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[ Upstream commit6cbe45d8ac] Oxford Semiconductor PCIe (Tornado) serial port devices are driven by a fixed 62.5MHz clock input derived from the 100MHz PCI Express clock. In the enhanced (650) mode, which we select in `autoconfig_has_efr' by setting the ECB bit in the EFR register, and in the absence of clock reconfiguration, which we currently don't do, the clock rate is divided only by the oversampling rate of 16 as it is supplied to the baud rate generator, yielding the baud base of 3906250. This comes from the reset values of the TCR and MCR[7] registers which are both zero[1][2][3][4], choosing the oversampling rate of 16 and the normal (divide by 1) baud rate generator prescaler respectively. This is the rate that is divided by the value held in the divisor latch to determine the baud rate used. Replace the incorrect baud base of 4000000 with the right value of 3906250 then. References: [1] "OXPCIe200 PCI Express Multi-Port Bridge", Oxford Semiconductor, Inc., DS-0045, 10 Nov 2008, Section "Reset Configuration", p. 72 [2] "OXPCIe952 PCI Express Bridge to Dual Serial & Parallel Port", Oxford Semiconductor, Inc., DS-0046, Mar 06 08, Section "Reset Configuration", p. 27 [3] "OXPCIe954 PCI Express Bridge to Quad Serial Port", Oxford Semiconductor, Inc., DS-0047, Feb 08, Section "Reset Configuration", p. 28 [4] "OXPCIe958 PCI Express Bridge to Octal Serial Port", Oxford Semiconductor, Inc., DS-0048, Feb 08, Section "Reset Configuration", p. 28 Fixes:7106b4e333("8250: Oxford Semiconductor Devices") Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Link: https://lore.kernel.org/r/alpine.DEB.2.21.2106100203510.5469@angie.orcam.me.uk Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@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.