Re: [PATCH v7 4/5] dma: pl330: add Power Management support

[Ulf Hansson]

On 24 September 2014 15:50, Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> wrote:
> This patch adds both normal PM suspend/resume support and runtime PM
> support to pl330 DMA engine driver.
>
> The runtime power management for pl330 DMA driver allows gating of AMBA
> clock (PDMA) in FSYS clock domain, when the device is not processing any
> requests. This is necessary to enter low power modes on Exynos SoCs
> (e.g. LPA on Exynos4x12 or W-AFTR on Exynos3250).
>
> Runtime PM resuming of the device may happen in atomic context (during
> call device_issue_pending()) so pm_runtime_irq_safe() is used. This will
> lead only to disabling/enabling of the clock but this is sufficient for
> gating the clock and for reducing energy usage.
>
> During system sleep the AMBA bus clock is also unprepared.
>
> Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>

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

Kind regards
Uffe

> ---
>  drivers/dma/pl330.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 90 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index 4839bfa74a10..b123431e62ed 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -27,6 +27,7 @@
>  #include <linux/of.h>
>  #include <linux/of_dma.h>
>  #include <linux/err.h>
> +#include <linux/pm_runtime.h>
>
>  #include "dmaengine.h"
>  #define PL330_MAX_CHAN         8
> @@ -265,6 +266,9 @@ static unsigned cmd_line;
>
>  #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;
> @@ -1958,6 +1962,7 @@ 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);
>
> @@ -1972,10 +1977,17 @@ static void pl330_tasklet(unsigned long data)
>         /* Try to submit a req imm. next to the last completed cookie */
>         fill_queue(pch);
>
> -       /* Make sure the PL330 Channel thread is active */
> -       spin_lock(&pch->thread->dmac->lock);
> -       _start(pch->thread);
> -       spin_unlock(&pch->thread->dmac->lock);
> +       if (list_empty(&pch->work_list)) {
> +               spin_lock(&pch->thread->dmac->lock);
> +               _stop(pch->thread);
> +               spin_unlock(&pch->thread->dmac->lock);
> +               power_down = true;
> +       } else {
> +               /* 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)) {
>                 dma_async_tx_callback callback;
> @@ -1990,6 +2002,12 @@ static void pl330_tasklet(unsigned long data)
>                 if (pch->cyclic) {
>                         desc->status = PREP;
>                         list_move_tail(&desc->node, &pch->work_list);
> +                       if (power_down) {
> +                               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);
> @@ -2004,6 +2022,12 @@ 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);
> +       }
>  }
>
>  bool pl330_filter(struct dma_chan *chan, void *param)
> @@ -2073,6 +2097,7 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned
>
>         switch (cmd) {
>         case DMA_TERMINATE_ALL:
> +               pm_runtime_get_sync(pl330->ddma.dev);
>                 spin_lock_irqsave(&pch->lock, flags);
>
>                 spin_lock(&pl330->lock);
> @@ -2099,10 +2124,15 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned
>                         dma_cookie_complete(&desc->txd);
>                 }
>
> +               if (!list_empty(&pch->work_list))
> +                       pm_runtime_put(pl330->ddma.dev);
> +
>                 list_splice_tail_init(&pch->submitted_list, &pl330->desc_pool);
>                 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);
> +               pm_runtime_put_autosuspend(pl330->ddma.dev);
>                 break;
>         case DMA_SLAVE_CONFIG:
>                 slave_config = (struct dma_slave_config *)arg;
> @@ -2138,6 +2168,7 @@ 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(&pch->lock, flags);
>
>         pl330_release_channel(pch->thread);
> @@ -2147,6 +2178,8 @@ static void pl330_free_chan_resources(struct dma_chan *chan)
>                 list_splice_tail_init(&pch->work_list, &pch->dmac->desc_pool);
>
>         spin_unlock_irqrestore(&pch->lock, flags);
> +       pm_runtime_mark_last_busy(pch->dmac->ddma.dev);
> +       pm_runtime_put_autosuspend(pch->dmac->ddma.dev);
>  }
>
>  static enum dma_status
> @@ -2162,6 +2195,15 @@ 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));
> +               pm_runtime_get_sync(pch->dmac->ddma.dev);
> +       }
>         list_splice_tail_init(&pch->submitted_list, &pch->work_list);
>         spin_unlock_irqrestore(&pch->lock, flags);
>
> @@ -2585,6 +2627,41 @@ static int pl330_dma_device_slave_caps(struct dma_chan *dchan,
>         return 0;
>  }
>
> +/*
> + * Assume that IRQ safe runtime PM is chosen in probe and amba bus driver
> + * will only disable/enable the clock in runtime PM suspend/resume.
> + */
> +static int __maybe_unused pl330_suspend(struct device *dev)
> +{
> +       struct amba_device *pcdev = to_amba_device(dev);
> +       int ret;
> +
> +       ret = pm_runtime_force_suspend(dev);
> +       if (ret)
> +               return ret;
> +
> +       amba_pclk_unprepare(pcdev);
> +
> +       return 0;
> +}
> +
> +static int __maybe_unused pl330_resume(struct device *dev)
> +{
> +       struct amba_device *pcdev = to_amba_device(dev);
> +
> +       amba_pclk_prepare(pcdev);
> +
> +       /*
> +        * TODO: Idea for future. The device should not be woken up after
> +        * system resume if it is not needed. It could stay runtime suspended
> +        * waiting for DMA requests. However for safe suspend and resume we
> +        * forcibly resume the device here.
> +        */
> +       return pm_runtime_force_resume(dev);
> +}
> +
> +static SIMPLE_DEV_PM_OPS(pl330_pm, pl330_suspend, pl330_resume);
> +
>  static int
>  pl330_probe(struct amba_device *adev, const struct amba_id *id)
>  {
> @@ -2738,6 +2815,12 @@ pl330_probe(struct amba_device *adev, const struct amba_id *id)
>                 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);
> +
>         return 0;
>  probe_err3:
>         /* Idle the DMAC */
> @@ -2764,6 +2847,8 @@ static int pl330_remove(struct amba_device *adev)
>         struct pl330_dmac *pl330 = amba_get_drvdata(adev);
>         struct dma_pl330_chan *pch, *_p;
>
> +       pm_runtime_get_noresume(pl330->ddma.dev);
> +
>         if (adev->dev.of_node)
>                 of_dma_controller_free(adev->dev.of_node);
>
> @@ -2802,6 +2887,7 @@ static struct amba_driver pl330_driver = {
>         .drv = {
>                 .owner = THIS_MODULE,
>                 .name = "dma-pl330",
> +               .pm = &pl330_pm,
>         },
>         .id_table = pl330_ids,
>         .probe = pl330_probe,
> --
> 1.9.1
>
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