Re: [PATCH v6 4/4] dmaengine: pl330: Don't require irq-safe runtime PM

[Ulf Hansson <ulf.hansson@linaro.org>]

On 24 January 2017 at 10:27, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> This patch replaces irq-safe runtime PM with non-irq-safe version based on
> the new approach. Existing, irq-safe runtime PM implementation for PL330 was
> not bringing much benefits of its own - only clocks were enabled/disabled.
>
> Till now non-irq-safe runtime PM implementation was only possible by calling
> pm_runtime_get/put functions from alloc/free_chan_resources. All other DMA
> engine API functions cannot be called from a context, which permits sleeping.
> Such implementation, in practice would result in keeping DMA controller's
> device active almost all the time, because most of the slave device drivers
> (DMA engine clients) acquire DMA channel in their probe() function and
> released it during driver removal.
>
> This patch provides a new, different approach. It is based on an observation
> that there can be only one slave device using each DMA channel. PL330 hardware
> always has dedicated channels for each peripheral device. Using recently
> introduced device dependencies (links) infrastructure one can ensure proper
> runtime PM state of PL330 DMA controller basing on the runtime PM state of
> the slave device.
>
> In this approach in pl330_alloc_chan_resources() function a new dependency
> is being created between PL330 DMA controller device (as a supplier) and
> given slave device (as a consumer). This way PL330 DMA controller device
> runtime active counter is increased when the slave device is resumed and
> decreased the same time when given slave device is put to suspend. This way
> it has been ensured to keep PL330 DMA controller runtime active if there is
> an active used of any of its DMA channels. Slave device pointer is initially
> stored in per-channel data in of_dma_xlate callback. This is similar to what
> has been already implemented in Exynos IOMMU driver in commit 2f5f44f205cc95
> ("iommu/exynos: Use device dependency links to control runtime pm").
>
> If slave device doesn't implement runtime PM or keeps device runtime active
> all the time, then PL330 DMA controller will be runtime active all the time
> when channel is being allocated. The goal is however to have runtime PM

I would remove everything after "The goal is however.."  from this section.

Instead, what I think is important to state (may be added in the first
section in the change log) is however another limitation with irq-safe
runtime PM. That is, it may prevent the generic PM domain (genpd) from
being powered off, particularly in cases when the genpd doesn't have
the GENPD_FLAG_IRQ_SAFE set.

> added to all devices in the system, because it lets respective power
> domains to be turned off, what gives the best results in terms of power
> saving.
>
> If one requests memory-to-memory channel, runtime active counter is
> increased unconditionally. This might be a drawback of this approach, but
> PL330 is not really used for memory-to-memory operations due to poor
> performance in such operations compared to the CPU.
>
> Introducing non-irq-safe runtime power management finally allows to turn off
> audio power domain on Exynos5 SoCs.
>
> Removal of irq-safe runtime PM is based on the revert of the following
> commits:
> 1. commit 5c9e6c2b2ba3 "dmaengine: pl330: fix runtime pm support"
> 2. commit 81cc6edc0870 "dmaengine: pl330: Fix hang on dmaengine_terminate_all
>    on certain boards"
> 3. commit ae43b3289186 "ARM: 8202/1: dmaengine: pl330: Add runtime Power
>    Management support v12"
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
> Acked-by: Arnd Bergmann <arnd@arndb.de>

Nice work!

