Re: [PATCH V2 2/3] mmc: dw_mmc: Support voltage changes

Bartlomiej Zolnierkiewicz
2014-09-29T12:50:04Z

Hi,

On Friday, August 29, 2014 01:43:16 PM Ulf Hansson wrote:
> On 25 August 2014 22:59, Doug Anderson <dianders@google.com> wrote:
> > Ulf,
> >
> > On Mon, Aug 25, 2014 at 1:31 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> >> On 22 August 2014 22:38, Doug Anderson <dianders@google.com> wrote:
> >>> Ulf,
> >>>
> >>> On Fri, Aug 22, 2014 at 8:35 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> >>>> On 22 August 2014 15:47, Yuvaraj Kumar C D <yuvaraj.cd@gmail.com> wrote:
> >>>>> From: Doug Anderson <dianders@chromium.org>
> >>>>>
> >>>>> For UHS cards we need the ability to switch voltages from 3.3V to
> >>>>> 1.8V. Add support to the dw_mmc driver to handle this. Note that
> >>>>> dw_mmc needs a little bit of extra code since the interface needs a
> >>>>> special bit programmed to the CMD register while CMD11 is progressing.
> >>>>> This means adding a few extra states to the state machine to track.
> >>>>>
> >>>>> Signed-off-by: Doug Anderson <dianders@chromium.org>
> >>>>> Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd@samsung.com>
> >>>>> ---
> >>>>> changes since v1:
> >>>>> 1. Added error message and return error in case of regulator_set_voltage() fail.
> >>>>> 2. changed dw_mci_cmd_interrupt(host,pending | SDMMC_INT_CMD_DONE)
> >>>>> to dw_mci_cmd_interrupt(host,pending).
> >>>>> 3. Removed unnecessary comments.
> >>>>>
> >>>>> drivers/mmc/host/dw_mmc.c | 134 +++++++++++++++++++++++++++++++++++++++++---
> >>>>> drivers/mmc/host/dw_mmc.h | 5 +-
> >>>>> include/linux/mmc/dw_mmc.h | 2 +
> >>>>> 3 files changed, 131 insertions(+), 10 deletions(-)
> >>>>>
> >>>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> >>>>> index aadb0d6..f20b4b8 100644
> >>>>> --- a/drivers/mmc/host/dw_mmc.c
> >>>>> +++ b/drivers/mmc/host/dw_mmc.c
> >>>>> @@ -29,6 +29,7 @@
> >>>>> #include <linux/irq.h>
> >>>>> #include <linux/mmc/host.h>
> >>>>> #include <linux/mmc/mmc.h>
> >>>>> +#include <linux/mmc/sd.h>
> >>>>> #include <linux/mmc/sdio.h>
> >>>>> #include <linux/mmc/dw_mmc.h>
> >>>>> #include <linux/bitops.h>
> >>>>> @@ -234,10 +235,13 @@ err:
> >>>>> }
> >>>>> #endif /* defined(CONFIG_DEBUG_FS) */
> >>>>>
> >>>>> +static void mci_send_cmd(struct dw_mci_slot *slot, u32 cmd, u32 arg);
> >>>>> +
> >>>>> static u32 dw_mci_prepare_command(struct mmc_host *mmc, struct mmc_command *cmd)
> >>>>> {
> >>>>> struct mmc_data *data;
> >>>>> struct dw_mci_slot *slot = mmc_priv(mmc);
> >>>>> + struct dw_mci *host = slot->host;
> >>>>> const struct dw_mci_drv_data *drv_data = slot->host->drv_data;
> >>>>> u32 cmdr;
> >>>>> cmd->error = -EINPROGRESS;
> >>>>> @@ -253,6 +257,31 @@ static u32 dw_mci_prepare_command(struct mmc_host *mmc, struct mmc_command *cmd)
> >>>>> else if (cmd->opcode != MMC_SEND_STATUS && cmd->data)
> >>>>> cmdr |= SDMMC_CMD_PRV_DAT_WAIT;
> >>>>>
> >>>>> + if (cmd->opcode == SD_SWITCH_VOLTAGE) {
> >>>>> + u32 clk_en_a;
> >>>>> +
> >>>>> + /* Special bit makes CMD11 not die */
> >>>>> + cmdr |= SDMMC_CMD_VOLT_SWITCH;
> >>>>> +
> >>>>> + /* Change state to continue to handle CMD11 weirdness */
> >>>>> + WARN_ON(slot->host->state != STATE_SENDING_CMD);
> >>>>> + slot->host->state = STATE_SENDING_CMD11;
> >>>>> +
> >>>>> + /*
> >>>>> + * We need to disable clock stop while doing voltage switch
> >>>>> + * according to Voltage Switch Normal Scenario.
> >>>>> + * It's assumed that by the next time the CLKENA is updated
> >>>>> + * (when we set the clock next) that the voltage change will
> >>>>> + * be over, so we don't bother setting any bits to synchronize
> >>>>> + * with dw_mci_setup_bus().
> >>>>> + */
> >>>>
