mmc: dw_mmc: Fix the DTO timeout calculation

Just like the CTO timeout calculation introduced recently, the DTO
timeout calculation was incorrect.  It used "bus_hz" but, as far as I
can tell, it's supposed to use the card clock.  Let's account for the
div value, which is documented as 2x the value stored in the register,
or 1 if the register is 0.

NOTE: This was likely not terribly important until commit 16a34574c6
("mmc: dw_mmc: remove the quirks flags") landed because "DIV" is
documented on Rockchip SoCs (the ones that used to define the quirk)
to always be 0 or 1.  ...and, in fact, it's documented to only be 1
with EMMC in 8-bit DDR52 mode.  Thus before the quirk was applied to
everyone it was mostly OK to ignore the DIV value.

I haven't personally observed any problems that are fixed by this
patch but I also haven't tested this anywhere with a DIV other an 0.
AKA: this problem was found simply by code inspection and I have no
failing test cases that are fixed by it.  Presumably this could fix
real bugs for someone out there, though.

Fixes: 16a34574c6 ("mmc: dw_mmc: remove the quirks flags")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc.c

@@ -1936,10 +1936,15 @@ static int dw_mci_data_complete(struct dw_mci *host, struct mmc_data *data)
 static void dw_mci_set_drto(struct dw_mci *host)
 {
 	unsigned int drto_clks;
+	unsigned int drto_div;
 	unsigned int drto_ms;
 
 	drto_clks = mci_readl(host, TMOUT) >> 8;
-	drto_ms = DIV_ROUND_UP(drto_clks, host->bus_hz / 1000);
+	drto_div = (mci_readl(host, CLKDIV) & 0xff) * 2;
+	if (drto_div == 0)
+		drto_div = 1;
+	drto_ms = DIV_ROUND_UP(MSEC_PER_SEC * drto_clks * drto_div,
+			       host->bus_hz);
 
 	/* add a bit spare time */
 	drto_ms += 10;