6/22/2012

How to add new clock param for SPI bus in linux build on Qualcomm chipset?

SPI clock parameters are defined in arch/arm/mach-msm/clock-xxxx.c file.


The table for the parameters is like below.


static struct clk_freq_tbl clk_tbl_spi[] = {
F_MND8(10000000, 19, 12, SRC_PLL3, 4, 7, 129),
F_MND8(26000000, 19, 12, SRC_PLL3, 4, 34, 241),
F_END,
};


Clock frequency for SPI bus is determined by M:N:D counter and the information about this is described in clock chapter of software interface manual. The concerned registers are SPI_MD_REG and SPI_NS_REG.


The example vale for 1 Mhz SPI clock is below.


F_MND8(1000000, 19, 12, SRC_PLL3, 4, 1, 185),

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