add width and height support (hack)

4 files changed, 64 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
index f673b77..4bd4096 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,3 +7,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+byteorder = "1.*"
diff --git a/examples/width_height.rs b/examples/width_height.rs
new file mode 100644
index 0000000..77bb5da
--- /dev/null
+++ b/examples/width_height.rs
@@ -0,0 +1,12 @@
+use charlcd::Screen;
+use std::io::Write;
+
+fn main() -> std::io::Result<()> {
+    let mut screen = Screen::default()?;
+
+    screen.clear()?;
+    screen.write(format!("width: {}\n", screen.width()?).as_bytes())?;
+    screen.write(format!("height: {}\n", screen.height()?).as_bytes())?;
+
+    Ok(())
+}
diff --git a/src/lib.rs b/src/lib.rs
index f849712..0e32ee9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,5 @@
 mod codes;
+mod of_node;
 
 use std::fs::{File, OpenOptions};
 use std::path::Path;
@@ -198,4 +199,30 @@ impl FileScreen {
     pub fn default() -> std::io::Result<FileScreen> {
         Screen::from_dev_path(&Path::new(DEFAULT_SCREEN_DEV_PATH))
     }
+
+    /// Get the width of the screen, in number of characters it can display.
+    ///
+    /// **Important note:** The implementation behind this function is
+    /// currently a hack that will go find the value in the `auxdisplay`
+    /// platform device tree node in
+    /// `/sys/devices/platform/auxdisplay/of_node/*`. This is because the
+    /// `charlcd` driver does not export the screen width nor height to
+    /// userspace (could be using `ioctl` or `read` syscalls).
+    ///
+    pub fn width(&self) -> std::io::Result<u32> {
+        of_node::display_width_chars()
+    }
+
+    /// Get the height of the screen, in number of characters it can display.
+    ///
+    /// **Important note:** The implementation behind this function is
+    /// currently a hack that will go find the value in the `auxdisplay`
+    /// platform device tree node in
+    /// `/sys/devices/platform/auxdisplay/of_node/*`. This is because the
+    /// `charlcd` driver does not export the screen width nor height to
+    /// userspace (could be using `ioctl` or `read` syscalls).
+    ///
+    pub fn height(&self) -> std::io::Result<u32> {
+        of_node::display_height_chars()
+    }
 }
diff --git a/src/of_node.rs b/src/of_node.rs
new file mode 100644
index 0000000..5dff2a0
--- /dev/null
+++ b/src/of_node.rs
@@ -0,0 +1,24 @@
+// This module is a hack to read additional information in the DT nodes in the
+// kernel to retrieve data that is currently not exposed in the charlcd.c
+// driver.
+
+use std::fs::File;
+use std::io::Result;
+
+use byteorder::{BigEndian, ReadBytesExt};
+
+fn read_u32_node(node_name: &str) -> Result<u32> {
+    let mut f = File::open(format!(
+        "/sys/devices/platform/auxdisplay/of_node/{}",
+        node_name
+    ))?;
+    Ok(f.read_u32::<BigEndian>()?)
+}
+
+pub fn display_height_chars() -> Result<u32> {
+    read_u32_node("display-height-chars")
+}
+
+pub fn display_width_chars() -> Result<u32> {
+    read_u32_node("display-width-chars")
+}