backlight: make the display backlight controllable via the broker framework

This allows changing the display brightness via the API and provides the
ground work to allow dimming of the backlight in the screensaver.

Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>

Author: hnez

openapi.yaml

@@ -41,6 +41,30 @@ paths:
               schema:
                 $ref: '#/components/schemas/Alerts'
 
+  /v1/tac/display/backlight/brightness:
+    get:
+      summary: Get the current backlight brightness (between 0.0, and 1.0)
+      tags: [User Interface]
+      responses:
+        '200':
+          content:
+            application/json:
+              schema:
+                type: number
+    put:
+      summary: Set the current backlight brightness (between 0.0 and 1.0)
+      tags: [User Interface]
+      requestBody:
+        content:
+          application/json:
+            schema:
+              type: number
+      responses:
+        '204':
+          description: The display brightness was set sucessfully
+        '400':
+          description: The value could not be parsed as a number
+
   /v1/tac/display/buttons:
     put:
       summary: Simulate a button press/release on the device

src/backlight.rs

@@ -0,0 +1,67 @@
+// This file is part of tacd, the LXA TAC system daemon
+// Copyright (C) 2023 Pengutronix e.K.
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+use anyhow::Result;
+use async_std::prelude::*;
+use async_std::sync::Arc;
+use async_std::task::spawn;
+use log::warn;
+
+mod demo_mode;
+
+#[cfg(feature = "demo_mode")]
+use demo_mode::{Backlight as SysBacklight, Brightness, SysClass};
+
+#[cfg(not(feature = "demo_mode"))]
+use sysfs_class::{Backlight as SysBacklight, Brightness, SysClass};
+
+use crate::broker::{BrokerBuilder, Topic};
+
+pub struct Backlight {
+    pub brightness: Arc<Topic<f32>>,
+}
+
+impl Backlight {
+    pub fn new(bb: &mut BrokerBuilder) -> Result<Self> {
+        let brightness = bb.topic_rw("/v1/tac/display/backlight/brightness", Some(1.0));
+
+        let (mut rx, _) = brightness.clone().subscribe_unbounded();
+
+        let backlight = SysBacklight::new("backlight")?;
+        let max_brightness = backlight.max_brightness()?;
+
+        spawn(async move {
+            while let Some(fraction) = rx.next().await {
+                let brightness = (max_brightness as f32) * fraction;
+                let mut brightness = brightness.clamp(0.0, max_brightness as f32) as u64;
+
+                // A brightness of 0 turns the backlight off completely.
+                // If the user selects something low but not zero they likely
+                // want a dim glow, not completely off.
+                if fraction > 0.01 && brightness == 0 {
+                    brightness = 1;
+                }
+
+                if let Err(e) = backlight.set_brightness(brightness) {
+                    warn!("Failed to set LED pattern: {}", e);
+                }
+            }
+        });
+
+        Ok(Self { brightness })
+    }
+}

src/backlight/demo_mode.rs

@@ -0,0 +1,90 @@
+// This file is part of tacd, the LXA TAC system daemon
+// Copyright (C) 2023 Pengutronix e.K.
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+use std::io::{Error, ErrorKind, Result};
+use std::path::{Path, PathBuf};
+use std::str::{from_utf8, FromStr};
+
+use sysfs_class::{set_trait_method, trait_method};
+
+pub trait SysClass: Sized {
+    fn class() -> &'static str;
+    unsafe fn from_path_unchecked(path: PathBuf) -> Self;
+    fn path(&self) -> &Path;
+
+    fn new(id: &str) -> Result<Self> {
+        let inst = unsafe { Self::from_path_unchecked(id.into()) };
+        Ok(inst)
+    }
+
+    fn read_file<P: AsRef<Path>>(&self, name: P) -> Result<String> {
+        let path = self.path().join(name);
+        let path = path.to_str().unwrap();
+
+        if path == "backlight/max_brightness" {
+            Ok("8".to_string())
+        } else {
+            Err(Error::new(ErrorKind::NotFound, format!("{path} not found")))
+        }
+    }
+
+    fn parse_file<F: FromStr, P: AsRef<Path>>(&self, name: P) -> Result<F> {
+        self.read_file(name)?
+            .parse()
+            .map_err(|_| Error::new(ErrorKind::InvalidData, "too bad"))
+    }
+
+    fn write_file<P: AsRef<Path>, S: AsRef<[u8]>>(&self, name: P, data: S) -> Result<()> {
+        let path = self.path().join(name);
+        let path = path.to_str().unwrap();
+        let data = from_utf8(data.as_ref()).unwrap();
+
+        log::info!("Backlight: Write {} to {}", data, path);
+
+        Ok(())
+    }
+}
+
+pub trait Brightness {
+    fn brightness(&self) -> Result<u64>;
+    fn max_brightness(&self) -> Result<u64>;
+    fn set_brightness(&self, val: u64) -> Result<()>;
+}
+
+pub struct Backlight {
+    path: PathBuf,
+}
+
+impl SysClass for Backlight {
+    fn class() -> &'static str {
+        "backlight"
+    }
+
+    unsafe fn from_path_unchecked(path: PathBuf) -> Self {
+        Self { path }
+    }
+
+    fn path(&self) -> &Path {
+        &self.path
+    }
+}
+
+impl Brightness for Backlight {
+    trait_method!(brightness parse_file u64);
+    trait_method!(max_brightness parse_file u64);
+    set_trait_method!("brightness", set_brightness u64);
+}

src/main.rs

@@ -18,6 +18,7 @@
 use futures::{select, FutureExt};
 
 mod adc;
+mod backlight;
 mod broker;
 mod dbus;
 mod digital_io;
@@ -36,6 +37,7 @@ mod usb_hub;
 mod watchdog;
 
 use adc::Adc;
+use backlight::Backlight;
 use broker::BrokerBuilder;
 use dbus::DbusSession;
 use digital_io::DigitalIo;
@@ -64,6 +66,7 @@ async fn main() -> Result<(), std::io::Error> {
     let mut bb = BrokerBuilder::new();
 
     // Expose hardware on the TAC via the broker framework.
+    let backlight = Backlight::new(&mut bb).unwrap();
     let led = Led::new(&mut bb);
     let adc = Adc::new(&mut bb).await.unwrap();
     let dut_pwr = DutPwrThread::new(
@@ -117,6 +120,7 @@ async fn main() -> Result<(), std::io::Error> {
     let ui = {
         let resources = UiResources {
             adc,
+            backlight,
             dig_io,
             dut_pwr,
             iobus,

src/ui.rs

@@ -39,6 +39,7 @@ use screens::{splash, ActivatableScreen, AlertScreen, NormalScreen, Screen};
 
 pub struct UiResources {
     pub adc: crate::adc::Adc,
+    pub backlight: crate::backlight::Backlight,
     pub dig_io: crate::digital_io::DigitalIo,
     pub dut_pwr: crate::dut_power::DutPwrThread,
     pub iobus: crate::iobus::IoBus,