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Petr Machata says: ==================== mlxsw: Move allocation of LAG table to the driver PGT is an in-HW table that maps addresses to sets of ports. Then when some HW process needs a set of ports as an argument, instead of embedding the actual set in the dynamic configuration, what gets configured is the address referencing the set. The HW then works with the appropriate PGT entry. Within the PGT is placed a LAG table. That is a contiguous block of PGT memory where each entry describes which ports are members of the corresponding LAG port. The PGT is split to two parts: one managed by the FW, and one managed by the driver. Historically, the FW part included also the LAG table, referred to as FW LAG mode. Giving the responsibility for placement of the LAG table to the driver, referred to as SW LAG mode, makes the whole system more flexible. The FW currently supports both FW and SW LAG modes. To shed complexity, the FW should in the future only support SW LAG mode. Hence this patchset, where support for placement of LAG is added to mlxsw. There are FW versions out there that do not support SW LAG mode, and on Spectrum-1 in particular, there is no plan to support it at all. mlxsw will therefore have to support both modes of operation. Another aspect is that at least on Spectrum-1, there are FW versions out there that claim to support driver-placed LAG table, but then reject or ignore configurations enabling the same. The driver thus has to have a say in whether an attempt to configure SW LAG mode should even be done. The feature is therefore expressed in terms of "does the driver prefer SW LAG mode?", and "what LAG mode the PCI module managed to configure the FW with". This is unlike current flood mode configuration, where the driver can give a strict value, and that's what gets configured. But it gives a chance to the driver to determine whether LAG mode should be enabled at all. The "does the driver prefer SW LAG mode?" bit is expressed as a boolean lag_mode_prefer_sw. The reason for this is largely another feature that will be introduced in a follow-up patchset: support for CFF flood mode. The driver currently requires that the FW be configured with what is called controlled flood mode. But on capable systems, CFF would be preferred. So there are two values in flight: the preferred flood mode, and the fallback. This could be expressed with an array of flood modes ordered by preference, but that looks like an overkill in comparison. This flag/value model is then reused for LAG mode as well, except the fallback value is absent and implied to be FW, because there are no other values to choose from. The patchset progresses as follows: - Patches #1 to #5 adjust reg.h and cmd.h with new register fields, constants and remarks. - Patches #6 and #7 add the ability to request SW LAG mode and to query the LAG mode that was actually negotiated. This is where the abovementioned lag_mode_prefer_sw flag is added. - Patches #7 to #9 generalize PGT allocations to make it possible to allocate the LAG table, which is done in patch #10. - In patch #11, toggle lag_mode_prefer_sw on Spectrum-2 and above, which makes the newly-added code live. ==================== Signed-off-by: David S. Miller <davem@davemloft.net> |
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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.