linux-kernel - Re: [PATCH v2 1/2] leds: flash: leds-qcom-flash: update torch current clamp setting

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Message-ID: <f3c004a9-dba9-48b5-9930-979053d0a32c@oss.qualcomm.com>
Date: Tue, 29 Jul 2025 13:01:31 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: fenglin.wu@....qualcomm.com, kernel@....qualcomm.com,
        Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>
Cc: Subbaraman Narayanamurthy <subbaraman.narayanamurthy@....qualcomm.com>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] leds: flash: leds-qcom-flash: update torch current
 clamp setting

On 7/29/25 6:51 AM, Fenglin Wu via B4 Relay wrote:
> From: Fenglin Wu <fenglin.wu@....qualcomm.com>
> 
> There is a register to clamp the flash current per LED channel when
> safety timer is disabled. It needs to be updated according to the
> maximum torch LED current setting to ensure the torch current won't
> be clamped unexpectedly.
> 
> Fixes: 96a2e242a5dc ("leds: flash: Add driver to support flash LED module in QCOM PMICs")
> Signed-off-by: Fenglin Wu <fenglin.wu@....qualcomm.com>
> ---

I'd prefer the regfield change was done in a separate commit,
but it's not groundbreaking so I don't mind that much

[...]

>  struct qcom_flash_led {
> @@ -702,6 +706,7 @@ static int qcom_flash_register_led_device(struct device *dev,
>  	u32 current_ua, timeout_us;
>  	u32 channels[4];
>  	int i, rc, count;
> +	u8 torch_clamp;
>  
>  	count = fwnode_property_count_u32(node, "led-sources");
>  	if (count <= 0) {
> @@ -751,6 +756,12 @@ static int qcom_flash_register_led_device(struct device *dev,
>  	current_ua = min_t(u32, current_ua, TORCH_CURRENT_MAX_UA * led->chan_count);
>  	led->max_torch_current_ma = current_ua / UA_PER_MA;
>  
> +	torch_clamp = (current_ua / led->chan_count) / TORCH_IRES_UA;
> +	if (torch_clamp != 0)
> +		torch_clamp--;
> +
> +	flash_data->torch_clamp = max_t(u8, flash_data->torch_clamp, torch_clamp);

Please confirm if I understand correctly, we may have N flash LEDs 
connected, and this additional safety hardware can only compare any
individual LED's current draw against a single maximum value, which
we're setting here

Konrad