linux-kernel - Re: [RFC PATCH] leds: add sgm3140 driver

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Message-ID: <b58ddefc-b282-5a85-9dca-824e513705de@gmail.com>
Date:   Sun, 8 Mar 2020 17:47:17 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Luca Weiss <luca@...tu.xyz>, linux-leds@...r.kernel.org
Cc:     ~postmarketos/upstreaming@...ts.sr.ht, Pavel Machek <pavel@....cz>,
        Dan Murphy <dmurphy@...com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] leds: add sgm3140 driver

Hi Luca,

On 3/8/20 12:32 PM, Luca Weiss wrote:
> Hi Jacek,
> 
> Thanks for your review! Replies are inline below.
> 
> I'm wondering if I should implement support for the flash-max-timeout-us dt 
> property ("Maximum timeout in microseconds after which the flash LED is turned 
> off.") to configure the timeout to turn the flash off as I've currently hardcoded 
> 250ms but this might not be ideal for all uses of the sgm3140. The datasheet 
> states:
> 
>> Flash mode is usually used with a pulse of about 200 to 300 milliseconds to 
>> generate a high intensity Flash.
> 
> so it might be useful to have this configurable in the devicetree. The value of 
> 250ms works fine for my use case.

Yeah, I was to mentioned that.

> 
> Theoretically also the .timeout_set op could be implemented but I'm not sure 
> if this fits nicely into the existing "timeout" API and if it even makes sense 
> to implement that.

Why wouldn't it fit? You can implement timeout_set op and cache flash
timeout value in it. Then that cached value would be passed in
strobe_set to mod_timer() in place of currently hard coded 250.

> 
> Regards,
> Luca
> 
> On Donnerstag, 5. März 2020 22:09:16 CET Jacek Anaszewski wrote:
>> Hi Luca,
>>
>> Thank you for the patch.
>>
>> On 2/27/20 7:50 PM, Luca Weiss wrote:
>>> Add a driver for the SGMICRO SGM3140 Buck/Boost Charge Pump LED driver.
>>>
>>> This device is controller by two GPIO lines, one for enabling the LED
>>> and the second one for switching between torch and flash mode.
>>>
>>> The device will automatically switch to torch mode after being in flash
>>> mode for about 250-300ms, so after that time the driver will turn the
>>> LED off again automatically.
>>>
>>> Signed-off-by: Luca Weiss <luca@...tu.xyz>
>>> ---
>>> Hi, this driver is controllable via sysfs and v4l2 APIs (as documented
>>> in Documentation/leds/leds-class-flash.rst).
>>>
>>> The following is possible:
>>>
>>> # Torch on
>>> echo 1 > /sys/class/leds/white\:flash/brightness
>>> # Torch off
>>> echo 0 > /sys/class/leds/white\:flash/brightness
>>> # Activate flash
>>> echo 1 > /sys/class/leds/white\:flash/flash_strobe
>>>
>>> # Torch on
>>> v4l2-ctl -d /dev/video1 -c led_mode=2
>>> # Torch off
>>> v4l2-ctl -d /dev/video1 -c led_mode=0
>>> # Activate flash
>>> v4l2-ctl -d /dev/video1 -c strobe=1
>>
>> What is /dev/video1 ? Did you register vl42 flash subdev
>> in some v4l2 media controller device?
> 
> On the Allwinner A64 SoC /dev/video0 is the node for cedrus (video encoder/
> decoder), so the sun6i-csi driver gets to be /dev/video1
> 
> # v4l2-ctl --list-devices
> cedrus (platform:cedrus):
>         /dev/video0
>         /dev/media0
> 
> sun6i-csi (platform:csi):
>         /dev/video1
> 
> Allwinner Video Capture Device (platform:sun6i-csi):
>         /dev/media1
> 
> 
> Here's the relevant part from my dts:
> 
> sgm3140 {
>     compatible = "sgmicro,sgm3140";
>     flash-gpios = <&pio 3 24 GPIO_ACTIVE_HIGH>; /* FLASH_TRIGOUT: PD24 */
>     enable-gpios = <&pio 2 3 GPIO_ACTIVE_HIGH>; /* FLASH_EN: PC3 */
> 
>     sgm3140_flash: led {
>         function = LED_FUNCTION_FLASH;
>         color = <LED_COLOR_ID_WHITE>;
>     };
> };

This needs to be documented in DT bindings for this driver.

> /* as subnode of csi (compatible: allwinner,sun50i-a64-csi) */
> ov5640: rear-camera@4c {
>     compatible = "ovti,ov5640";
>     <snip>
>     flash-leds = <&sgm3140_flash>;
> };

And this in camera bindings.

-- 
Best regards,
Jacek Anaszewski