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kernel: porting: Adapt the Crystalfontz DT description
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These changes rework the way the Crystalfontz board is being described before
maybe another board (64-bit) gets introduced:
- Instead of showing the raw content of its device tree written with a
  rather legacy syntax, I took the freedom to describe the nodes as I
  think they *should* be described with today's habits.
- The ordering is also updated and the way the nodes are presented
  contains the parent node when relevant in order to show how a device
  tree gets constructed more than how a device tree can be read.
- I also dropped the MMC description which did not bring anything useful
  to my eyes.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
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@miquelraynal @tpetazzoni
miquelraynal authored and tpetazzoni committed Oct 29, 2021
1 parent a69445e commit e18ea4b
Showing 1 changed file with 109 additions and 126 deletions.
235 changes: 109 additions & 126 deletions slides/kernel-porting-content/kernel-porting-content.tex
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\begin{frame}[fragile]
\frametitle{Crystalfontz CFA-10036 Device Tree, header}
\begin{itemize}
\item SPDX license tag\\
\item Mandatory Device Tree language definition\\
\begin{block}{} \mint[fontsize=\small]{perl}+/dts-v1/+ \end{block}
\begin{block}{} \mint[fontsize=\small]{perl}+/dts-v1/;+ \end{block}
\item Include the \code{.dtsi} file describing the SoC\\
\begin{block}{}
\mint[fontsize=\small]{perl}+#include "imx28.dtsi"+
\end{block}
\item Start the root of the tree\\
\begin{block}{} \mint[fontsize=\small]{perl}+/ {+ \end{block}
\item A human-readable string to describe the machine (shown at boot time)\\
\begin{block}{}
\mint[fontsize=\small]{perl}+model = "Crystalfontz CFA-10036 Board";+
\end{block}
\item A list of {\em compatible} strings, from the most specific one
to the most general one. Mandatory to execute the right SoC specific
initializations and board specific code.\\
\begin{block}{}
\mint[fontsize=\small]{perl}+compatible = "crystalfontz,cfa10036", "fsl,imx28";+
\end{block}
\item Start the root of the tree (named \code{/}) then describe the board
\begin{itemize}
\item A human-readable string to describe the machine (shown at boot time)\\
\begin{block}{}
\mint[fontsize=\small]{perl}+model = "Crystalfontz CFA-10036 Board";+
\end{block}
\item A list of {\em compatible} strings, from the most specific one
to the most general one. Mandatory to execute the right SoC specific
initializations and board specific code.\\
\begin{block}{}
\mint[fontsize=\small]{perl}+compatible = "crystalfontz,cfa10036", "fsl,imx28";+
\end{block}
\end{itemize}
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Crystalfontz CFA-10036 Device Tree, chosen/memory}
\frametitle{Crystalfontz CFA-10036, backbone}
\begin{itemize}
\item Definition of the default {\em kernel command line}. Some
additional operating-system specific entries can be added in
\code{chosen}:
\item Definition of the buses and peripherals
\begin{block}{}
\begin{minted}[fontsize=\footnotesize]{perl}
chosen {
bootargs = "console=ttyS0,115200 earlyprintk";
};
\end{minted}
\end{block}
\item Definition of the size and location of the RAM:
\begin{block}{}
\begin{minted}[fontsize=\footnotesize]{perl}
memory {
\begin{minted}[fontsize=\small]{perl}
/ {
/* Define here 'standalone' peripherals and internal buses */
memory {
device_type = "memory";
reg = <0x40000000 0x8000000>; /* 128 MB */
};
apb@80000000 {
apbh@80000000 {
/* Define apbh peripherals here */
apbx@80040000 {
/* Define apbx peripherals here */
};
};
};
};
/* Reference here existing nodes with their labels */
\end{minted}
\end{block}
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Crystalfontz CFA-10036, bus/UART}
\frametitle{Crystalfontz CFA-10036 Device Tree, enable already
described devices}
\begin{itemize}
\item Start of the internal SoC peripherals.
\item The CFA-10036 has one debug UART. It is described in the iMX28
DTSI file, so the corresponding controller should be referenced in
the board DTS and enabled:
\begin{block}{}
\begin{minted}[fontsize=\small]{perl}
apb@80000000 {
apbh@80000000 {
apbx@80040000 {
\end{minted}
\end{block}
\item The CFA-10036 has one debug UART, so the corresponding
controller is enabled:
\begin{block}{}
\begin{minted}[fontsize=\small]{perl}
duart: serial@80074000 {
\begin{minted}[fontsize=\small]{perl}
&duart {
pinctrl-names = "default";
pinctrl-0 = <&duart_pins_b>;
status = "okay";
};
\end{minted}
\end{block}
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Crystalfontz CFA-10036 Device Tree, Muxing}
\begin{itemize}
\item Definition of a few pins that will be muxed as GPIO, for LEDs and reset.
\begin{block}{}
\begin{minted}[fontsize=\tiny]{perl}
pinctrl@80018000 {
ssd1306_cfa10036: ssd1306-10036@0 {
reg = <0>;
fsl,pinmux-ids = <
0x2073 /* MX28_PAD_SSP0_D7__GPIO_2_7 */
>;
fsl,drive-strength = <0>;
fsl,voltage = <1>;
fsl,pull-up = <0>;
};

