Re: [PATCH 3/3] mmc: omap_hsmmc: switch to 1-bit before turning off clocks if interrupts expected.

[NeilBrown]

On Wed, 28 Jan 2015 21:18:40 +0100 Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:

> On 28 January 2015 at 00:35, NeilBrown <neilb@xxxxxxx> wrote:
> > According to section 7.1.2 of
> >
> > http://www.sandisk.com/media/File/OEM/Manuals/SD_SDIO_specsv1.pdf
> >
> >     In the case where the interrupt mechanism is used to wake the host while
> >     the card is in a low power state (i.e. no clocks), Both the card and the
> >     host shall be placed into the 1-bit SD mode prior to stopping the clock.
> >
> >
> > This is particularly important for the Marvell "libertas" wifi chip
> > in the GTA04.  While in 4-bit mode it will only signal an interrupt
> > when the clock is running (which is why setting CLKEXTFREE is
> > important).
> > In 1-bit mode, the interrupt is asynchronous (explained in OMAP3
> > TRM description of the CIRQ flag to MMCHS_STAT:
> >
> >   In 1-bit mode, interrupt source is asynchronous (can be a source of
> >   asynchronous wakeup).
> >   In 4-bit mode, interrupt source is sampled during the interrupt
> >   cycle.
> >
> > )
> >
> > We cannot simply set 1-bit mode in omap_hsmmc_runtime_suspend
> > as that is called under a spinlock, and setting 1-bit mode requires
> > a sleeping call to the card.
> >
> > So:
> >  - use a work_struct to schedule setting of 1-bit mode
> >  - intro a 'force_narrow' state flag which transitions:
> >      0 -> NARROW_PENDING -> NARROW_FORCED -> 0
> >  - have omap_hsmmc_runtime_suspend fail if interrupts are expected
> >    but bus is not in 1-bit mode.  When it fails it schedules
> >    the work to change the width. and sets NARROW_PENDING
> >  - when the host is claimed, if NARROW_FORCED is set, restore the
> >    4-bit bus
> >  - When the host is released (disable_fclk), if NARROW_FORCED,
> >    then suspend immediately, no autosuspend.  If NARROW_PENDING,
> >    clear that flag as the device has obviously just been used.
> 
> I can't give you more detailed comment about this patch(set) yet. Need
> to think a bit more first.
> 
> Anyway, I have one concern, see comment below.
> 
> >
> > This all allows a graceful and race-free switch to 1-bit mode
> > before switching off the clocks, if interrupts are enabled.
> >
> > With this, I can use my libertas wifi with a 4-bit bus, with
> > interrupts and runtime power-management enabled, and get around
> > 14Mb/sec throughput (which is the best I've seen).
> >
> > Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
> > ---
> >  drivers/mmc/host/omap_hsmmc.c |   55 ++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 53 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> > index f84cfb01716d..91ddebbec8a3 100644
> > --- a/drivers/mmc/host/omap_hsmmc.c
> > +++ b/drivers/mmc/host/omap_hsmmc.c
> > @@ -214,6 +214,10 @@ struct omap_hsmmc_host {
> >         int                     reqs_blocked;
> >         int                     use_reg;
> >         int                     req_in_progress;
> > +       int                     force_narrow;
> > +#define NARROW_PENDING 1
> > +#define NARROW_FORCED  2
> > +       struct work_struct      width_work;
> >         unsigned long           clk_rate;
> >         unsigned int            flags;
> >  #define AUTO_CMD23             (1 << 0)        /* Auto CMD23 support */
> > @@ -1778,12 +1782,43 @@ static void omap_hsmmc_conf_bus_power(struct omap_hsmmc_host *host)
> >         set_sd_bus_power(host);
> >  }
> >
> > +static void omap_hsmmc_width_work(struct work_struct *work)
> > +{
> > +       struct omap_hsmmc_host *host = container_of(work,
> > +                                                   struct omap_hsmmc_host,
> > +                                                   width_work);
