linux-kernel - Re: [PATCH 2/3] pwm: New driver to support PWMs on TWL4030/6030 series of PMICs

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Date:	Thu, 8 Nov 2012 08:14:36 +0100
From:	Péter Ujfalusi <peter.ujfalusi@...com>
To:	Grazvydas Ignotas <notasas@...il.com>
CC:	Thierry Reding <thierry.reding@...onic-design.de>,
	Tero Kristo <t-kristo@...com>, <linux-kernel@...r.kernel.org>,
	<linux-omap@...r.kernel.org>
Subject: Re: [PATCH 2/3] pwm: New driver to support PWMs on TWL4030/6030 series
 of PMICs

On 11/07/2012 06:50 PM, Grazvydas Ignotas wrote:
>> +static int twl4030_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
>> +{
>> +       int ret;
>> +       u8 val;
>> +
>> +       ret = twl_i2c_read_u8(TWL4030_MODULE_INTBR, &val, TWL4030_GPBR1_REG);
>> +       if (ret < 0) {
>> +               dev_err(chip->dev, "%s: Failed to read GPBR1\n", pwm->label);
>> +               return ret;
>> +       }
>> +
>> +       val |= TWL4030_PWM_TOGGLE(pwm->hwpwm, TWL4030_PWMX_BITS);
> 
> In my experience doing it like this doesn't work reliably, i.e.
> sometimes it just won't enable. I had to first set CLK_ENABLE bit, and
> then ENABLE bit with separate i2c write. Perhaps it needs a cycle or
> two of 32k clock or something (that doesn't seem to be documented
> though).

Thanks, I'll change to the reliable sequence. I do not have HW where I can
test the twl4030 PWMs.

> 
>> +
>> +       ret = twl_i2c_write_u8(TWL4030_MODULE_INTBR, val, TWL4030_GPBR1_REG);
>> +       if (ret < 0)
>> +               dev_err(chip->dev, "%s: Failed to enable PWM\n", pwm->label);
>> +
>> +       return ret;
>> +}
>> +
>> +static void twl4030_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>> +{
>> +       int ret;
>> +       u8 val;
>> +
>> +       ret = twl_i2c_read_u8(TWL4030_MODULE_INTBR, &val, TWL4030_GPBR1_REG);
>> +       if (ret < 0) {
>> +               dev_err(chip->dev, "%s: Failed to read GPBR1\n", pwm->label);
>> +               return;
>> +       }
>> +
>> +       val &= ~TWL4030_PWM_TOGGLE(pwm->hwpwm, TWL4030_PWMX_BITS);
> 
> Same problem here, I would sometimes get LED stuck at full brightness
> after this, first clearing ENABLE and then CLK_ENABLE fixed it (we
> have charger LED connected to PWM1 on pandora).

I would guessed that if we need special care we should have turned off CLK
followed by disabling the PWM.
I'll use the sequence you described in the next version.

> 
>> +
>> +       ret = twl_i2c_write_u8(TWL4030_MODULE_INTBR, val, TWL4030_GPBR1_REG);
>> +       if (ret < 0)
>> +               dev_err(chip->dev, "%s: Failed to disable PWM\n", pwm->label);
>> +}
>> +
>> +static int twl4030_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
>> +{
>> +       struct twl_pwm_chip *twl = container_of(chip, struct twl_pwm_chip,
>> +                                               chip);
>> +       int ret;
>> +       u8 val, mask, bits;
>> +
>> +       ret = twl_i2c_read_u8(TWL4030_MODULE_INTBR, &val, TWL4030_PMBR1_REG);
>> +       if (ret < 0) {
>> +               dev_err(chip->dev, "%s: Failed to read PMBR1\n", pwm->label);
>> +               return ret;
>> +       }
>> +
>> +       if (pwm->hwpwm) {
>> +               /* PWM 1 */
>> +               mask = TWL4030_GPIO7_VIBRASYNC_PWM1_MASK;
>> +               bits = TWL4030_GPIO7_VIBRASYNC_PWM1_PWM1;
>> +       } else {
>> +               /* PWM 0 */
>> +               mask = TWL4030_GPIO6_PWM0_MUTE_MASK;
>> +               bits = TWL4030_GPIO6_PWM0_MUTE_PWM0;
>> +       }
>> +
>> +       /* Save the current MUX configuration for the PWM */
>> +       twl->twl4030_pwm_mux &= ~mask;
>> +       twl->twl4030_pwm_mux |= (val & mask);
> 
> Do we really need this mask clearing here? After probe twl4030_pwm_mux
> should be zero, and if twl4030_pwm_request is called twice you don't
> clear the important bits before |=, I think 'twl4030_pwm_mux = val &
> mask' would be better here.

I'm storing both PWM's state in the same variable, but in different offsets:
PWM0: bits 2-3
PWM1: bits 4-5
Probably it is over engineering to clear the relevant bits in the backup
storage, but better to be safe IMHO.
I would leave this part as it is.

-- 
Péter
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