Re: [PATCH 3/4] mmc: sdio: support switching to 1-bit before turning off clocks

Ulf Hansson
2015-03-23T09:10:23Z

On 24 February 2015 at 03:42, NeilBrown <neilb@suse.de> 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.
>
> )
>
> It is awkward to simply set 1-bit mode in ->runtime_suspend
> as that will call mmc_set_ios which calls ops->set_ios(),
> which will likely call pm_runtime_get_sync(), on the device that
> is currently suspending. This deadlocks.
>
> So:
> - create a work_struct to schedule setting of 1-bit mode
> - introduce an 'sdio_narrowed' state flag which transitions:
> 0 (normal) -> 1 (convert to 1-bit pending) ->
> 2 (have switch to 1-bit mode) -> 0 (normal)
> - create a function mmc_sdio_want_no_clocks() which can be called
> when the driver wants to turn off clocks (presumably after an
> idle timeout). This either succeeds (in 1-bit mode) or fails
> and schedules the work to switch to 1-bit mode.
> - when the host is claimed, if sdio_narrowed is 2, restore the
> 4-bit bus
> - When the host is released, if sdio_narrowed is 1, then some
> caller other than our worker claimed the host first, so
> clear sdio_narrowed.
>
> This all allows a graceful and race-free switch to 1-bit mode
> before switching off the clocks, if SDIO interrupts are enabled.
>
> A host should call mmc_sdio_want_no_clocks() when about to turn off
> clocks if sdio interrupts are enabled, and the ->disable() function
> should not use a timeout (pm_runtime_put_autosuspend) if
> ->sdio_narrowed is 2.
>
> Signed-off-by: NeilBrown <neil@brown.name>

Hi Neil,

Thanks for sending this patchset, and sorry for the delay in response.

Overall I like the approach taken in this patchset, though I have some
questions see below.

> ---
> drivers/mmc/core/core.c | 18 ++++++++++++++----
> drivers/mmc/core/sdio.c | 42 +++++++++++++++++++++++++++++++++++++++++-
> include/linux/mmc/core.h | 2 ++
> include/linux/mmc/host.h | 2 ++
> 4 files changed, 59 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 541c8903dc6b..0258fdf1a03d 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -921,8 +921,14 @@ int __mmc_claim_host(struct mmc_host *host, atomic_t *abort)
> wake_up(&host->wq);
> spin_unlock_irqrestore(&host->lock, flags);
> remove_wait_queue(&host->wq, &wait);
> - if (host->ops->enable && !stop && host->claim_cnt == 1)
> - host->ops->enable(host);
> + if (!stop && host->claim_cnt == 1) {
> + if (host->ops->enable)
> + host->ops->enable(host);
> + if (atomic_read(&host->sdio_narrowed) == 2) {
> + sdio_enable_4bit_bus(host->card);
> + atomic_set(&host->sdio_narrowed, 0);
> + }
> + }
> return stop;
> }
>
> @@ -941,8 +947,12 @@ void mmc_release_host(struct mmc_host *host)
>
> WARN_ON(!host->claimed);
>
> - if (host->ops->disable && host->claim_cnt == 1)
> - host->ops->disable(host);
> + if (host->claim_cnt == 1) {
> + if (atomic_read(&host->sdio_narrowed) == 1)
> + atomic_set(&host->sdio_narrowed, 0);
> + if (host->ops->disable)
> + host->ops->disable(host);
> + }

As omap_hsmmc in currently the only user of the
host_ops->enable|disable() callbacks, I wonder if this approach will
work "race-free" for those hosts that don't implement these callbacks?

Also, I was kind of hoping that we should be able to remove these
host_ops callbacks, when omap_hsmmc has moved away from using them. Do
you think that can be done?

Within this context, I am also reviewing Adrian Hunter's patchset
around "periodic re-tuning" [1] and to me, you guys are sharing a
similar issue.

The host driver's runtime PM suspend callback needs to be able to
notify the mmc core to take some specific actions, and in a
"race-free" manner.

I wonder whether we could have one common solution to that? Do you
think this approach will work for Adrian's "periodic re-tuning" as
well?

>
> spin_lock_irqsave(&host->lock, flags);
> if (--host->claim_cnt) {
> diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
> index 5bc6c7dbbd60..9761e4d5f49b 100644
> --- a/drivers/mmc/core/sdio.c
> +++ b/drivers/mmc/core/sdio.c
> @@ -288,7 +288,7 @@ static int sdio_disable_wide(struct mmc_card *card)
> }
>
>
> -static int sdio_enable_4bit_bus(struct mmc_card *card)
> +int sdio_enable_4bit_bus(struct mmc_card *card)
> {
> int err;
>
> @@ -313,6 +313,45 @@ static int sdio_enable_4bit_bus(struct mmc_card *card)
> return err;
> }
>
> +static void mmc_sdio_width_work(struct work_struct *work)
> +{
> + struct mmc_host *host = container_of(work, struct mmc_host,
> + sdio_width_work);
> + atomic_t noblock;
> +
> + atomic_set(&noblock, 1);
> + if (__mmc_claim_host(host, &noblock))
> + return;
> + if (atomic_read(&host->sdio_narrowed) != 1) {
> + /* Nothing to do */
> + mmc_release_host(host);
> + return;
> + }
> + if (sdio_disable_wide(host->card) == 0)
> + atomic_set(&host->sdio_narrowed, 2);
> + else
> + atomic_set(&host->sdio_narrowed, 0);
> + mmc_release_host(host);
> +}
> +
> +int mmc_sdio_want_no_clocks(struct mmc_host *host)
> +{
> + if (!(host->caps & MMC_CAP_SDIO_IRQ) ||
> + host->ios.bus_width == MMC_BUS_WIDTH_1)
> + /* Safe to turn off clocks */
> + return 1;
> +
> +
> + /* In 4-bit mode the card needs the clock
> + * to deliver interrupts, so it isn't safe
> + * to turn of clocks just yet
> + */
> + atomic_add_unless(&host->sdio_narrowed, 1, 1);
> +
> + schedule_work(&host->sdio_width_work);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(mmc_sdio_want_no_clocks);
>
> /*
> * Test if the card supports high-speed mode and, if so, switch to it.
> @@ -1100,6 +1139,7 @@ int mmc_attach_sdio(struct mmc_host *host)
> goto err;
> }
>
> + INIT_WORK(&host->sdio_width_work, mmc_sdio_width_work);
> /*
> * Detect and init the card.
> */
> diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
> index 160448f920ac..faf6d1be0971 100644
> --- a/include/linux/mmc/core.h
> +++ b/include/linux/mmc/core.h
> @@ -212,4 +212,6 @@ struct device_node;
> extern u32 mmc_vddrange_to_ocrmask(int vdd_min, int vdd_max);
> extern int mmc_of_parse_voltage(struct device_node *np, u32 *mask);
>
> +extern int sdio_enable_4bit_bus(struct mmc_card *card);
> +extern int mmc_sdio_want_no_clocks(struct mmc_host *host);
> #endif /* LINUX_MMC_CORE_H */
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 0c8cbe5d1550..7e6a54c49a15 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -350,6 +350,8 @@ struct mmc_host {
> struct task_struct *sdio_irq_thread;
> bool sdio_irq_pending;
> atomic_t sdio_irq_thread_abort;
> + struct work_struct sdio_width_work;
> + atomic_t sdio_narrowed; /* 1==pending, 2==complete*/
>
> mmc_pm_flag_t pm_flags; /* requested pm features */
>
>
>

Kind regards
Uffe

[1]
[PATCH V3 00/15] mmc: host: Add facility to support re-tuning