> >>>> I don't know the details about the dw_mmc controller, but normally a
> >>>> host driver is expected to gate the clock from it's ->set_ios
> >>>> callback, when the clk frequency are set to 0.
> >>>>
> >>>> Could you elaborate on why dw_mmc can't do that, but need to handle
> >>>> this from here?
> >>>
> >>> Let's see, it's been a while since I wrote this...
> >>>
> >>>
> >>> So dw_mmc has a special feature where the controller itself will
> >>> automatically stop the MMC Card clock when nothing is going on. This
> >>> is called "low power" mode. I'm not super familiar with other MMC
> >>> drivers, I get the impression that this is a special dw_mmc feature
> >>> and not common to other controllers. I think other drivers have
> >>> aggressive runtime PM to get similar power savings.
> >>
> >> I see.
> >>
> >> I am familiar with such "low power" mode features, there are certainly
> >> other controllers supporting such as well. My experience tells me,
> >> it's hard to get things right for all corner cases. The voltage switch
> >> behaviour is just one of these, then you have SDIO irq etc.
> >>
> >> Instead of using the controller HW, yes you may implement clock gating
> >> through runtime PM in the host driver.
> >>
> >>>
> >>> The dw_mmc auto clock gating can wreck total havoc on the voltage
> >>> change procedure, since part of the way that the host and card
> >>> communicate is that the host is supposed to stop its clock when it
> >>> gets to a certain phase of the voltage switch sequence. If the
> >>> controller is stopping the clock for us then it can confuse the card.
> >>>
> >>> The dw_mmc manual says that before starting a voltage change you must
> >>> turn off low power mode. That's what we're doing here.
> >>>
> >>>
> >>> The comment above refers to the fact dw_mci_setup_bus() will
> >>> unconditionally turn low power mode back on for us when called with a
> >>> non-zero clock. If dw_mci_setup_bus() might be called with a non-zero
> >>> clock during the voltage change then this would be disaster (low power
> >>> mode would be back on!). ...but the clock will always be zero during
> >>> the voltage change and when it's finally non-zero then it's the last
> >>> stage of the voltage change and we can go back to low power mode.
> >>>
> >>>
> >>> Possibly the above was not super clear from the comment (even for
> >>> those familiar with the oddities of dw_mmc). If you want me to try to
> >>> rewrite the comment, let me know.
> >>
> >> I appreciate an updated comment, it's nice to know what goes on. :-)
> >
> > OK, how about:
> >
> > /*
> > * We need to disable low power mode (automatic clock stop)
> > * while doing voltage switch so we don't confuse the card,
> > * since stopping the clock is a specific part of the UHS
> > * voltage change dance.
> > *
> > * Note that low power mode (SDMMC_CLKEN_LOW_PWR) will be
> > * unconditionally turned back on in dw_mci_setup_bus() if it's
> > * ever called with a non-zero clock. That shouldn't happen
> > * until the voltage change is all done.
> > */
> >
> > Yuvaraj: can you include that in the next patch set you send out?
>
> Thanks! Applied for next!
>
> I took the liberty to change to the clarified comment from Doug above.

This patch casuses a boot hang during regulators initizalization on
Exynos5420 Arndale Octa board.

The kernel config used can was posted in other thread:
http://www.mail-archive.com/linux-samsung-soc@vger.kernel.org/msg37210.html

IOW I need to revert both

"mmc: dw_mmc: Support voltage changes"

and

"mmc: dw_mmc: use mmc_regulator_get_supply to handle regulators"

patches to make next branch of mmc-uh tree work on my setup.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics