RE: [PATCH 1/1] OMAP: I2C: Add mpu wake up latency constraint in i2c

[Kalle Jokiniemi <kalle.jokiniemi@digia.com>]

Hi,

On Mon, 2009-10-05 at 20:08 +0300, Pandita, Vikram wrote:
> Jokiniemi
> 
> >-----Original Message-----
> >From: linux-omap-owner@vger.kernel.org [mailto:linux-omap-owner@vger.kernel.org] On Behalf Of Kalle
> >Jokiniemi
> >Sent: Thursday, September 17, 2009 11:29 AM
> >To: khilman@deeprootsystems.com
> >Cc: jhnikula@gmail.com; linux-omap@vger.kernel.org; Kalle Jokiniemi
> >Subject: [PATCH 1/1] OMAP: I2C: Add mpu wake up latency constraint in i2c
> >
> >While waiting for completion of the i2c transfer, the
> >MPU could hit OFF mode and cause several msecs of
> >delay that made i2c transfers fail more often. The
> 
> How many bytes i2c read were you doing, that failed?

This I don't know. I was monitoring average transfer times from
clk_enable to clk_disable in i2c-omap.c and I noticed the transfers
timed out to 1000ms several times. Hence the conclusion that something
went wrong (this is what I was referring to with "fail more often").


> 
> What OPP are you in when you observe these failures? 
> VDD1:OPP?

I had on-demand governor in use, but device was mostly idling, so OPP2
probably.


> 
> >extra delays and subsequent re-trys cause i2c clocks
> >to be active more often. This has also an negative
> >effect on power consumption.
> >
> >Added a constraint that allows MPU to wake up in few
> >hundred usecs, which is roughly the average i2c wait
> >period.
> 
> How did you arrive at the number 500us for the wakeup latency?

This was about the average time that I observed i2c-transfers to be
(from clk_enable to clk_disable), when off mode was not enabled.

> 
> On Zoom2 with Synaptic touch screen controller on I2C-2,
> at vdd1:opp1 we need to put a wakeup latency of 400us else we see data corruption.

Hmm, I guess you are using new cpu idle latency numbers on zoom2, since
on current pm-branch code 500us==400us==C3 C-state. But I'll repost with
400us, it might make a difference once those C-state latency numbers are
updated in pm-branch.

