linux-kernel - Re: [PATCH V8 6/6] backlight: qcom-wled: Add auto string detection logic

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Date:   Mon, 21 Oct 2019 11:31:50 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Kiran Gunda <kgunda@...eaurora.org>
Cc:     bjorn.andersson@...aro.org, jingoohan1@...il.com,
        lee.jones@...aro.org, b.zolnierkie@...sung.com,
        dri-devel@...ts.freedesktop.org, jacek.anaszewski@...il.com,
        pavel@....cz, robh+dt@...nel.org, mark.rutland@....com,
        linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH V8 6/6] backlight: qcom-wled: Add auto string detection
 logic

On Fri, Oct 18, 2019 at 06:03:29PM +0530, Kiran Gunda wrote:
> The auto string detection algorithm checks if the current WLED
> sink configuration is valid. It tries enabling every sink and
> checks if the OVP fault is observed. Based on this information
> it detects and enables the valid sink configuration.
> Auto calibration will be triggered when the OVP fault interrupts
> are seen frequently thereby it tries to fix the sink configuration.
> 
> The auto-detection also kicks in when the connected LED string
> of the display-backlight malfunctions (because of damage) and
> requires the damaged string to be turned off to prevent the
> complete panel and/or board from being damaged.
> 
> Signed-off-by: Kiran Gunda <kgunda@...eaurora.org>
> ---
>  drivers/video/backlight/qcom-wled.c | 398 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 392 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> index 658b1e0..b2e6754 100644
> --- a/drivers/video/backlight/qcom-wled.c
> +++ b/drivers/video/backlight/qcom-wled.c
> @@ -193,7 +216,23 @@ static int wled_module_enable(struct wled *wled, int val)
>  				WLED3_CTRL_REG_MOD_EN,
>  				WLED3_CTRL_REG_MOD_EN_MASK,
>  				val << WLED3_CTRL_REG_MOD_EN_SHIFT);
> -	return rc;
> +	if (rc < 0)
> +		return rc;
> +
> +	if (wled->ovp_irq > 0) {
> +		if (val) {
> +			/*
> +			 * Wait for at least 10ms before enabling OVP interrupt
> +			 * after module enable so that soft start is completed.
> +			 */

Comments should not say what is does (we can read that). It should be
saying what is weird about the hardware the results in us enabling the
interrupt in an unusual way.

More like:

"The hardware generates a storm of spurious OVP interrupts during soft
start operations so defer enabling the IRQ for 10ms to ensure that
the soft start is complete."

Note that I am only guessing that is an spurious interrupt storm that
caused you to defer the interrupt enable... I don't want to have to
guess which is why I am asking for a good quality comment!


Daniel.