[PATCH v3 2/3] ARM: imx: Add imx5 cpuidle driver

Sascha,

On Wed, May 9, 2012 at 3:02 AM, Sascha Hauer [off-list ref] wrote:

On Mon, May 07, 2012 at 04:16:46PM -0500, Robert Lee wrote:

quoted

Add imx5 cpuidle driver.

Signed-off-by: Robert Lee <redacted>
---
?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

quoted

? ? ? ? ? ? ? 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.

quoted

+ ? ? .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

quoted

?}

?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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