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In the blamed commit, it was not noticed that one implementation of
chip->info->ops->phylink_get_caps(), called by mv88e6xxx_get_caps(),
may access hardware registers, and in doing so, it takes the
mv88e6xxx_reg_lock(). Namely, this is mv88e6352_phylink_get_caps().
This is a problem because mv88e6xxx_get_caps(), apart from being
a top-level function (method invoked by dsa_switch_ops), is now also
directly called from mv88e6xxx_setup_port(), which runs under the
mv88e6xxx_reg_lock() taken by mv88e6xxx_setup(). Therefore, when running
on mv88e6352, the reg_lock would be acquired a second time and the
system would deadlock on driver probe.
The things that mv88e6xxx_setup() can compete with in terms of register
access with are the IRQ handlers and MDIO bus operations registered by
mv88e6xxx_probe(). So there is a real need to acquire the register lock.
The register lock can, in principle, be dropped and re-acquired pretty
much at will within the driver, as long as no operations that involve
waiting for indirect access to complete (essentially, callers of
mv88e6xxx_smi_direct_wait() and mv88e6xxx_wait_mask()) are interrupted
with the lock released. However, I would guess that in mv88e6xxx_setup(),
the critical section is kept open for such a long time just in order to
optimize away multiple lock/unlock operations on the registers.
We could, in principle, drop the reg_lock right before the
mv88e6xxx_setup_port() -> mv88e6xxx_get_caps() call, and
re-acquire it immediately afterwards. But this would look ugly, because
mv88e6xxx_setup_port() would release a lock which it didn't acquire, but
the caller did.
A cleaner solution to this issue comes from the observation that struct
mv88e6xxxx_ops methods generally assume they are called with the
reg_lock already acquired. Whereas mv88e6352_phylink_get_caps() is more
the exception rather than the norm, in that it acquires the lock itself.
Let's enforce the same locking pattern/convention for
chip->info->ops->phylink_get_caps() as well, and make
mv88e6xxx_get_caps(), the top-level function, acquire the register lock
explicitly, for this one implementation that will access registers for
port 4 to work properly.
This means that mv88e6xxx_setup_port() will no longer call the top-level
function, but the low-level mv88e6xxx_ops method which expects the
correct calling context (register lock held).
Compared to chip->info->ops->phylink_get_caps(), mv88e6xxx_get_caps()
also fixes up the supported_interfaces bitmap for internal ports, since
that can be done generically and does not require per-switch knowledge.
That's code which will no longer execute, however mv88e6xxx_setup_port()
doesn't need that. It just needs to look at the mac_capabilities bitmap.
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.