Re: [PATCH v4 4/4] dma: pl330: add Power Management support

From: Ulf Hansson
Date: Wed Sep 17 2014 - 14:43:03 EST

On 16 September 2014 10:51, 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>
> ---
> drivers/dma/pl330.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 73 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index 4839bfa74a10..9c014874c33d 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
> @@ -1958,6 +1959,7 @@ 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 +1974,17 @@ 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 +1999,12 @@ 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 +2019,10 @@ static void pl330_tasklet(unsigned long data)
> }
> }
> spin_unlock_irqrestore(&pch->lock, flags);
> +
> + /* If work list empty, power down */
> + if (power_down)
> + pm_runtime_put(pch->dmac->ddma.dev);
> }
>
> bool pl330_filter(struct dma_chan *chan, void *param)
> @@ -2073,6 +2092,7 @@ 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 +2119,14 @@ 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_put(pl330->ddma.dev);
> break;
> case DMA_SLAVE_CONFIG:
> slave_config = (struct dma_slave_config *)arg;
> @@ -2138,6 +2162,7 @@ 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 +2172,7 @@ 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_put(pch->dmac->ddma.dev);
> }
>
> static enum dma_status
> @@ -2162,6 +2188,15 @@ 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 +2620,34 @@ 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);
> +
> + if (!pm_runtime_suspended(dev))
> + amba_pclk_disable(pcdev);

I would suggest to use pm_runtime_force_suspend() instead of the above.

> + 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);
> + if (!pm_runtime_suspended(dev))
> + return amba_pclk_enable(pcdev);

The above if statement could be replaced with pm_runtime_force_resume().

Doing that, means the amba_pclk_enable|disable() don't need to be
exported from the AMBA bus header, but entirely handled by the AMBA
bus itself.

> +
> + return 0;
> +}
> +
> +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 +2801,9 @@ 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);
>

You need pm_runtime_set_active() here as well.

> + pm_runtime_irq_safe(&adev->dev);
> + pm_runtime_put_noidle(&adev->dev);

Why pm_runtime_put_noidle(), that seems like you might end up leaving
the device in active state - unless you get some request. Likely not
what you want?

A final question, have you considered using runtime PM autosuspend
feature. Any reason to why not?

> +
> return 0;
> probe_err3:
> /* Idle the DMAC */
> @@ -2764,6 +2830,8 @@ 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 +2870,7 @@ 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
>

Kind regards
Uffe
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