i2c-omap: 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
extra delays and subsequent re-trys cause i2c clocks
to be active more often. This has also an negative
effect on power consumption.

Created a mechanism for passing and using the
constraint setting function in driver code. The used
mpu wake up latency constraints are now set individually
per bus, and they are calculated based on clock rate
and fifo size.

Thanks to Jarkko Nikula, Moiz Sonasath, Paul Walmsley,
and Nishanth Menon for tuning out the details of
this patch.

Updates by Kevin as requested by Tony:

- Remove omap_set_i2c_constraint_func() in favor of conditionally
  adding the flag in omap_i2c_add_bus() in order to keep all the OMAP
  conditional checking in a single location.
- Update set_mpu_wkup_lat prototypes to match OMAP PM layer so
  OMAP PM function can be used directly in pdata.

Cc: Moiz Sonasath <m-sonasath@ti.com>
Cc: Jarkko Nikula <jhnikula@gmail.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Nishanth Menon <nm@ti.com>
Signed-off-by: Kalle Jokiniemi <kalle.jokiniemi@digia.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

1 files changed, 20 insertions, 4 deletions

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index 46111ff18133..42c0b9108c7f 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -38,6 +38,7 @@
 #include <linux/clk.h>
 #include <linux/io.h>
 #include <linux/slab.h>
+#include <linux/i2c-omap.h>
 
 /* I2C controller revisions */
 #define OMAP_I2C_REV_2                  0x20
@@ -175,6 +176,9 @@ struct omap_i2c_dev {
         struct clk              *fclk;          /* Functional clock */
         struct completion       cmd_complete;
         struct resource         *ioarea;
+        u32                     latency;        /* maximum mpu wkup latency */
+        void                    (*set_mpu_wkup_lat)(struct device *dev,
+                                                    long latency);
         u32                     speed;          /* Speed of bus in Khz */
         u16                     cmd_err;
         u8                      *buf;
@@ -603,8 +607,12 @@ 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.
          */
+        if (dev->set_mpu_wkup_lat != NULL)
+                dev->set_mpu_wkup_lat(dev->dev, dev->latency);
         r = wait_for_completion_timeout(&dev->cmd_complete,
                                         OMAP_I2C_TIMEOUT);
+        if (dev->set_mpu_wkup_lat != NULL)
+                dev->set_mpu_wkup_lat(dev->dev, -1);
         dev->buf_len = 0;
         if (r < 0)
                 return r;
@@ -927,6 +935,7 @@ 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;
@@ -956,10 +965,13 @@ 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;
@@ -1011,6 +1023,10 @@ omap_i2c_probe(struct platform_device *pdev)
                         dev->fifo_size = (dev->fifo_size / 2);
                         dev->b_hw = 1; /* Enable hardware fixes */
                 }
+                /* calculate wakeup latency constraint for MPU */
+                if (dev->set_mpu_wkup_lat != NULL)
+                        dev->latency = (1000000 * dev->fifo_size) /
+                                       (1000 * speed / 8);
         }
 
         /* reset ASAP, clearing any IRQs */