On Fri, August 23, 2013, Doug Anderson wrote:
> Previously the dw_mmc driver would ignore any requests to disable the
> card's clock. This doesn't seem like a good thing in general, but had
> one extra bad side effect in the following situtation:
> * mmc core would set clk to 400kHz at boot time while initting
> * mmc core would set clk to 0 since no card, but it would be ignored.
> * suspend to ram and resume; clocks in the dw_mmc IP block are now 0
> but dw_mmc thinks that they're 400kHz (it ignored the set to 0).
> * insert card
> * mmc core would set clk to 400kHz which would be considered a no-op.
>
> Note that if there is no card in the slot and we do a suspend/resume
> cycle, we _do_ still end up with differences in a dw_mmc register
> dump, but the differences are clock related and we've got the clock
> disabled both before and after, so this should be OK.
>
> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> ---
> Changes in v6:
> - Replaces previous pathes that ensured saving/restoring clocks.
>
> drivers/mmc/host/dw_mmc.c | 21 +++++++++++----------
> 1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index ee5f167..f6c7545 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -635,7 +635,11 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
> u32 div;
> u32 clk_en_a;
>
> - if (slot->clock != host->current_speed || force_clkinit) {
> + if (slot->clock == 0) {
> + mci_writel(host, CLKENA, 0);
> + mci_send_cmd(slot,
> + SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
Basically dw_mmc driver uses host's low power mode(auto clock gating)
So, how about keeping origin code rather than programming clock setting to '0'?
> + } else if (slot->clock != host->current_speed || force_clkinit) {
And then, if condition('slot->clock is not zero') is added in order to allow to set clock,
print messages which Jaehoon pointed would be solved.
Thanks,
Seungwon Jeon
> div = host->bus_hz / slot->clock;
> if (host->bus_hz % slot->clock && host->bus_hz > slot->clock)
> /*
> @@ -675,9 +679,8 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
> /* inform CIU */
> mci_send_cmd(slot,
> SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
> -
> - host->current_speed = slot->clock;
> }
> + host->current_speed = slot->clock;
>
> /* Set the current slot bus width */
> mci_writel(host, CTYPE, (slot->ctype << slot->id));
> @@ -807,13 +810,11 @@ static void dw_mci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
>
> mci_writel(slot->host, UHS_REG, regs);
>
> - if (ios->clock) {
> - /*
> - * Use mirror of ios->clock to prevent race with mmc
> - * core ios update when finding the minimum.
> - */
> - slot->clock = ios->clock;
> - }
> + /*
> + * Use mirror of ios->clock to prevent race with mmc
> + * core ios update when finding the minimum.
> + */
> + slot->clock = ios->clock;
>
> if (drv_data && drv_data->set_ios)
> drv_data->set_ios(slot->host, ios);
> --
> 1.8.3
>
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