On Wednesday, March 27, 2013, Grant Grundler wrote: > Last year Seungwon Jeon (Samsung) fixed a bug in CLKDIV computation. For easily identifying, it would be good to point the commit id and subject. > But when debugging a related issue (http://crbug.com/221828) I found It is not easy to catch up issue in your site. What problem is bothering you? Could you describe the problem and conditions you have found? Thanks, Seungwon Jeon > the code unreadable. This rewrite simplifies the computation and > explains each step. > > Signed-off-by: Grant Grundler <grundler@xxxxxxxxxxxx> > --- > Tested on Samsung Series 3 Chromebook (exynos 5250 chipset) using > ChromeOS 3.4 kernel (not 3.9-rc3 which this patch is based against). > > I've written a test program to confirm this patch generates the > same correct values and will share that separately. > > drivers/mmc/host/dw_mmc.c | 22 +++++++++++++++------- > 1 file changed, 15 insertions(+), 7 deletions(-) > > > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c > index 9834221..6fdf55b 100644 > --- a/drivers/mmc/host/dw_mmc.c > +++ b/drivers/mmc/host/dw_mmc.c > @@ -631,14 +631,22 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit) > > if (slot->clock != host->current_speed || force_clkinit) { > div = host->bus_hz / slot->clock; > - if (host->bus_hz % slot->clock && host->bus_hz > slot->clock) > - /* > - * move the + 1 after the divide to prevent > - * over-clocking the card. > + if (host->bus_hz > slot->clock) { > + /* don't overclock due to integer math losses */ > + if ((div * slot->clock) < host->bus_hz) > + div++; > + > + /* don't overclock due to resolution of HW */ > + if (div & 1) > + div++; > + > + /* See 6.2.3 CLKDIV in "Mobile Storage Host Databook" > + * Look for dwc_mobile_storage_db.pdf from Synopsys. > + * CLKDIV value 0 means divisor 1, val 1 -> 2, ... > */ > - div += 1; > - > - div = (host->bus_hz != slot->clock) ? DIV_ROUND_UP(div, 2) : 0; > + div /= 2; > + } else > + div = 0; /* use bus_hz */ > > dev_info(&slot->mmc->class_dev, > "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ" > -- > 1.8.1.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-mmc" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
