[bootlin/training-materials updates] master: kernel-driver-development-debugging: Add dedicated slies about early printl WIP (6515dccd)

[Gregory CLEMENT]

Repository : https://github.com/bootlin/training-materials
On branch  : master
Link       : https://github.com/bootlin/training-materials/commit/6515dccd9c160be9ee061cb4cbc8e080d1b98b98

>---------------------------------------------------------------

commit 6515dccd9c160be9ee061cb4cbc8e080d1b98b98
Author: Gregory CLEMENT <gregory.clement at bootlin.com>
Date:   Mon Mar 15 10:01:47 2021 +0100

    kernel-driver-development-debugging: Add dedicated slies about early printl WIP
    
    Signed-off-by: Gregory CLEMENT <gregory.clement at bootlin.com>


>---------------------------------------------------------------

6515dccd9c160be9ee061cb4cbc8e080d1b98b98
 .../kernel-driver-development-debugging.tex          | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/slides/kernel-driver-development-debugging/kernel-driver-development-debugging.tex b/slides/kernel-driver-development-debugging/kernel-driver-development-debugging.tex
index dc925b42..0250fc1d 100644
--- a/slides/kernel-driver-development-debugging/kernel-driver-development-debugging.tex
+++ b/slides/kernel-driver-development-debugging/kernel-driver-development-debugging.tex
@@ -100,6 +100,22 @@ dev_info(&pdev->dev, "in probe\n");
   \end{itemize}
 \end{frame}
 
+\begin{frame}
+  \frametitle{Printing message early during the boot}
+  \begin{itemize}
+  \item Messages are visible only once the console driver has been initialized.
+  \item The console driver is simpler than a complete serial driver
+    and is initialize earlier than serial driver
+  \item But core subsystem are still initialized before, such as
+    memory, timer or interrupt, if a crash occurred there, then no
+    message are visible
+  \item on arm (32 bits) architecture most of the SoC implement the
+    \code{early_printk} support
+  \item \Activate it with kconfig{CONFIG_DEBUG_LL} and \kconfig{CONFIG_EARLYPRINTK} and add
+    \code{earlyprintk} to the kernel command line.
+  \end{itemize}
+\end{frame}
+
 \begin{frame}
   \frametitle{DebugFS}
   A virtual filesystem to export debugging information to user space.
@@ -276,9 +292,5 @@ dev_info(&pdev->dev, "in probe\n");
     \item Is turned on by default
     \item To get oops messages with symbol names instead of raw addresses
     \end{itemize}
-  \item On ARM, if your kernel doesn't boot or hangs without any
-    message, you can activate early debugging options
-    (\kconfig{CONFIG_DEBUG_LL} and \kconfig{CONFIG_EARLYPRINTK}), and add
-    \code{earlyprintk} to the kernel command line.
   \end{itemize}
 \end{frame}