doc: Make SD card peripheral docs more generic, fix one acronym

Fixes an issue in which "SDHC" had been incorrectly expanded to
"Secure Digital High Capacity" instead of "SD Host Controller".

Since this page is listed under "Peripherals" and since the
SD Host Controller API is not supposed to be used by applications,
the more generic and recognizable title "SD card interface" is used,
and users are pointed to pages relevant to them (disk access API
and SD card subsystem).

Signed-off-by: Egill Sigurdur <[email protected]>

Author: egilll

doc/hardware/peripherals/sdhc.rst

@@ -1,30 +1,31 @@
 .. _sdhc_api:
 
-
-Secure Digital High Capacity (SDHC)
+Secure Digital (SD card) interface
 ###################################
 
-The SDHC api offers a generic interface for interacting with an SD host
-controller device. It is used by the SD subsystem, and is not intended to be
-directly used by the application
+Zephyr can communicate with an attached SD card either using a system's native
+SD card interface or over SPI (Serial Peripheral Interface). Some devices can
+also communicate with MMC (MultiMediaCard) devices.
+
+Applications can use Zephyr's :ref:`the disk access API <disk_access_api>`
+to use SD cards as storage devices, or Zephyr's SD card subsystem to
+directly read from and write to a card.
 
-Basic Operation
-***************
+SD Host Controller (SDHC)
+*************************
 
-SD Host Controller
-==================
+An SD host controller (SDHC) is a device capable of sending commands to an
+SD card. These commands can be sent using a system's native SD card interface,
+or over SPI.
 
-An SD host controller is a device capable of sending SD commands to an attached
-SD card. These commands can be sent using the native SD protocol, or over SPI.
-Some SD host controllers are also capable of communicating with MMC devices.
-The SDHC api is designed to provide a generic way to send commands to and
-interact with attached SD devices.
+Applications should generally not use the SD host controller API directly,
+instead they should use Zephyr's SD card subsystem.
 
 Requests
 ========
 
-The core of the SDHC api is the :c:func:`sdhc_request` api. Requests contain a
-:c:struct:`sdhc_command` command structure, and an optional
+The core of the SD host controller (SDHC) API is the :c:func:`sdhc_request` API.
+Requests contain a :c:struct:`sdhc_command` command structure, and an optional
 :c:struct:`sdhc_data` data structure. The caller may check the return code,
 or the ``response`` field of the SD command structure to determine if the
 SDHC request succeeded. The data structure allows the caller to specify a
@@ -35,7 +36,7 @@ command opcode provided.
 Host Controller I/O
 ===================
 
-The :c:func:`sdhc_set_io` api allows the user to change I/O settings of the SD
+The :c:func:`sdhc_set_io` API allows the user to change I/O settings of the SD
 host controller, such as clock frequency, I/O voltage, and card power. Not all
 controllers will support applying all I/O settings. For example, SPI mode
 controllers typically cannot toggle power to the SD card.