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe

> ---
>  drivers/dma/pl330.c | 166 +++++++++++++++++++++-------------------------------
>  1 file changed, 66 insertions(+), 100 deletions(-)
>
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index c77a3494659c..dff7228198f6 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -268,9 +268,6 @@ enum pl330_byteswap {
>
>  #define NR_DEFAULT_DESC        16
>
> -/* Delay for runtime PM autosuspend, ms */
> -#define PL330_AUTOSUSPEND_DELAY 20
> -
>  /* Populated by the PL330 core driver for DMA API driver's info */
>  struct pl330_config {
>         u32     periph_id;
> @@ -449,8 +446,8 @@ struct dma_pl330_chan {
>         bool cyclic;
>
>         /* for runtime pm tracking */
> -       bool active;
>         struct device *slave;
> +       struct device_link *slave_link;
>  };
>
>  struct pl330_dmac {
> @@ -2008,7 +2005,6 @@ static void pl330_tasklet(unsigned long data)
>         struct dma_pl330_chan *pch = (struct dma_pl330_chan *)data;
>         struct dma_pl330_desc *desc, *_dt;
>         unsigned long flags;
> -       bool power_down = false;
>
>         spin_lock_irqsave(&pch->lock, flags);
>
> @@ -2023,18 +2019,10 @@ static void pl330_tasklet(unsigned long data)
>         /* Try to submit a req imm. next to the last completed cookie */
>         fill_queue(pch);
>
> -       if (list_empty(&pch->work_list)) {
> -               spin_lock(&pch->thread->dmac->lock);
> -               _stop(pch->thread);
> -               spin_unlock(&pch->thread->dmac->lock);
> -               power_down = true;
> -               pch->active = false;
> -       } else {
> -               /* Make sure the PL330 Channel thread is active */
> -               spin_lock(&pch->thread->dmac->lock);
> -               _start(pch->thread);
> -               spin_unlock(&pch->thread->dmac->lock);
> -       }
> +       /* Make sure the PL330 Channel thread is active */
> +       spin_lock(&pch->thread->dmac->lock);
> +       _start(pch->thread);
> +       spin_unlock(&pch->thread->dmac->lock);
>
>         while (!list_empty(&pch->completed_list)) {
>                 struct dmaengine_desc_callback cb;
> @@ -2047,13 +2035,6 @@ static void pl330_tasklet(unsigned long data)
>                 if (pch->cyclic) {
>                         desc->status = PREP;
>                         list_move_tail(&desc->node, &pch->work_list);
> -                       if (power_down) {
> -                               pch->active = true;
> -                               spin_lock(&pch->thread->dmac->lock);
> -                               _start(pch->thread);
> -                               spin_unlock(&pch->thread->dmac->lock);
> -                               power_down = false;
> -                       }
>                 } else {
>                         desc->status = FREE;
>                         list_move_tail(&desc->node, &pch->dmac->desc_pool);
> @@ -2068,12 +2049,6 @@ static void pl330_tasklet(unsigned long data)
>                 }
>         }
>         spin_unlock_irqrestore(&pch->lock, flags);
> -
> -       /* If work list empty, power down */
> -       if (power_down) {
> -               pm_runtime_mark_last_busy(pch->dmac->ddma.dev);
> -               pm_runtime_put_autosuspend(pch->dmac->ddma.dev);
> -       }
>  }
>
>  static struct dma_chan *of_dma_pl330_xlate(struct of_phandle_args *dma_spec,
> @@ -2105,11 +2080,63 @@ static struct dma_chan *of_dma_pl330_xlate(struct of_phandle_args *dma_spec,
>         return dma_get_slave_channel(&pl330->peripherals[chan_id].chan);
>  }
>
> +static int pl330_add_slave_pm_link(struct pl330_dmac *pl330,
> +                                  struct dma_pl330_chan *pch)
> +{
> +       int i;
> +
> +       /* No slave device means memory-to-memory channels */
> +       if (!pch->slave)
> +               return pm_runtime_get_sync(pl330->ddma.dev);
> +
> +       /*
> +        * No additional locking is needed, {alloc,free}_chan_resources
> +        * are called under dma_list_mutex in dmaengine core
> +        */
> +       for (i = 0; i < pl330->num_peripherals; i++) {