- Kalle

> 
> Our case is doing a write of 1 byte followed by read of 16 bytes.
> 
> >
> >The constraint function is passed as platform data from
> >plat-omap/i2c.c and applied only on OMAP34XX devices.
> >
> >Signed-off-by: Kalle Jokiniemi <kalle.jokiniemi@digia.com>
> >---
> > arch/arm/plat-omap/i2c.c      |   49 +++++++++++++++++++++++++++++++----------
> > drivers/i2c/busses/i2c-omap.c |   17 +++++++++++---
> > include/linux/i2c-omap.h      |    9 +++++++
> > 3 files changed, 59 insertions(+), 16 deletions(-)
> > create mode 100644 include/linux/i2c-omap.h
> >
> >diff --git a/arch/arm/plat-omap/i2c.c b/arch/arm/plat-omap/i2c.c
> >index 8b84839..d43d0ad 100644
> >--- a/arch/arm/plat-omap/i2c.c
> >+++ b/arch/arm/plat-omap/i2c.c
> >@@ -26,8 +26,10 @@
> > #include <linux/kernel.h>
> > #include <linux/platform_device.h>
> > #include <linux/i2c.h>
> >+#include <linux/i2c-omap.h>
> > #include <mach/irqs.h>
> > #include <mach/mux.h>
> >+#include <mach/omap-pm.h>
> >
> > #define OMAP_I2C_SIZE		0x3f
> > #define OMAP1_I2C_BASE		0xfffb3800
> >@@ -69,14 +71,14 @@ static struct resource i2c_resources[][2] = {
> > 		},					\
> > 	}
> >
> >-static u32 i2c_rate[ARRAY_SIZE(i2c_resources)];
> >+static struct omap_i2c_bus_platform_data i2c_pdata[ARRAY_SIZE(i2c_resources)];
> > static struct platform_device omap_i2c_devices[] = {
> >-	I2C_DEV_BUILDER(1, i2c_resources[0], &i2c_rate[0]),
> >+	I2C_DEV_BUILDER(1, i2c_resources[0], &i2c_pdata[0]),
> > #if	defined(CONFIG_ARCH_OMAP24XX) || defined(CONFIG_ARCH_OMAP34XX)
> >-	I2C_DEV_BUILDER(2, i2c_resources[1], &i2c_rate[1]),
> >+	I2C_DEV_BUILDER(2, i2c_resources[1], &i2c_pdata[1]),
> > #endif
> > #if	defined(CONFIG_ARCH_OMAP34XX)
> >-	I2C_DEV_BUILDER(3, i2c_resources[2], &i2c_rate[2]),
> >+	I2C_DEV_BUILDER(3, i2c_resources[2], &i2c_pdata[2]),
> > #endif
> > };
> >
> >@@ -100,6 +102,25 @@ static const int omap34xx_pins[][2] = {};
> >
> > #define OMAP_I2C_CMDLINE_SETUP	(BIT(31))
> >
> >+/**
> >+ * omap_i2c_set_wfc_mpu_wkup_lat - sets mpu wake up constraint
> >+ * @dev:	i2c bus device pointer
> >+ * @set:	set or clear constraints
> >+ *
> >+ * When waiting for completion of a i2c transfer, we need to set a wake up
> >+ * latency constraint for the MPU. This is to ensure quick enough wakeup
> >+ * from idle, when transfer completes.
> >+ */
> >+#ifdef CONFIG_ARCH_OMAP34XX
> >+static void omap_i2c_set_wfc_mpu_wkup_lat(struct device *dev, int set)
> >+{
> >+	omap_pm_set_max_mpu_wakeup_lat(dev, set ? 500 : -1);
> >+}
> >+#else
> >+static inline void omap_i2c_set_wfc_mpu_wkup_lat(struct device *dev, int set)
> >+{; }
> >+#endif
> >+
> > static void __init omap_i2c_mux_pins(int bus)
> > {
> > 	int scl, sda;
> >@@ -180,8 +201,8 @@ static int __init omap_i2c_bus_setup(char *str)
> > 	get_options(str, 3, ints);
> > 	if (ints[0] < 2 || ints[1] < 1 || ints[1] > ports)
> > 		return 0;
> >-	i2c_rate[ints[1] - 1] = ints[2];
> >-	i2c_rate[ints[1] - 1] |= OMAP_I2C_CMDLINE_SETUP;
> >+	i2c_pdata[ints[1] - 1].clkrate = ints[2];
> >+	i2c_pdata[ints[1] - 1].clkrate |= OMAP_I2C_CMDLINE_SETUP;
> >
> > 	return 1;
> > }
> >@@ -195,9 +216,11 @@ static int __init omap_register_i2c_bus_cmdline(void)
> > {
> > 	int i, err = 0;
> >
> >-	for (i = 0; i < ARRAY_SIZE(i2c_rate); i++)
> >-		if (i2c_rate[i] & OMAP_I2C_CMDLINE_SETUP) {
