[bootlin/training-materials updates] master: Kernel slides: improve devm_ memory allocation example (6ab1b6d7)

[Michael Opdenacker]

Repository : https://github.com/bootlin/training-materials
On branch  : master
Link       : https://github.com/bootlin/training-materials/commit/6ab1b6d7a788beddeec47b42a87f370e1ae949cd

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

commit 6ab1b6d7a788beddeec47b42a87f370e1ae949cd
Author: Michael Opdenacker <michael.opdenacker at bootlin.com>
Date:   Wed Oct 28 17:05:28 2020 +0100

    Kernel slides: improve devm_ memory allocation example
    
    Signed-off-by: Michael Opdenacker <michael.opdenacker at bootlin.com>


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

6ab1b6d7a788beddeec47b42a87f370e1ae949cd
 slides/kernel-frameworks2/kernel-frameworks2.tex | 34 +++++++++++++-----------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/slides/kernel-frameworks2/kernel-frameworks2.tex b/slides/kernel-frameworks2/kernel-frameworks2.tex
index d3bb567f..c684583f 100644
--- a/slides/kernel-frameworks2/kernel-frameworks2.tex
+++ b/slides/kernel-frameworks2/kernel-frameworks2.tex
@@ -198,7 +198,8 @@ Many more operations exist. All of them are optional.
     \item Allows to extend the driver capabilities beyond the limited
       read/write API.
     \item For example: changing the speed of a serial port, setting
-      video output format, querying a device serial number...
+      video output format, querying a device serial number... Used
+      extensively in the V4L2 (video) and Alsa (sound) driver frameworks.
     \item \code{cmd} is a number identifying the operation to perform
     \item \code{arg} is the optional argument passed as third argument
       of the \code{ioctl()} system call. Can be an integer, an
@@ -411,26 +412,25 @@ static int xxxfb_probe (struct pci_dev *dev,
     \begin{minted}{c}
 int foo_probe(struct platform_device *pdev)
 {
-        foo_t *foo;
-
-        foo = kmalloc(sizeof(struct foo_t),
-                      GFP_KERNEL);
+        foo_t *foo = kmalloc(sizeof(struct foo_t),
+                                    GFP_KERNEL);
+        /* Register to framework, store
+         * reference to framework structure in foo */
         ...
         if (failure) {
                 kfree(foo);
                 return -EBUSY;
         }
-        ...
         platform_set_drvdata(pdev, foo);
-        pm_runtime_enable(&pdev->dev);
-        pm_runtime_get_sync(&pdev->dev);
         return 0;
 }
 
 void foo_remove(struct platform_device *pdev)
 {
-        pm_runtime_disable(&pdev->dev);
         foo_t *foo = platform_get_drvdata(pdev);
+        /* Retrieve framework structure from foo
+           and unregister it */
+        ...
         kfree(foo);
 }
     \end{minted}
@@ -441,23 +441,25 @@ void foo_remove(struct platform_device *pdev)
     \begin{minted}{c}
 int foo_probe(struct platform_device *pdev)
 {
-        foo_t *foo;
-
-        foo = devm_kmalloc(&pdev->dev,
+        foo_t *foo = devm_kmalloc(&pdev->dev,
                            sizeof(struct foo_t),
                            GFP_KERNEL);
+        /* Register to framework, store
+         * reference to framework structure in foo */
         ...
         if (failure)
                 return -EBUSY;
-        ...
-        pm_runtime_enable(&pdev->dev);
-        pm_runtime_get_sync(&pdev->dev);
+        platform_set_drvdata(pdev, foo);
         return 0;
 }
 
 void foo_remove(struct platform_device *pdev)
 {
-        pm_runtime_disable(&pdev->dev);
+        foo_t *foo = platform_get_drvdata(pdev);
+        /* Retrieve framework structure from foo
+           and unregister it */
+        ...
+        /* foo automatically freed */
 }
     \end{minted}
   \end{block}