On 08/26/2013 01:34 PM, Seungwon Jeon wrote:
> 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'?
Right, Dw-mmc controller can use the Low-power mode.
This mode is functionality like clock-gating. Well, i didn't know what benefit we get, if set to 0.
Best Regards,
Jaehoon Chung
>
>> + } 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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