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Some chip versions have a hw bug resulting in lost door bell rings. To work around this the doorbell is also rung whenever we still have tx descriptors in flight after having cleaned up tx descriptors. These PCI(e) writes come at a cost, therefore let's reduce the number of extra doorbell rings. If skb is NULL then this means: - last cleaned-up descriptor belongs to a skb with at least one fragment and last fragment isn't marked as sent yet - hw is in progress sending the skb, therefore no extra doorbell ring is needed for this skb - once last fragment is marked as transmitted hw will trigger a tx done interrupt and we come here again (with skb != NULL) and ring the doorbell if needed Therefore skip the workaround doorbell ring if skb is NULL. Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com> Link: https://lore.kernel.org/r/0a15a83c-aecf-ab51-8071-b29d9dcd529a@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.