> > +       atomic_t noblock;
> > +
> > +       atomic_set(&noblock, 1);
> > +       if (__mmc_claim_host(host->mmc, &noblock)) {
> > +               /* Device active again */
> > +               host->force_narrow = 0;
> > +               return;
> > +       }
> > +       if (host->force_narrow != NARROW_PENDING) {
> > +               /* Someone claimed and released before we got here */
> > +               mmc_release_host(host->mmc);
> > +               return;
> > +       }
> > +       if (sdio_disable_wide(host->mmc->card) == 0)
> > +               host->force_narrow = NARROW_FORCED;
> > +       else
> > +               host->force_narrow = 0;
> > +       mmc_release_host(host->mmc);
> > +}
> > +
> >  static int omap_hsmmc_enable_fclk(struct mmc_host *mmc)
> >  {
> >         struct omap_hsmmc_host *host = mmc_priv(mmc);
> >
> >         pm_runtime_get_sync(host->dev);
> >
> > +       if (host->force_narrow == NARROW_FORCED) {
> > +               if (sdio_enable_4bit_bus(mmc->card) > 0)
> > +                       mmc_set_bus_width(mmc, MMC_BUS_WIDTH_4);
> > +               host->force_narrow = 0;
> > +       }
> > +
> >         return 0;
> >  }
> >
> > @@ -1791,8 +1826,13 @@ static int omap_hsmmc_disable_fclk(struct mmc_host *mmc)
> >  {
> >         struct omap_hsmmc_host *host = mmc_priv(mmc);
> >
> > -       pm_runtime_mark_last_busy(host->dev);
> > -       pm_runtime_put_autosuspend(host->dev);
> > +       if (host->force_narrow == NARROW_FORCED) {
> > +               pm_runtime_put_sync(host->dev);
> > +       } else {
> > +               host->force_narrow = 0;
> > +               pm_runtime_mark_last_busy(host->dev);
> > +               pm_runtime_put_autosuspend(host->dev);
> > +       }
> >
> >         return 0;
> >  }
> > @@ -2024,6 +2064,7 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
> >         host->power_mode = MMC_POWER_OFF;
> >         host->next_data.cookie = 1;
> >         host->pbias_enabled = 0;
> > +       INIT_WORK(&host->width_work, omap_hsmmc_width_work);
> >
> >         ret = omap_hsmmc_gpio_init(mmc, host, pdata);
> >         if (ret)
> > @@ -2311,6 +2352,16 @@ static int omap_hsmmc_runtime_suspend(struct device *dev)
> >         spin_lock_irqsave(&host->irq_lock, flags);
> >         if ((host->mmc->caps & MMC_CAP_SDIO_IRQ) &&
> >             (host->flags & HSMMC_SDIO_IRQ_ENABLED)) {
> > +               if (host->mmc->ios.bus_width != MMC_BUS_WIDTH_1) {
> > +                       /* In 4-bit mode the card need the clock
> > +                        * to deliver interrupts, so it isn't safe
> > +                        * to turn it off.
> > +                        */
> > +                       host->force_narrow = NARROW_PENDING;
> > +                       schedule_work(&host->width_work);
> > +                       ret = -EBUSY;
> > +                       goto abort;
> 
> >From a host driver perspective, don't you think this a bit too much to
> implement to cover this case!?
> 
> I would rather see the host driver to invoke _one_ API provided by the
> mmc core, which takes care of the needed things and also tells the
> host driver whether it's safe to enter runtime PM suspend state or
> not. Could that work?

Since posting the patch I've been thinking along those lines too.  I hadn't
imagined making just a single call from the host driver, but now that I think
about it I don't see why not.  It should definitely work.

I'll re-spin them in the next day or two.

Thanks,
NeilBrown

> 
> > +               }
> >                 /* disable sdio irq handling to prevent race */
> >                 OMAP_HSMMC_WRITE(host->base, ISE, 0);
> >                 OMAP_HSMMC_WRITE(host->base, IE, 0);
> >
> >
> 
> Kind regards
> Uffe

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