led_pins_cfa10036: leds-10036@0 {
reg = <0>;
fsl,pinmux-ids = <
0x3043 /* MX28_PAD_AUART1_RX__GPIO_3_4 */
>;
fsl,drive-strength = <0>;
fsl,voltage = <1>;
fsl,pull-up = <0>;
};
\end{minted}
\end{block}
\item It also features an USB port which is described in the SoC
DTSI but needs to be enabled:
\begin{block}{}
\begin{minted}[fontsize=\small]{perl}
&usb0 {
pinctrl-names = "default";
pinctrl-0 = <&usb0_otg_cfa10036>;
status = "okay";
};
\end{minted}
\end{block}
\end{minted}
\end{block}
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Crystalfontz CFA-10036 Device Tree, LED}
\begin{itemize}
\item One LED is connected to this platform. Note the reference to the
\code{led_pins_cfa10036} muxing configuration.
\begin{block}{}
\begin{minted}[fontsize=\small]{perl}
leds {
compatible = "gpio-leds";
pinctrl-names = "default";
pinctrl-0 = <&led_pins_cfa10036>;
\frametitle{Crystalfontz CFA-10036 Device Tree, fully describe
additional devices}
\begin{itemize}
\item The I2C bus with a Solomon SSD1306 OLED display connected on
it must be described entirely at the location where it belongs:
\begin{block}{}
\begin{minted}[fontsize=\tiny]{perl}
apbc@80040000 {
i2c0: i2c@18000 { /* This means physical offset 0x80058000 */
reg = <0x18000 0x1000>;
pinctrl-names = "default";
pinctrl-0 = <&i2c0_pins_b>;
status = "okay";
clock-frequency = <400000>;

power {
gpios = <&gpio3 4 1>;
default-state = "on";
ssd1306: oled@3c {
compatible = "solomon,ssd1306fb-i2c";
pinctrl-names = "default";
pinctrl-0 = <&ssd1306_cfa10036>;
reg = <0x3c>;
reset-gpios = <&gpio2 7 0>;
solomon,height = <32>;
solomon,width = <128>;
solomon,page-offset = <0>;
};
};
};
\end{minted}
\end{minted}
\end{block}
\item Mind the display's pin configuration that has not yet been
described
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Crystalfontz CFA-10036 Device Tree, SD Card/USB}
\frametitle{Crystalfontz CFA-10036 Device Tree, LEDs}
\begin{itemize}
\item The platform also has a USB port
\item One LED is connected to this platform, let's describe it as well
\begin{block}{}
\begin{minted}[fontsize=\small]{perl}
usb0: usb@80080000 {
pinctrl-names = "default";
pinctrl-0 = <&usb0_otg_cfa10036>;
status = "okay";
};
/ {
leds {
compatible = "gpio-leds";
pinctrl-names = "default";
pinctrl-0 = <&led_pins_cfa10036>;

power {
gpios = <&gpio3 4 1>;
default-state = "on";
};
};
\end{minted}
\end{block}
\item and an SD Card slot:
\begin{block}{}
\begin{minted}[fontsize=\small]{perl}
ssp0: ssp@80010000 {
compatible = "fsl,imx28-mmc";
pinctrl-names = "default";
pinctrl-0 = <&mmc0_4bit_pins_a
&mmc0_cd_cfg &mmc0_sck_cfg>;
bus-width = <4>;
status = "okay";
};
\end{minted}
\end{block}
\item Also mind the pin configuration that we can define at any place
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Crystalfontz CFA-10036 Device Tree, I2C bus}
\frametitle{Crystalfontz CFA-10036 Device Tree, muxing}
\begin{itemize}
\item An I2C bus, with a Solomon SSD1306 OLED display connected on
it:
\item Definition of a few pins that will be muxed as GPIO, for LEDs and reset.
\begin{block}{}
\begin{minted}[fontsize=\tiny]{perl}
i2c0: i2c@80058000 {
pinctrl-names = "default";
pinctrl-0 = <&i2c0_pins_b>;
clock-frequency = <400000>;
status = "okay";
&pinctrl {
ssd1306_cfa10036: ssd1306-10036@0 {
reg = <0>;
fsl,pinmux-ids = <0x2073>; /* MX28_PAD_SSP0_D7__GPIO_2_7 */
fsl,drive-strength = <0>;
fsl,voltage = <1>;
fsl,pull-up = <0>;
};

ssd1306: oled@3c {
compatible = "solomon,ssd1306fb-i2c";
pinctrl-names = "default";
pinctrl-0 = <&ssd1306_cfa10036>;
reg = <0x3c>;
reset-gpios = <&gpio2 7 0>;
solomon,height = <32>;
solomon,width = <128>;
solomon,page-offset = <0>;
led_pins_cfa10036: leds-10036@0 {
reg = <0>;
fsl,pinmux-ids = <0x3043>; /* MX28_PAD_AUART1_RX__GPIO_3_4 */
fsl,drive-strength = <0>;
fsl,voltage = <1>;
fsl,pull-up = <0>;
};
};
\end{minted}
Expand Down Expand Up @@ -343,7 +325,8 @@
\kfile{arch/arm/boot/dts/Makefile}:
\begin{block}{}
\begin{minted}{make}
dtb-$(CONFIG_ARCH_MXS) += imx28-cfa10036.dtb \
dtb-$(CONFIG_ARCH_MXS) +=
imx28-cfa10036.dtb \
imx28-cfa10037.dtb \
imx28-cfa10049.dtb \
imx28-cfa10055.dtb \
Expand Down

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