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7cf0324ba0
When SPI transfer is being prepared, the spi-s3c64xx driver will call
clk_set_rate() to change the rate of SPI source clock (IPCLK). But IPCLK
is a gate (leaf) clock, so it must propagate the rate change up the
clock tree, so that corresponding MUX/DIV clocks can actually change
their values. Add CLK_SET_RATE_PARENT flag to corresponding clocks for
all USI instances in GS101 PERIC1: USI{0, 9, 10, 11, 12, 13}. This change
involves the following clocks:
PERIC1 USI*:
Clock Div range MUX Selection
-------------------------------------------------------------------
gout_peric1_peric1_top0_ipclk_* - -
dout_peric1_usi*_usi /1..16 -
mout_peric1_usi*_usi_user - {24.5 MHz, 400 MHz}
With input clock of 400 MHz this scheme provides the following IPCLK
rate range, for each USI block:
PERIC1 USI*: 1.5 MHz ... 400 MHz
Accounting for internal /4 divider in SPI blocks, and because the max
SPI frequency is limited at 50 MHz, it gives us next SPI SCK rates:
PERIC1 USI_SPI*: 384 KHz ... 49.9 MHz
Which shall be fine for the applications of the SPI bus.
Note that with this we allow the reparenting of the MUX_USIx clocks to
OSCCLK. Each instance of the USI IP has its own MUX_USI clock, thus the
reparenting of a MUX_USI clock corresponds to a single instance of the
USI IP. The datasheet mentions OSCCLK just in the low-power mode
context, but the downstream driver reparents too the MUX_USI clocks to
OSCCLK. Follow the downstream driver and do the same.
Fixes:
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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 reStructuredText 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.