidle",
>> + .owner = THIS_MODULE,
>> + .en_core_tk_irqen = 1,
>> + .states[0] = {
>> + .enter = imx5_cpuidle_enter,
>> + .exit_latency = 20, /* max latency at 160MHz */
>> + .target_residency = 1,
>> + .flags = CPUIDLE_FLAG_TIME_VALID,
>> + .name = "IMX5 SRPG",
>> + .desc = "CPU state retained,powered off",
>> + },
>
> I wonder why you don't add the default ARM_CPUIDLE_WFI_STATE_PWR state.
> The above is something different, right? It has a greater exit latency
> than ARM_CPUIDLE_WFI_STATE_PWR, so why don't we add it here aswell?
Yes and no. Yes this is a different state but no, it doesn't have a
significantly greater exit latency, or at least a large enough exit
latency to warrant an extra state in my opinion. According to the
i.MX5 documentation, the extra exit time beyond basic WFI required for
the "WAIT_UNCLOCKED_POWER_OFF" state is 500ns (this is due to a
difference in i.MX5 hardware implementation compared to all other ARM
platforms). In reality, it did require a few more microseconds to
perform in my testing just based on the extra register writes in
mx5_cpu_lp_set(). I'd like to clean up mx5_cpu_lp_set() and add a
global variable to track the previous state and to just exit out if
the new state is the same as the old. I could do this cleanup as part
of this patchset if you prefer that.
>
>> + .state_count = 1,
>> +};
>> +
>> /*
>> * Define the MX50 memory map.
>> */
>> @@ -103,7 +138,7 @@ void __init imx51_init_early(void)
>> mxc_set_cpu_type(MXC_CPU_MX51);
>> mxc_iomux_v3_init(MX51_IO_ADDRESS(MX51_IOMUXC_BASE_ADDR));
>> mxc_arch_reset_init(MX51_IO_ADDRESS(MX51_WDOG1_BASE_ADDR));
>> - arm_pm_idle = imx5_idle;
>> + arm_pm_idle = (void (*)(void))imx5_idle;
>
> Still this looks suspicious. Reading this will lead to the question why
> this prototype is casted. Please just add a imx5_pm_idle with the
> correct prototype.
Ok.
Thanks,
Rob
>
>> }
>>
>> void __init imx53_init_early(void)
>> @@ -238,4 +273,5 @@ void __init imx53_soc_init(void)
>> void __init imx51_init_late(void)
>> {
>> mx51_neon_fixup();
>> + imx_cpuidle_init(&imx5_cpuidle_driver);
>> }
>> --
>> 1.7.10
>>
>>
>
> --
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