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commit3751c3d34cupstream. The recent addition of timestamp correction to compensate the CDC error introduced a subtle signed/unsigned bug in stmmac_get_tx_hwtstamp() while it managed for some obscure reason to avoid that in stmmac_get_rx_hwtstamp(). The issue is: s64 adjust = 0; u64 ns; adjust += -(2 * (NSEC_PER_SEC / priv->plat->clk_ptp_rate)); ns += adjust; works by chance on 64bit, but falls apart on 32bit because the compiler knows that adjust fits into 32bit and then treats the addition as a u64 + u32 resulting in an off by ~2 seconds failure. The RX variant uses an u64 for adjust and does the adjustment via ns -= adjust; because consistency is obviously overrated. Get rid of the pointless zero initialized adjust variable and do: ns -= (2 * NSEC_PER_SEC) / priv->plat->clk_ptp_rate; which is obviously correct and spares the adjust obfuscation. Aside of that it yields a more accurate result because the multiplication takes place before the integer divide truncation and not afterwards. Stick the calculation into an inline so it can't be accidentally disimproved. Return an u32 from that inline as the result is guaranteed to fit which lets the compiler optimize the substraction. Cc: stable@vger.kernel.org Fixes:3600be5f58("net: stmmac: add timestamp correction to rid CDC sync error") Reported-by: Benedikt Spranger <b.spranger@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Benedikt Spranger <b.spranger@linutronix.de> Tested-by: Kurt Kanzenbach <kurt@linutronix.de> # Intel EHL Link: https://lore.kernel.org/r/87mtm578cs.ffs@tglx Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.