docs: rework the driver-api top-level page

Add subsections in an attempt to bring a bit order to this page; also sort
most subsections into alphabetical order.  With luck all this will help to
prevent merge conflicts on this page due to everybody adding entries at the
end.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/87plxtm2oo.fsf@meer.lwn.net

Documentation/driver-api/index.rst

@@ -9,110 +9,141 @@ of device drivers.  This document is an only somewhat organized collection
 of some of those interfaces — it will hopefully get better over time!  The
 available subsections can be seen below.
 
-.. toctree::
-   :caption: Table of contents
-   :maxdepth: 2
 
-   driver-model/index
+General information for driver authors
+======================================
+
+This section contains documentation that should, at some point or other, be
+of interest to most developers working on device drivers.
+
+.. toctree::
+   :maxdepth: 1
+
    basics
+   driver-model/index
+   device_link
    infrastructure
    ioctl
-   early-userspace/index
    pm/index
-   clk
+
-   device-io
+Useful support libraries
-   dma-buf
+========================
-   device_link
+
-   component
+This section contains documentation that should, at some point or other, be
-   message-based
+of interest to most developers working on device drivers.
-   infiniband
+
-   aperture
+.. toctree::
-   frame-buffer
+   :maxdepth: 1
-   regulator
+
-   reset
+   early-userspace/index
-   iio/index
-   input
-   usb/index
-   firewire
-   pci/index
-   cxl/index
-   spi
-   i2c
-   ipmb
-   ipmi
-   i3c/index
-   interconnect
-   devfreq
-   hsi
-   edac
-   scsi
-   libata
-   target
-   mailbox
-   mtdnand
-   miscellaneous
-   mei/index
-   mtd/index
-   mmc/index
-   nvdimm/index
-   w1
-   rapidio/index
-   s390-drivers
-   vme
-   80211/index
-   uio-howto
-   firmware/index
-   pin-control
-   gpio/index
-   md/index
-   media/index
-   misc_devices
-   nfc/index
-   dmaengine/index
-   slimbus
-   soundwire/index
-   thermal/index
-   fpga/index
-   acpi/index
-   auxiliary_bus
-   backlight/lp855x-driver.rst
    connector
-   console
+   device-io
-   eisa
+   devfreq
-   isa
+   dma-buf
+   component
    io-mapping
    io_ordering
-   generic-counter
+   uio-howto
-   memory-devices/index
-   men-chameleon-bus
-   ntb
-   nvmem
-   parport-lowlevel
-   pps
-   ptp
-   phy/index
-   pwm
-   pldmfw/index
-   rfkill
-   serial/index
-   sm501
-   surface_aggregator/index
-   switchtec
-   sync_file
-   tty/index
    vfio-mediated-device
    vfio
    vfio-pci-device-specific-driver-acceptance
+
+Bus-level documentation
+=======================
+
+.. toctree::
+   :maxdepth: 1
+
+   auxiliary_bus
+   cxl/index
+   eisa
+   firewire
+   i3c/index
+   isa
+   men-chameleon-bus
+   pci/index
+   rapidio/index
+   slimbus
+   usb/index
    virtio/index
-   xilinx/index
+   vme
+   w1
    xillybus
-   zorro
+
-   hte/index
+
-   wmi
+Subsystem-specific APIs
-   dpll
+=======================
-   wbrf
+
+.. toctree::
+   :maxdepth: 1
+
+   80211/index
+   acpi/index
+   backlight/lp855x-driver.rst
+   clk
+   console
    crypto/index
+   dmaengine/index
+   dpll
+   edac
+   firmware/index
+   fpga/index
+   frame-buffer
+   aperture
+   generic-counter
+   gpio/index
+   hsi
+   hte/index
+   i2c
+   iio/index
+   infiniband
+   input
+   interconnect
+   ipmb
+   ipmi
+   libata
+   mailbox
+   md/index
+   media/index
+   mei/index
+   memory-devices/index
+   message-based
+   misc_devices
+   miscellaneous
+   mmc/index
+   mtd/index
+   mtdnand
+   nfc/index
+   ntb
+   nvdimm/index
+   nvmem
+   parport-lowlevel
+   phy/index
+   pin-control
+   pldmfw/index
+   pps
+   ptp
+   pwm
+   regulator
+   reset
+   rfkill
+   s390-drivers
+   scsi
+   serial/index
+   sm501
+   soundwire/index
+   spi
+   surface_aggregator/index
+   switchtec
+   sync_file
+   target
    tee
+   thermal/index
+   tty/index
+   wbrf
+   wmi
+   xilinx/index
+   zorro
 
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