Differences

This shows you the differences between two versions of the page.

--- litesom:devicetree:lcd [2017/02/14 20:40]
filug [Backlight]
+++ litesom:devicetree:lcd [2017/08/17 11:04]
filug [liteSOM and LCD display]
@@ Line 1: / Line 1: @@
-====== i.MX6UL and LCD display ======
+====== liteSOM and LCD display ======
+<well>
+{{:github-mark-32px.png?nolink |}}
+Example available on [[https://github.com/grinn-pub/examples|GitHub]].
+Check [[https://github.com/grinn-pub/examples/blob/master/configs/grinn_liteboard_lcd_res_defconfig|liteboard LCD + touchscreen]].
+</well>
 <columns 100% 50% - ->
@@ Line 37: / Line 44: @@
   * ''PWM'' - <tooltip title="to control LCD display backlight">Pulse Width Modulation</tooltip>.
-Below you can see how to configure [[litesom:liteboard]] to support [[emv:lcd]] module.
+Below you can see how to configure [[litesom:liteboard]] to support [[devices:lcd]] module.
-<alert type="info">Complete example for [[litesom:liteboard]] and [[emv:lcd]] you can find on our [[https://github.com/grinn-pub/examples|GitHub examples repository]].</alert>
+<alert type="info">Complete example for [[litesom:liteboard]] and [[devices:lcd]] you can find on our [[https://github.com/grinn-pub/examples|GitHub examples repository]].</alert>
 On [[evm:lcd]] we are using [[https://riverdi.com/product/rvt7-0a800480tnwr00/|RVT7.0A800480TNWR00]] TFT display produced by [[https://riverdi.com/|Riverdi]]. Below you can find short details about this device:
@@ Line 245: / Line 252: @@
 <uml>
 package "liteboard" {
-[Backlight driver] -> [PWM]
+[PWM backlight driver] -> [PWM]
 }
 package "Display" {
@@ Line 251: / Line 258: @@
 }
 </uml>
+<code>
+/ {
+  backlight {
+    compatible = "pwm-backlight";
+    pwms = <&pwm2 0 5000000>;
+    brightness-levels = <0 4 8 16 32 64 128 255>;
+    default-brightness-level = <6>;
+    status = "okay";
+  };
+};
+&iomuxc {
+  pinctrl_pwm2: pwm2 {
+    fsl,pins = <
+      MX6UL_PAD_GPIO1_IO09__PWM2_OUT   0x110b0
+    >;
+  };
+};
+&pwm2 {
+  pinctrl-names = "default";
+  pinctrl-0 = <&pinctrl_pwm2>;
+  status = "okay";
+  clocks = <&clks IMX6UL_CLK_PWM2>,
+           <&clks IMX6UL_CLK_PWM2>;
+};
+</code>
 <newcolumn>
-On [[litesom:liteboard]]
+On [[litesom:liteboard]] you can find dedicated LCD backlight boot converter (see [[http://www.ti.com/product/TPS61042|TPS61042]]) controlled by [[:litesom]] via ''PWM2 output'' pin.
-To drive ''LCD backlight'' at [[evm:lcd]] we can use //Pulse Width Modulation// peripheral from ''i.MX6UL''.
+{{ :litesom:devicetree:litesom_backlight_driver.png?500 |}}
+Backlight can be controlled directly via ''PWM driver'' but additional ''PWM backlight driver'' will <tooltip title="from software point of view">simplify</tooltip> backlight configuration.
+Node ''backlight'' is documented in [[https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt|pwm-backlight.txt]] file.
+Backlight configured as presented here will:
+  * generate PWM with 200Hz frequency (period 5000000 ns),
+  * use ''PWM2'' peripheral as backlight controller,
+  * define eight allowed backlight levels: 0%, 2%, 3%, 6%, 13%, 25%, 50%, 100%,
+  * use 50% as default backlight level.
+Node ''pinctrl_pwm2'' is information for ''IOMUX controller'' how to configure ''PWM2'' output. On [[litesom:liteboard]] we are using ''GPIO1__IO09''.
+{{ :litesom:devicetree:litesom_backlight.png?400 |}}
+Node ''pwm2'' is configured as documented in [[https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/pwm/pwm.txt|pwm.txt]].
 </columns>