[PATCH v3] doc: add known igb_uio issue for i40e

[Qiming Yang <qiming.yang@intel.com>]

When insmod "igb_uio" with "intr_mode=legacy and test link
status interrupt. Since INTx interrupt is not supported by
X710/XL710/XXV710, it will cause Input/Output error when
reading file descriptor.

Signed-off-by: Qiming Yang <qiming.yang@intel.com>
Acked-by Jingjing Wu <jingjing.wu@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
---
v2 changes:
* move the description to rel_notes/known_issues.rst
v3 changes:
* fixed a doc build warning
---
---
 doc/guides/rel_notes/known_issues.rst | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/doc/guides/rel_notes/known_issues.rst b/doc/guides/rel_notes/known_issues.rst
index f149ac7..a5592b0 100644
--- a/doc/guides/rel_notes/known_issues.rst
+++ b/doc/guides/rel_notes/known_issues.rst
@@ -697,3 +697,27 @@ virtio tx_burst() function cannot do TSO on shared packets
 
 **Driver/Module**:
    Poll Mode Driver (PMD).
+
+
+igb uio legacy mode can not be used in X710/XL710/XXV710
+--------------------------------------------------------
+
+**Description**:
+   X710/XL710/XXV710 NICs lack support for indicating INTx is asserted via the interrupt
+   bit in the PCI status register. Linux delected them from INTx support table. The related
+   link `<https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/drivers/pci/quirks.c?id=8bcf4525c5d43306c5fd07e132bc8650e3491aec>`_.
+
+**Implication**:
+   When insmod ``igb_uio`` with ``intr_mode=legacy`` and test link status interrupt. Since
+   INTx interrupt is not supported by X710/XL710/XXV710, it will cause Input/Output error
+   when reading file descriptor.
+
+**Resolution/Workaround**:
+   Do not bind ``igb_uio`` with legacy mode in X710/XL710/XXV710 NICs, or do not use kernel
+   version >4.7 when you bind ``igb_uio`` with legacy mode.
+
+**Affected Environment/Platform**:
+   ALL.
+
+**Driver/Module**:
+   Poll Mode Driver (PMD).
-- 
2.4.11