[bootlin/training-materials updates] master: common: printk: add debug logs troubleshooting (cf7c4d2b)

[Alexis Lothoré]

Repository : https://github.com/bootlin/training-materials
On branch  : master
Link       : https://github.com/bootlin/training-materials/commit/cf7c4d2b1594f90b2e39f1641500478e80cf9821

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

commit cf7c4d2b1594f90b2e39f1641500478e80cf9821
Author: Alexis Lothoré <alexis.lothore at bootlin.com>
Date:   Fri Jul 7 10:39:20 2023 +0200

    common: printk: add debug logs troubleshooting
    
    Developpers may struggle to see logs inserted in their kernel or drivers.
    Since there are multiple possibles reasons, provide a short troubleshooting
    list to check to make sure that pr_debug/dev_dbg calls are properly
    generated
    Enable this new slide for debugging only for now
    
    Fixes #204
    
    Signed-off-by: Alexis Lothoré <alexis.lothore at bootlin.com>


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cf7c4d2b1594f90b2e39f1641500478e80cf9821
 common/printk.tex | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/common/printk.tex b/common/printk.tex
index 5c267f0f..44d0b88a 100644
--- a/common/printk.tex
+++ b/common/printk.tex
@@ -155,3 +155,31 @@ dev_info(&pdev->dev, "in probe\n");
   \end{itemize}
 \end{frame}
 }{}
+
+\ifthenelse{\equal{\training}{debugging}}{
+\begin{frame}
+  \frametitle{Debug logs troubleshooting}
+  \begin{itemize}
+    \item Make sure that your debug call is enabled: it must be visible in
+    \code{control} file in debugfs \textbf{and} be actived (\code{=p})
+    \item Is your log output only in kernel log buffer ?
+    \begin{itemize}
+      \item You can see it thanks to \code{dmesg}
+      \item You can lower \code{loglevel} to output it to console directly
+      \item You can also set \code{ignore_loglevel} in kernel command line to
+      force all kernel logs to console
+    \end{itemize}
+    \item If you are working on an out-of-tree module, you may prefer to define \code{DEBUG} in
+    your module source or Makefile instead of using dynamic debug
+    \item If configuration is done through kernel commandline, is it
+    properly interpreted ?
+    \begin{itemize}
+      \item Starting from 5.14, kernel will let you know about faulty
+      commandline:\\
+      \code{Unknown kernel command line parameters foo, will be passed to user
+      space.}
+      \item You may need to take care of special characters escaping (e.g: quotes)
+    \end{itemize}
+  \end{itemize}
+\end{frame}
+}{}
\ No newline at end of file