[PATCH net] docs: net: clarify the NAPI rules around XDP Tx

[Jakub Kicinski <kuba@kernel.org>]

page pool and XDP should not be accessed from IRQ context
which may happen if drivers try to clean up XDP TX with
NAPI budget of 0.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: corbet@lwn.net
CC: linux-doc@vger.kernel.org
---
 Documentation/networking/napi.rst | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/Documentation/networking/napi.rst b/Documentation/networking/napi.rst
index a7a047742e93..7bf7b95c4f7a 100644
--- a/Documentation/networking/napi.rst
+++ b/Documentation/networking/napi.rst
@@ -65,15 +65,16 @@ argument - drivers can process completions for any number of Tx
 packets but should only process up to ``budget`` number of
 Rx packets. Rx processing is usually much more expensive.
 
-In other words, it is recommended to ignore the budget argument when
-performing TX buffer reclamation to ensure that the reclamation is not
-arbitrarily bounded; however, it is required to honor the budget argument
-for RX processing.
+In other words for Rx processing the ``budget`` argument limits how many
+packets driver can process in a single poll. Rx specific APIs like page
+pool or XDP cannot be used at all when ``budget`` is 0.
+skb Tx processing should happen regardless of the ``budget``, but if
+the argument is 0 driver cannot call any XDP (or page pool) APIs.
 
 .. warning::
 
-   The ``budget`` argument may be 0 if core tries to only process Tx completions
-   and no Rx packets.
+   The ``budget`` argument may be 0 if core tries to only process
+   skb Tx completions and no Rx or XDP packets.
 
 The poll method returns the amount of work done. If the driver still
 has outstanding work to do (e.g. ``budget`` was exhausted)
-- 
2.41.0