SD_EMMC_START
writel(start, host->regs + SD_EMMC_START);
writel(0, host->regs + SD_EMMC_START);
writel(start, host->regs + SD_EMMC_START);
writel(0, host->regs + SD_EMMC_START);
u32 start = readl(host->regs + SD_EMMC_START);