doc: split VFIO section in Linux guide

The VFIO section of the page about Linux drivers was rather long and
unstructured. This can be improved by splitting it up into subsections,
to cover the specifics of memory limits and creating VFs. When moving
the various text notes into the relevant subsections, we can drop the
note about kernels earlier than 3.6, since DPDK no longer supports
kernels that old.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

diff --git a/doc/guides/linux_gsg/linux_drivers.rst b/doc/guides/linux_gsg/linux_drivers.rst
index bd649db929fd03d1303fcd085a4c2b56d9ee2fa6..f9c24e9456b5db358d034aeea4078e21dd1c41a5 100644 (file)
--- a/doc/guides/linux_gsg/linux_drivers.rst
+++ b/doc/guides/linux_gsg/linux_drivers.rst
@@ -122,6 +122,22 @@ To make use of VFIO, the ``vfio-pci`` module must be loaded:
 VFIO kernel is usually present by default in all distributions,
 however please consult your distributions documentation to make sure that is the case.
 
+To make use of full VFIO functionality,
+both kernel and BIOS must support and be configured
+to use IO virtualization (such as Intel\ |reg| VT-d).
+
+.. note::
+
+   In most cases, specifying "iommu=on" as kernel parameter should be enough to
+   configure the Linux kernel to use IOMMU.
+
+For proper operation of VFIO when running DPDK applications as a non-privileged user, correct permissions should also be set up.
+For more information, please refer to :ref:`Running_Without_Root_Privileges`.
+
+
+VFIO Memory Mapping Limits
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 For DMA mapping of either external memory or hugepages, VFIO interface is used.
 VFIO does not support partial unmap of once mapped memory. Hence DPDK's memory is
 mapped in hugepage granularity or system page granularity. Number of DMA
@@ -132,6 +148,9 @@ VFIO module parameter ``dma_entry_limit`` with a default value of 64K.
 When application is out of DMA entries, these limits need to be adjusted to
 increase the allowed limit.
 
+Creating Virtual Functions using vfio-pci
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 Since Linux version 5.7,
 the ``vfio-pci`` module supports the creation of virtual functions.
 After the PF is bound to ``vfio-pci`` module,
@@ -194,27 +213,11 @@ The token will be used for all PF and VF ports within the application.
       <build_dir>/app/dpdk-testpmd -l 26-29 -n 4 -a 86:02.0 \
       --vfio-vf-token=14d63f20-8445-11ea-8900-1f9ce7d5650d --file-prefix=vf0 -- -i
 
-To make use of full VFIO functionality,
-both kernel and BIOS must support and be configured
-to use IO virtualization (such as Intel\ |reg| VT-d).
-
-.. note::
-
-   Linux versions earlier than version 3.6 do not support VFIO.
-
 .. note::
 
    Linux versions earlier than version 5.7 do not support the creation of
    virtual functions within the VFIO framework.
 
-.. note::
-
-   In most cases, specifying "iommu=on" as kernel parameter should be enough to
-   configure the Linux kernel to use IOMMU.
-
-For proper operation of VFIO when running DPDK applications as a non-privileged user, correct permissions should also be set up.
-For more information, please refer to :ref:`Running_Without_Root_Privileges`.
-
 .. _vfio_noiommu:
 
 VFIO no-IOMMU mode