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The DHCOM SoM has two options for supplying ETHRX clock to the DWMAC block and PHY. Either (1) ETHCK_K generates 50 MHz clock on ETH_CLK pad for the PHY and the same 50 MHz clock are fed back to ETHRX via internal eth_clk_fb clock connection OR (2) ETH_CLK is not used at all, MCO2 generates 50 MHz clock on MCO2 output pad for the PHY and the same MCO2 clock are fed back into ETHRX via ETH_RX_CLK input pad using external pad-to-pad connection. Option (1) has two downsides. ETHCK_K is supplied directly from either PLL3_Q or PLL4_P, hence the PLL output is limited to exactly 50 MHz and since the same PLL output is also used to supply SDMMC blocks, the performance of SD and eMMC access is affected. The second downside is that using this option, the EMI of the SoM is higher. Option (2) solves both of those problems, so implement it here. In this case, the PLL4_P is no longer limited and can be operated faster, at 100 MHz, which improves SDMMC performance (read performance is improved from ~41 MiB/s to ~57 MiB/s with dd if=/dev/mmcblk1 of=/dev/null bs=64M count=1). The EMI interference also decreases. Signed-off-by: Marek Vasut <marex@denx.de> Cc: Alexandre Torgue <alexandre.torgue@foss.st.com> Cc: Christophe Roullier <christophe.roullier@foss.st.com> Cc: Gabriel Fernandez <gabriel.fernandez@foss.st.com> Cc: Patrice Chotard <patrice.chotard@foss.st.com> Cc: Patrick Delaunay <patrick.delaunay@foss.st.com> Cc: Stephen Boyd <sboyd@kernel.org> Cc: linux-clk@vger.kernel.org Cc: linux-stm32@st-md-mailman.stormreply.com To: linux-arm-kernel@lists.infradead.org Tested-by: Johann Neuhauser <jneuhauser@dh-electronics.com> Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
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.