> >-			i2c_rate[i] &= ~OMAP_I2C_CMDLINE_SETUP;
> >+	for (i = 0; i < ARRAY_SIZE(i2c_pdata); i++)
> >+		if (i2c_pdata[i].clkrate & OMAP_I2C_CMDLINE_SETUP) {
> >+			i2c_pdata[i].clkrate &= ~OMAP_I2C_CMDLINE_SETUP;
> >+			i2c_pdata[i].set_mpu_wkup_lat =
> >+						omap_i2c_set_wfc_mpu_wkup_lat;
> > 			err = omap_i2c_add_bus(i + 1);
> > 			if (err)
> > 				goto out;
> >@@ -231,9 +254,11 @@ int __init omap_register_i2c_bus(int bus_id, u32 clkrate,
> > 			return err;
> > 	}
> >
> >-	if (!i2c_rate[bus_id - 1])
> >-		i2c_rate[bus_id - 1] = clkrate;
> >-	i2c_rate[bus_id - 1] &= ~OMAP_I2C_CMDLINE_SETUP;
> >+	if (!i2c_pdata[bus_id - 1].clkrate)
> >+		i2c_pdata[bus_id - 1].clkrate = clkrate;
> >+
> >+	i2c_pdata[bus_id - 1].set_mpu_wkup_lat = omap_i2c_set_wfc_mpu_wkup_lat;
> >+	i2c_pdata[bus_id - 1].clkrate &= ~OMAP_I2C_CMDLINE_SETUP;
> >
> > 	return omap_i2c_add_bus(bus_id);
> > }
> >diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> >index 75bf3ad..da6d276 100644
> >--- a/drivers/i2c/busses/i2c-omap.c
> >+++ b/drivers/i2c/busses/i2c-omap.c
> >@@ -37,6 +37,7 @@
> > #include <linux/platform_device.h>
> > #include <linux/clk.h>
> > #include <linux/io.h>
> >+#include <linux/i2c-omap.h>
> >
> > /* I2C controller revisions */
> > #define OMAP_I2C_REV_2			0x20
> >@@ -165,6 +166,8 @@ struct omap_i2c_dev {
> > 	struct clk		*fclk;		/* Functional clock */
> > 	struct completion	cmd_complete;
> > 	struct resource		*ioarea;
> >+	void			(*set_mpu_wkup_lat)(struct device *dev,
> >+						    int set);
> > 	u32			speed;		/* Speed of bus in Khz */
> > 	u16			cmd_err;
> > 	u8			*buf;
> >@@ -526,8 +529,10 @@ static int omap_i2c_xfer_msg(struct i2c_adapter *adap,
> > 	 * REVISIT: We should abort the transfer on signals, but the bus goes
> > 	 * into arbitration and we're currently unable to recover from it.
> > 	 */
> >+	dev->set_mpu_wkup_lat(dev->dev, 1);
> > 	r = wait_for_completion_timeout(&dev->cmd_complete,
> > 					OMAP_I2C_TIMEOUT);
> >+	dev->set_mpu_wkup_lat(dev->dev, 0);
> > 	dev->buf_len = 0;
> > 	if (r < 0)
> > 		return r;
> >@@ -844,6 +849,7 @@ omap_i2c_probe(struct platform_device *pdev)
> > 	struct omap_i2c_dev	*dev;
> > 	struct i2c_adapter	*adap;
> > 	struct resource		*mem, *irq, *ioarea;
> >+	struct omap_i2c_bus_platform_data *pdata = pdev->dev.platform_data;
> > 	irq_handler_t isr;
> > 	int r;
> > 	u32 speed = 0;
> >@@ -873,10 +879,13 @@ omap_i2c_probe(struct platform_device *pdev)
> > 		goto err_release_region;
> > 	}
> >
> >-	if (pdev->dev.platform_data != NULL)
> >-		speed = *(u32 *)pdev->dev.platform_data;
> >-	else
> >-		speed = 100;	/* Defualt speed */
> >+	if (pdata != NULL) {
> >+		speed = pdata->clkrate;
> >+		dev->set_mpu_wkup_lat = pdata->set_mpu_wkup_lat;
> >+	} else {
> >+		speed = 100;	/* Default speed */
> >+		dev->set_mpu_wkup_lat = NULL;
> >+	}
> >
> > 	dev->speed = speed;
> > 	dev->idle = 1;
> >diff --git a/include/linux/i2c-omap.h b/include/linux/i2c-omap.h
> >new file mode 100644
> >index 0000000..1362fba
> >--- /dev/null
> >+++ b/include/linux/i2c-omap.h
> >@@ -0,0 +1,9 @@
> >+#ifndef __I2C_OMAP_H__
> >+#define __I2C_OMAP_H__
> >+
> >+struct omap_i2c_bus_platform_data {
> >+	u32		clkrate;
> >+	void		(*set_mpu_wkup_lat)(struct device *dev, int set);
> >+};
> >+
> >+#endif
> >--
> >1.5.4.3
> >
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