Re: [PATCH v7 08/24] mfd: max77686: Add Dynamic Voltage Scaling (DVS) support

Hello Amit,

On 07/10/2014 11:59 AM, amit daniel kachhap wrote:

On Sat, Jul 5, 2014 at 1:54 AM, Javier Martinez Canillas
[off-list ref] wrote:

quoted

Some regulators on the MAX77686 PMIC have Dynamic Voltage Scaling
(DVS) support that allows output voltage to change dynamically.

For MAX77686, these regulators are Buck regulators 2, 3 and 4.

Each Buck output voltage is selected using a set of external
inputs: DVS1-3 and SELB2-4.

DVS registers can be used to configure the output voltages for each
Buck regulator and which one is active is controled by DVSx lines.

SELBx lines are used to control if individual Buck lines are ON or OFF.

This patch adds support to configure the DVSx and SELBx lines
from DT and to setup and read the GPIO lines connected to them.

The entire series looks nice. Few minor comments from my side. I guess
still one more version in needed as per other ppls comment.
You may add,
Reviewed-by: Amit Daniel Kachhap <redacted>

Thanks.

quoted

Signed-off-by: Javier Martinez Canillas <redacted>
Reviewed-by: Krzysztof Kozlowski <redacted>
---

Changes since v6:
 - Add a comment that max77686_read_gpios() function can sleep.
   Sugggested by Krzysztof Kozlowski
---
 drivers/mfd/max77686.c       | 119 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/max77686.h |  18 ++++---
 2 files changed, 129 insertions(+), 8 deletions(-)

diff --git a/drivers/mfd/max77686.c b/drivers/mfd/max77686.c
index 8650832..d193873 100644
--- a/drivers/mfd/max77686.c
+++ b/drivers/mfd/max77686.c

@@ -32,8 +32,10 @@
 #include <linux/mfd/core.h>
 #include <linux/mfd/max77686.h>
 #include <linux/mfd/max77686-private.h>
+#include <linux/gpio/consumer.h>
 #include <linux/err.h>
 #include <linux/of.h>
+#include <linux/export.h>

 #define I2C_ADDR_RTC   (0x0C >> 1)

@@ -101,9 +103,119 @@ static const struct of_device_id max77686_pmic_dt_match[] = {
        {},
 };

+static void max77686_dt_parse_dvs_gpio(struct device *dev)
+{
+       struct max77686_platform_data *pd = dev_get_platdata(dev);
+       int i;
+
+       /*
+        * NOTE: we don't consider GPIO errors fatal; board may have some lines
+        * directly pulled high or low and thus doesn't specify them.
+        */
+       for (i = 0; i < ARRAY_SIZE(pd->buck_gpio_dvs); i++)
+               pd->buck_gpio_dvs[i] =
+                       devm_gpiod_get_index(dev, "max77686,pmic-buck-dvs", i);
+
+       for (i = 0; i < ARRAY_SIZE(pd->buck_gpio_selb); i++)
+               pd->buck_gpio_selb[i] =
+                       devm_gpiod_get_index(dev, "max77686,pmic-buck-selb", i);
+}
+
+/**
+ * max77686_setup_gpios() - init DVS-related GPIOs
+ * @dev: device whose platform data contains the dvs GPIOs information
+ *
+ * This function claims / initalizations GPIOs related to DVS if they are
+ * defined. This may have the effect of switching voltages if the
+ * pdata->buck_default_idx does not match the boot time state of pins.
+ */
+int max77686_setup_gpios(struct device *dev)
+{
+       struct max77686_platform_data *pd = dev_get_platdata(dev);
+       int buck_default_idx = pd->buck_default_idx;
+       int ret;
+       int i;
+
+       /* Set all SELB high to avoid glitching while DVS is changing */
+       for (i = 0; i < ARRAY_SIZE(pd->buck_gpio_selb); i++) {
+               struct gpio_desc *gpio = pd->buck_gpio_selb[i];
+
+               /* OK if some GPIOs aren't defined */
+               if (IS_ERR(gpio))
+                       continue;
+
+               ret = gpiod_direction_output_raw(gpio, 1);
+               if (ret) {
+                       dev_err(dev, "can't set gpio[%d] dir: %d\n", i, ret);
+                       return ret;
+               }
+       }
+
+       /* Set our initial setting */
+       for (i = 0; i < ARRAY_SIZE(pd->buck_gpio_dvs); i++) {
+               struct gpio_desc *gpio = pd->buck_gpio_dvs[i];
+
+               /* OK if some GPIOs aren't defined */
+               if (IS_ERR(gpio))
+                       continue;
+
+               /* If a GPIO is valid, set it */
+               gpiod_direction_output(gpio, (buck_default_idx >> i) & 1);
+               if (ret) {
+                       dev_err(dev, "can't set gpio[%d]: dir %d\n", i, ret);
+                       return ret;
+               }
+       }
+
+       /* Now set SELB low to take effect */
+       for (i = 0; i < ARRAY_SIZE(pd->buck_gpio_selb); i++) {
+               struct gpio_desc *gpio = pd->buck_gpio_selb[i];
+
+               if (!IS_ERR(gpio))
+                       gpiod_set_value(gpio, 0);
+       }
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(max77686_setup_gpios);
+
+/**
+ * max77686_read_gpios() - read the current state of the dvs GPIOs
+ * @pdata: platform data that contains the dvs GPIOs information
+ *
+ * We call this function at bootup to detect what slot the firmware was
+ * using for the DVS GPIOs.  That way we can properly preserve the firmware's
+ * voltage settings
+ *
+ * This function can sleep so must not be called from atomic context.
+ */
+int max77686_read_gpios(struct max77686_platform_data *pdata)
+{
+       int buck_default_idx = pdata->buck_default_idx;
+       int result = 0;
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(pdata->buck_gpio_dvs); i++) {
+               struct gpio_desc *gpio = pdata->buck_gpio_dvs[i];
+
+               /* OK if some GPIOs aren't defined; we'll use default */
+               if (IS_ERR(gpio)) {
+                       result |= buck_default_idx & (1 << i);
+                       continue;
+               }
+
+               if (gpiod_get_value_cansleep(gpio))
+                       result |= 1 << i;
+       }
+
+       return result;
+}
+EXPORT_SYMBOL_GPL(max77686_read_gpios);
+
 static struct max77686_platform_data *max77686_i2c_parse_dt_pdata(struct device
                                                                  *dev)
 {
+       struct device_node *np = dev->of_node;
        struct max77686_platform_data *pd;

