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Date:	Fri, 11 Jul 2014 15:07:33 +0530
From:	amit daniel kachhap <amit.daniel@...sung.com>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Cc:	Lee Jones <lee.jones@...aro.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Mike Turquette <mturquette@...aro.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	devicetree@...r.kernel.org,
	Yadwinder Singh Brar <yadi.brar01@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Doug Anderson <dianders@...omium.org>,
	Tushar Behera <trblinux@...il.com>,
	Mark Brown <broonie@...nel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Olof Johansson <olof@...om.net>,
	Andreas Farber <afaerber@...e.de>,
	LAK <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 08/24] mfd: max77686: Add Dynamic Voltage Scaling (DVS) support

On Fri, Jul 11, 2014 at 7:15 AM, Javier Martinez Canillas
<javier.martinez@...labora.co.uk> wrote:
> 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
>> <javier.martinez@...labora.co.uk> wrote:
>>> 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 <amit.daniel@...sung.com>
>>
>
> Thanks.
>
>>>
>>> Signed-off-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
>>> Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
>>> ---
>>>
>>> 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.
Hmm its fine then.
>
> AFAIU the only thing that the kernel should check is if a required property does
> not exist.
>
>>> +
>>> +       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.
Agreed DVS functionality can be added later.
>
>>> +       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
>
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