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Message-ID: <bc1cda62-b82c-231f-fc38-27b752ecb7c6@ti.com>
Date: Tue, 1 Nov 2016 11:17:18 +0200
From: Peter Ujfalusi <peter.ujfalusi@...com>
To: Philipp Zabel <p.zabel@...gutronix.de>
CC: <thierry.reding@...il.com>, <lee.jones@...aro.org>,
<tomi.valkeinen@...com>, <linux-pwm@...r.kernel.org>,
<linux-fbdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] backlight: pwm_bl: Move the checks for initial
power state to a separate function
On 10/28/2016 04:27 PM, Philipp Zabel wrote:
> Hi Peter,
>
> Am Donnerstag, den 27.10.2016, 13:01 +0300 schrieb Peter Ujfalusi:
>> Move the checks to select the initial state for the backlight to a new
>> function and document the checks we are doing.
>>
>> At the same time correct the handling of the case when the GPIO is
>> initially configured as input: we need to change the direction of the GPIO
>> to output and set the GPIO to low as the pin was not driven when the GPIO
>> was configured as input.
>
> I think this part should be a separate patch. At least it is a
> significant enough change to warrant a mention in the subject.
Yes, I should have separated it it.
> And I'm not entirely sure this is better than before. If there happens
> to be a pull-up on the GPIO (for whatever reason), we might introduce
> flicker again if the GPIO goes from input (high) to output (low), and
> back to output (high) again due to FB_BLANK_UNBLANK.
This is plausible if the pull-up is strong enough. It might be better to
not change this logic at all and instead of gpiod_direction_output_raw()
use the gpiod_direction_output(pb->enable_gpio, 1); to enable the GPIO
when it is set as input.
I'll resend the patches.
--
Péter
> regards
> Philipp
>
>> With the separate function it is going to be easier to fix or improve the
>> initial power state configuration later and it is easier to read the code.
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
>> ---
>> drivers/video/backlight/pwm_bl.c | 54 ++++++++++++++++++++++++++--------------
>> 1 file changed, 35 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
>> index 12614006211e..74083d880144 100644
>> --- a/drivers/video/backlight/pwm_bl.c
>> +++ b/drivers/video/backlight/pwm_bl.c
>> @@ -192,6 +192,32 @@ static int pwm_backlight_parse_dt(struct device *dev,
>> }
>> #endif
>>
>> +static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
>> +{
>> + struct device_node *node = pb->dev->of_node;
>> +
>> + /* Not booted with device tree or no phandle link to the node */
>> + if (!node || !node->phandle)
>> + return FB_BLANK_UNBLANK;
>> +
>> + /*
>> + * If the driver is probed from the device tree and there is a
>> + * phandle link pointing to the backlight node, it is safe to
>> + * assume that another driver will enable the backlight at the
>> + * appropriate time. Therefore, if it is disabled, keep it so.
>> + */
>> +
>> + /* if the enable GPIO is disabled, do not enable the backlight */
>
> nitpick: s/if/If/ for consistency.
>
>> + if (pb->enable_gpio && gpiod_get_value(pb->enable_gpio) == 0)
>> + return FB_BLANK_POWERDOWN;
>> +
>> + /* The regulator is disabled, do not enable the backlight */
>> + if (!regulator_is_enabled(pb->power_supply))
>> + return FB_BLANK_POWERDOWN;
>> +
>> + return FB_BLANK_UNBLANK;
>> +}
>> +
>> static int pwm_backlight_probe(struct platform_device *pdev)
>> {
>> struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
>> @@ -200,7 +226,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>> struct backlight_device *bl;
>> struct device_node *node = pdev->dev.of_node;
>> struct pwm_bl_data *pb;
>> - int initial_blank = FB_BLANK_UNBLANK;
>> struct pwm_args pargs;
>> int ret;
>>
>> @@ -267,20 +292,14 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>> pb->enable_gpio = gpio_to_desc(data->enable_gpio);
>> }
>>
>> - if (pb->enable_gpio) {
>> - /*
>> - * If the driver is probed from the device tree and there is a
>> - * phandle link pointing to the backlight node, it is safe to
>> - * assume that another driver will enable the backlight at the
>> - * appropriate time. Therefore, if it is disabled, keep it so.
>> - */
>> - if (node && node->phandle &&
>> - gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT &&
>> - gpiod_get_value(pb->enable_gpio) == 0)
>> - initial_blank = FB_BLANK_POWERDOWN;
>> - else
>> - gpiod_direction_output(pb->enable_gpio, 1);
>> - }
>> + /*
>> + * If the GPIO is configured as input, change the direction to output
>> + * and set the GPIO as low since the line was not driven when it was
>> + * configured as input.
>> + */
>> + if (pb->enable_gpio &&
>> + gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_IN)
>> + gpiod_direction_output_raw(pb->enable_gpio, 0);
>>
>> pb->power_supply = devm_regulator_get(&pdev->dev, "power");
>> if (IS_ERR(pb->power_supply)) {
>> @@ -288,9 +307,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>> goto err_alloc;
>> }
>>
>> - if (node && node->phandle && !regulator_is_enabled(pb->power_supply))
>> - initial_blank = FB_BLANK_POWERDOWN;
>> -
>> pb->pwm = devm_pwm_get(&pdev->dev, NULL);
>> if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) {
>> dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
>> @@ -347,7 +363,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>> }
>>
>> bl->props.brightness = data->dft_brightness;
>> - bl->props.power = initial_blank;
>> + bl->props.power = pwm_backlight_initial_power_state(pb);
>> backlight_update_status(bl);
>>
>> platform_set_drvdata(pdev, bl);
>
>
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