        pd = devm_kzalloc(dev, sizeof(*pd), GFP_KERNEL);

@@ -111,6 +223,13 @@ static struct max77686_platform_data *max77686_i2c_parse_dt_pdata(struct device
                return NULL;

        dev->platform_data = pd;
+
+       /* Read default index and ignore errors, since default is 0 */
+       of_property_read_u32(np, "max77686,pmic-buck-default-dvs-idx",
+                            &pd->buck_default_idx);

Any error checking code here. Say if pmic-buck-default-dvs-idx exceed 8?

I'm not a DT expert but AFAIK the kernel should expect the data in a FDT to be
correct and should not validate it on runtime. There is work-in-progress to add
a proper schema checking for DTS to the dtc so on build time it can be validated
that a DTS is valid.

AFAIU the only thing that the kernel should check is if a required property does
not exist.

quoted

+
+       max77686_dt_parse_dvs_gpio(dev);
+
        return pd;
 }

diff --git a/include/linux/mfd/max77686.h b/include/linux/mfd/max77686.h
index 4cbcc13..46a736b 100644
--- a/include/linux/mfd/max77686.h
+++ b/include/linux/mfd/max77686.h

@@ -99,15 +99,17 @@ struct max77686_platform_data {
        struct max77686_opmode_data *opmode_data;

        /*
-        * GPIO-DVS feature is not enabled with the current version of
-        * MAX77686 driver. Buck2/3/4_voltages[0] is used as the default
-        * voltage at probe. DVS/SELB gpios are set as OUTPUT-LOW.
+        * GPIO-DVS feature is not fully enabled with the current version of
+        * MAX77686 driver, but the driver does support using a DVS index other
+        * than the default of 0.
         */
-       int buck234_gpio_dvs[3]; /* GPIO of [0]DVS1, [1]DVS2, [2]DVS3 */
-       int buck234_gpio_selb[3]; /* [0]SELB2, [1]SELB3, [2]SELB4 */
-       unsigned int buck2_voltage[8]; /* buckx_voltage in uV */
-       unsigned int buck3_voltage[8];
-       unsigned int buck4_voltage[8];

I think when DVS gpio is used all the 8 voltage levels are fetched
from DT during booting and the registers are programmed accordingly.
Any further set/get_voltage just changes the GPIO lines.
Any reason why this method is not used?

What are you describing is how the DT binding works for other Maxim PMICs that
also have DVS support right? (e.g: max8997).

The DVS binding in max77686/802 is actually a subset of the one in max8997 so it
let's you only choose which single DVS index is going to be used. The GPIOs in
"max77686,pmic-buck-dvs-gpios" should match "pmic-buck-default-dvs-idx".

To be honest I just took the DT binding that was used in the max77xxx driver
from the Chrome OS 3.8 kernel and didn't compare it with other Maxim PMICs DT
bingings.

I wonder if I should just take the DVS patches out from this initial version to
avoid blocking the max77802 support and then we can discuss this in more detail.

quoted

+       struct gpio_desc *buck_gpio_dvs[3]; /* GPIO of [0]DVS1, [1]DVS2, [2]DVS3 */
+       int buck_default_idx; /* Default value of DVS1, 2, 3 */
+
+       struct gpio_desc *buck_gpio_selb[3]; /* Buck regulators 2, 3, 4 */
 };

+extern int max77686_setup_gpios(struct device *dev);
+extern int max77686_read_gpios(struct max77686_platform_data *pdata);
+
 #endif /* __LINUX_MFD_MAX77686_H */
--
2.0.0.rc2

Best regards,
Javier