> +               if (pl330->peripherals[i].slave == pch->slave &&
> +                   pl330->peripherals[i].slave_link) {
> +                       pch->slave_link = pl330->peripherals[i].slave_link;
> +                       return 0;
> +               }
> +       }
> +
> +       pch->slave_link = device_link_add(pch->slave, pl330->ddma.dev,
> +                                      DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE);
> +       if (!pch->slave_link)
> +               return -ENODEV;
> +
> +       return 0;
> +}
> +
> +static void pl330_del_slave_pm_link(struct pl330_dmac *pl330,
> +                                   struct dma_pl330_chan *pch)
> +{
> +       struct device_link *link = pch->slave_link;
> +       int i, count = 0;
> +
> +       if (!pch->slave)
> +               pm_runtime_put(pl330->ddma.dev);
> +
> +       for (i = 0; i < pl330->num_peripherals; i++)
> +               if (pl330->peripherals[i].slave_link == link)
> +                       count++;
> +
> +       pch->slave_link = NULL;
> +       if (count == 1)
> +               device_link_del(link);
> +}
> +
>  static int pl330_alloc_chan_resources(struct dma_chan *chan)
>  {
>         struct dma_pl330_chan *pch = to_pchan(chan);
>         struct pl330_dmac *pl330 = pch->dmac;
>         unsigned long flags;
> +       int ret;
> +
> +       ret = pl330_add_slave_pm_link(pl330, pch);
> +       if (ret < 0)
> +               return ret;
>
>         spin_lock_irqsave(&pl330->lock, flags);
>
> @@ -2119,6 +2146,7 @@ static int pl330_alloc_chan_resources(struct dma_chan *chan)
>         pch->thread = pl330_request_channel(pl330);
>         if (!pch->thread) {
>                 spin_unlock_irqrestore(&pl330->lock, flags);
> +               pl330_del_slave_pm_link(pl330, pch);
>                 return -ENOMEM;
>         }
>
> @@ -2160,9 +2188,7 @@ static int pl330_terminate_all(struct dma_chan *chan)
>         unsigned long flags;
>         struct pl330_dmac *pl330 = pch->dmac;
>         LIST_HEAD(list);
> -       bool power_down = false;
>
> -       pm_runtime_get_sync(pl330->ddma.dev);
>         spin_lock_irqsave(&pch->lock, flags);
>         spin_lock(&pl330->lock);
>         _stop(pch->thread);
> @@ -2171,8 +2197,6 @@ static int pl330_terminate_all(struct dma_chan *chan)
>         pch->thread->req[0].desc = NULL;
>         pch->thread->req[1].desc = NULL;
>         pch->thread->req_running = -1;
> -       power_down = pch->active;
> -       pch->active = false;
>
>         /* Mark all desc done */
>         list_for_each_entry(desc, &pch->submitted_list, node) {
> @@ -2189,10 +2213,6 @@ static int pl330_terminate_all(struct dma_chan *chan)
>         list_splice_tail_init(&pch->work_list, &pl330->desc_pool);
>         list_splice_tail_init(&pch->completed_list, &pl330->desc_pool);
>         spin_unlock_irqrestore(&pch->lock, flags);
> -       pm_runtime_mark_last_busy(pl330->ddma.dev);
> -       if (power_down)
> -               pm_runtime_put_autosuspend(pl330->ddma.dev);
> -       pm_runtime_put_autosuspend(pl330->ddma.dev);
>
>         return 0;
>  }
> @@ -2210,7 +2230,6 @@ static int pl330_pause(struct dma_chan *chan)
>         struct pl330_dmac *pl330 = pch->dmac;
>         unsigned long flags;
>
> -       pm_runtime_get_sync(pl330->ddma.dev);
>         spin_lock_irqsave(&pch->lock, flags);
>
>         spin_lock(&pl330->lock);
> @@ -2218,8 +2237,6 @@ static int pl330_pause(struct dma_chan *chan)
>         spin_unlock(&pl330->lock);
>
>         spin_unlock_irqrestore(&pch->lock, flags);
> -       pm_runtime_mark_last_busy(pl330->ddma.dev);
> -       pm_runtime_put_autosuspend(pl330->ddma.dev);
>
>         return 0;
>  }
> @@ -2232,7 +2249,6 @@ static void pl330_free_chan_resources(struct dma_chan *chan)
>
>         tasklet_kill(&pch->task);
>
> -       pm_runtime_get_sync(pch->dmac->ddma.dev);
>         spin_lock_irqsave(&pl330->lock, flags);
>
>         pl330_release_channel(pch->thread);
> @@ -2242,19 +2258,17 @@ static void pl330_free_chan_resources(struct dma_chan *chan)
>                 list_splice_tail_init(&pch->work_list, &pch->dmac->desc_pool);
