OMAP HSMMC data timeout calculation

[Hebbar, Gururaja]

Hi all,


I am trying to understand data timeout value (dto) calculation done in omap 
hsmmc driver (omap_hsmmc.c)

I summed my understanding & my doubts in below code [GH].

Can someone help me in understanding the code


Thanks in advance.

Regards
Gururaja

static void set_data_timeout(struct omap_hsmmc_host *host,
                             unsigned int timeout_ns,
                             unsigned int timeout_clks)
{
        unsigned int timeout, cycle_ns;
        uint32_t reg, clkd, dto = 0;

        reg = OMAP_HSMMC_READ(host->base, SYSCTL);
        clkd = (reg & CLKD_MASK) >> CLKD_SHIFT;
        if (clkd == 0)
                clkd = 1;

        cycle_ns = 1000000000 / (clk_get_rate(host->fclk) / clkd);
        timeout = timeout_ns / cycle_ns;
        timeout += timeout_clks;

[GH] till here, data time out calculation for the card is calclated in terms of 
host controller clock rate


        if (timeout) {
                while ((timeout & 0x80000000) == 0) {
                        dto += 1;
                        timeout <<= 1;
                }
                dto = 31 - dto;

[GH] what is achieved here?


                timeout <<= 1;
                if (timeout && dto)
                        dto += 1;

[GH] what is achieved here?


                if (dto >= 13)
                        dto -= 13;
                else
                        dto = 0;

[GH] why is 13 subtracted when the value is >13 & if <13, why is it made 0


                if (dto > 14)
                        dto = 14;

[GH] This is done to limit the max value.

        }


        reg &= ~DTO_MASK;
        reg |= dto << DTO_SHIFT;
        OMAP_HSMMC_WRITE(host->base, SYSCTL, reg);
}


Regards
Gururaja