fix: How_To_Guides: Add Guide for Changing Size of CMA Region

Many components use the CMA to read and write memory. This how-to was
originally placed only in the Wave5 documenation. Lets separate this to
a how-to guide so that it can be more generic acorss domains.

Signed-off-by: Brandon Brnich <[email protected]>

Author: b-brnich

source/linux/How_to_Guides/Target/How_To_Carve_Out_CMA.rst

@@ -0,0 +1,45 @@
+
+How to Configure the CMA Size
+=============================
+
+Contiguous Memory allocation (CMA) is commonly used by memory-to-memory (M2M) devices that do not have
+have MMU support. By default in Linux, the CMA size will be 32 MB. For the common TI board, this is far
+too small. There are a handful of components that need to use CMA in order for proper operation as well as
+achieving optimal performance. These components include, but are not limited to, the multimedia Codecs, CSI,
+and TIDSS. TI has already increased the amount of CMA that comes in |__SDK_FULL_NAME__|. The amount that has
+been allocated can be checked by running the following command on target:
+
+.. code-block:: console
+
+   target$ cat /proc/meminfo | grep Cma
+
+After executing, an output similar to the one below will be seen.
+
+.. code-block:: console
+
+   CmaTotal:         589824 kB
+   CmaFree:          583984 kB
+
+These logs can be used to obtain the amount of CMA that has been allocated and how much of that is still available
+for use. Depending on the particular use case, it may be of interest to decrease the size of this allocation pool.
+To do so, locate the device tree (.dts) file that contains the main domain for the target board. For example, if
+using the AM62PX SoC, open up :file:`arch/arm64/boot/dts/ti/k3-am62p5-sk.dts`. These device tree files contain a
+node for reserved memory. A portion of this reserved memory area is for CMA, therefore the area has been named
+`linux,cma`. This node contains an attribute called size; changing the value of this attribute cause the CMA region
+to grow or shrink. Once attribute is changed to desired value, save and close the dts file so it can be compiled into
+proper device tree blob (.dtb). Update the target with new .dtb file and check that new CMA region matches the size
+set in the device tree.
+
+CMA allocation can also be changed without re-compilation of device tree. One can stop at u-boot prompt during boot
+and update the CMA parameter as shown below:
+
+.. code-block:: console
+
+   target # setenv args_all $args_all cma=1000M
+   target # boot
+
+.. note::
+
+   Allocating at u-boot tends to place the CMA in the lower 32 bit region of memory. Many of the common components have been
+   ported to operate in the higher 48 bit region of memory. It is recommended to take the approach with changing device tree,
+   but this method is fine for quick validation.

source/linux/How_to_Guides_Developer_Notes.rst

@@ -50,3 +50,4 @@ Developer Notes
    How_to_Guides/Host/Program_MMC_boot_media
    How_to_Guides/FAQ/Tda4_Latest_FAQs
    How_to_Guides/FAQ/How_to_run_BIST_on_a_core
+   How_to_Guides/Target/How_To_Carve_Out_CMA