>
>         spin_unlock_irqrestore(&pl330->lock, flags);
> -       pm_runtime_mark_last_busy(pch->dmac->ddma.dev);
> -       pm_runtime_put_autosuspend(pch->dmac->ddma.dev);
> +
> +       pl330_del_slave_pm_link(pl330, pch);
>  }
>
>  static int pl330_get_current_xferred_count(struct dma_pl330_chan *pch,
>                                            struct dma_pl330_desc *desc)
>  {
>         struct pl330_thread *thrd = pch->thread;
> -       struct pl330_dmac *pl330 = pch->dmac;
>         void __iomem *regs = thrd->dmac->base;
>         u32 val, addr;
>
> -       pm_runtime_get_sync(pl330->ddma.dev);
>         val = addr = 0;
>         if (desc->rqcfg.src_inc) {
>                 val = readl(regs + SA(thrd->id));
> @@ -2263,8 +2277,6 @@ static int pl330_get_current_xferred_count(struct dma_pl330_chan *pch,
>                 val = readl(regs + DA(thrd->id));
>                 addr = desc->px.dst_addr;
>         }
> -       pm_runtime_mark_last_busy(pch->dmac->ddma.dev);
> -       pm_runtime_put_autosuspend(pl330->ddma.dev);
>
>         /* If DMAMOV hasn't finished yet, SAR/DAR can be zero */
>         if (!val)
> @@ -2350,16 +2362,6 @@ static void pl330_issue_pending(struct dma_chan *chan)
>         unsigned long flags;
>
>         spin_lock_irqsave(&pch->lock, flags);
> -       if (list_empty(&pch->work_list)) {
> -               /*
> -                * Warn on nothing pending. Empty submitted_list may
> -                * break our pm_runtime usage counter as it is
> -                * updated on work_list emptiness status.
> -                */
> -               WARN_ON(list_empty(&pch->submitted_list));
> -               pch->active = true;
> -               pm_runtime_get_sync(pch->dmac->ddma.dev);
> -       }
>         list_splice_tail_init(&pch->submitted_list, &pch->work_list);
>         spin_unlock_irqrestore(&pch->lock, flags);
>
> @@ -2787,44 +2789,12 @@ static irqreturn_t pl330_irq_handler(int irq, void *data)
>         BIT(DMA_SLAVE_BUSWIDTH_8_BYTES)
>
>  /*
> - * Runtime PM callbacks are provided by amba/bus.c driver.
> - *
> - * It is assumed here that IRQ safe runtime PM is chosen in probe and amba
> - * bus driver will only disable/enable the clock in runtime PM callbacks.
> + * Runtime PM callbacks are provided by amba/bus.c driver, system sleep
> + * suspend/resume is implemented by generic helpers, which use existing
> + * runtime PM callbacks.
>   */
> -static int __maybe_unused pl330_suspend(struct device *dev)
> -{
> -       struct amba_device *pcdev = to_amba_device(dev);
> -
> -       pm_runtime_disable(dev);
> -
> -       if (!pm_runtime_status_suspended(dev)) {
> -               /* amba did not disable the clock */
> -               amba_pclk_disable(pcdev);
> -       }
> -       amba_pclk_unprepare(pcdev);
> -
> -       return 0;
> -}
> -
> -static int __maybe_unused pl330_resume(struct device *dev)
> -{
> -       struct amba_device *pcdev = to_amba_device(dev);
> -       int ret;
> -
> -       ret = amba_pclk_prepare(pcdev);
> -       if (ret)
> -               return ret;
> -
> -       if (!pm_runtime_status_suspended(dev))
> -               ret = amba_pclk_enable(pcdev);
> -
> -       pm_runtime_enable(dev);
> -
> -       return ret;
> -}
> -
> -static SIMPLE_DEV_PM_OPS(pl330_pm, pl330_suspend, pl330_resume);
> +static SIMPLE_DEV_PM_OPS(pl330_pm, pm_runtime_force_suspend,
> +                        pm_runtime_force_resume);
>
>  static int
>  pl330_probe(struct amba_device *adev, const struct amba_id *id)
> @@ -2977,11 +2947,7 @@ static int __maybe_unused pl330_resume(struct device *dev)
>                 pcfg->data_buf_dep, pcfg->data_bus_width / 8, pcfg->num_chan,
>                 pcfg->num_peri, pcfg->num_events);
>
> -       pm_runtime_irq_safe(&adev->dev);
> -       pm_runtime_use_autosuspend(&adev->dev);
> -       pm_runtime_set_autosuspend_delay(&adev->dev, PL330_AUTOSUSPEND_DELAY);
> -       pm_runtime_mark_last_busy(&adev->dev);
> -       pm_runtime_put_autosuspend(&adev->dev);
> +       pm_runtime_put(&adev->dev);
>
>         return 0;
>  probe_err3:
> --
> 1.9.1
>