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  SOCFPGA Documentation for U-Boot and SPL
  --------------------------------------------
  
  This README is about U-Boot and SPL support for Altera's ARM Cortex-A9MPCore
  based SOCFPGA. To know more about the hardware itself, please refer to
  www.altera.com.
  
  
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  socfpga_dw_mmc
  --------------------------------------------
  Here are macro and detailed configuration required to enable DesignWare SDMMC
  controller support within SOCFPGA
  
  #define CONFIG_MMC
  -> To enable the SD MMC framework support
  
  #define CONFIG_SDMMC_BASE		(SOCFPGA_SDMMC_ADDRESS)
  -> The base address of CSR register for DesignWare SDMMC controller
  
  #define CONFIG_GENERIC_MMC
  -> Enable the generic MMC driver
  
  #define CONFIG_SYS_MMC_MAX_BLK_COUNT	256
  -> Using smaller max blk cnt to avoid flooding the limited stack in OCRAM
  
  #define CONFIG_DWMMC
  -> Enable the common DesignWare SDMMC controller framework
  
  #define CONFIG_SOCFPGA_DWMMC
  -> Enable the SOCFPGA specific driver for DesignWare SDMMC controller
  
  #define CONFIG_SOCFPGA_DWMMC_FIFO_DEPTH		1024
  -> The FIFO depth for SOCFPGA DesignWare SDMMC controller
  
  #define CONFIG_SOCFPGA_DWMMC_DRVSEL	3
  -> Phase-shifted clock of sdmmc_clk for controller to drive command and data to
  the card to meet hold time requirements. SD clock is running at 50MHz and
  drvsel is set to shift 135 degrees (3 * 45 degrees). With that, the hold time
  is 135 / 360 * 20ns = 7.5ns.
  
  #define CONFIG_SOCFPGA_DWMMC_SMPSEL	0
  -> Phase-shifted clock of sdmmc_clk used to sample the command and data from
  the card
  
  #define CONFIG_SOCFPGA_DWMMC_BUS_WIDTH	4
  -> Bus width of data line which either 1, 4 or 8 and based on board routing.
  
  #define CONFIG_SOCFPGA_DWMMC_BUS_HZ	50000000
  -> The clock rate to controller. Do note the controller have a wrapper which
  divide the clock from PLL by 4.