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Re: [PATCH v2 4/5] mmc: dw_mmc: Fix the DTO timeout calculation

On 2017/10/13 4:11, Douglas Anderson wrote:
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 16a34574c6ca
("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: 16a34574c6ca ("mmc: dw_mmc: remove the quirks flags")
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

Reviewed-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>


Changes in v2:
- Fix the DTO timeout calculation new for v2

  drivers/mmc/host/dw_mmc.c | 8 +++++++-
  1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index 50148991f30e..6bc87b1385a9 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -1936,10 +1936,16 @@ 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;
+	unsigned long irqflags;
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;