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 <grund...@chromium.org>
> ---
> 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
>
> --
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