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Date: Thu, 25 Aug 2011 19:56:26 +0530
From: "Koul, Vinod" <vinod.koul@...el.com>
To: Guennadi Liakhovetski <g.liakhovetski@....de>
Cc: linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
Dan Williams <dan.j.williams@...el.com>,
Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH] dma: shdma: transfer based runtime PM
On Thu, 2011-08-18 at 16:55 +0200, Guennadi Liakhovetski wrote:
> Currently the shdma dmaengine driver uses runtime PM to save power, when
> no channel on the specific controller is requested by a user. This patch
> switches the driver to count individual DMA transfers. That way the
> controller can be powered down between transfers, even if some of its
> channels are in use.
No, I don't agree with the approach here, you don't need to count the
transfers, the runtime_pm framework does that very well for you.
What you need to do is to call pm_runtime_get() in your .issue_pending
callback (NOT in tx_submit anyway, this needs to be fixed in driver, see
the Documentation/dmaengine.txt
And once the transfer has completed you need to call pm_rumtime_put()
Runtime PM framework actually counts the device usage count and whenever
your device usage count goes to 0 it will call .runtime_suspend
callback, thus enable you to save power.
--
~Vinod
>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@....de>
> ---
>
> tested on mackerel (sh7372) with dmatest, sh_mobile_sdhi and sh_mmcif with
> runtime PM and STR.
>
> drivers/dma/shdma.c | 94 +++++++++++++++++++++++++++++++++++++--------------
> drivers/dma/shdma.h | 7 ++++
> 2 files changed, 75 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/dma/shdma.c b/drivers/dma/shdma.c
> index e7bb747..81809c2 100644
> --- a/drivers/dma/shdma.c
> +++ b/drivers/dma/shdma.c
> @@ -259,15 +259,23 @@ static int dmae_set_dmars(struct sh_dmae_chan *sh_chan, u16 val)
> return 0;
> }
>
> +static void sh_chan_xfer_ld_queue(struct sh_dmae_chan *sh_chan);
> +
> static dma_cookie_t sh_dmae_tx_submit(struct dma_async_tx_descriptor *tx)
> {
> struct sh_desc *desc = tx_to_sh_desc(tx), *chunk, *last = desc, *c;
> struct sh_dmae_chan *sh_chan = to_sh_chan(tx->chan);
> + struct sh_dmae_slave *param = tx->chan->private;
> dma_async_tx_callback callback = tx->callback;
> dma_cookie_t cookie;
> - unsigned long flags;
> + bool power_up;
>
> - spin_lock_irqsave(&sh_chan->desc_lock, flags);
> + spin_lock_irq(&sh_chan->desc_lock);
> +
> + if (list_empty(&sh_chan->ld_queue))
> + power_up = true;
> + else
> + power_up = false;
>
> cookie = sh_chan->common.cookie;
> cookie++;
> @@ -303,7 +311,38 @@ static dma_cookie_t sh_dmae_tx_submit(struct dma_async_tx_descriptor *tx)
> tx->cookie, &last->async_tx, sh_chan->id,
> desc->hw.sar, desc->hw.tcr, desc->hw.dar);
>
> - spin_unlock_irqrestore(&sh_chan->desc_lock, flags);
> + if (power_up) {
> + sh_chan->pm_state = DMAE_PM_BUSY;
> +
> + pm_runtime_get(sh_chan->dev);
> +
> + spin_unlock_irq(&sh_chan->desc_lock);
> +
> + pm_runtime_barrier(sh_chan->dev);
> +
> + spin_lock_irq(&sh_chan->desc_lock);
> +
> + /* Have we been reset, while waiting? */
> + if (sh_chan->pm_state != DMAE_PM_ESTABLISHED) {
> + dev_dbg(sh_chan->dev, "Bring up channel %d\n",
> + sh_chan->id);
> + if (param) {
> + const struct sh_dmae_slave_config *cfg =
> + param->config;
> +
> + dmae_set_dmars(sh_chan, cfg->mid_rid);
> + dmae_set_chcr(sh_chan, cfg->chcr);
> + } else {
> + dmae_init(sh_chan);
> + }
> +
> + if (sh_chan->pm_state == DMAE_PM_PENDING)
> + sh_chan_xfer_ld_queue(sh_chan);
> + sh_chan->pm_state = DMAE_PM_ESTABLISHED;
> + }
> + }
> +
> + spin_unlock_irq(&sh_chan->desc_lock);
>
> return cookie;
> }
> @@ -347,8 +386,6 @@ static int sh_dmae_alloc_chan_resources(struct dma_chan *chan)
> struct sh_dmae_slave *param = chan->private;
> int ret;
>
> - pm_runtime_get_sync(sh_chan->dev);
> -
> /*
> * This relies on the guarantee from dmaengine that alloc_chan_resources
> * never runs concurrently with itself or free_chan_resources.
> @@ -368,11 +405,6 @@ static int sh_dmae_alloc_chan_resources(struct dma_chan *chan)
> }
>
> param->config = cfg;
> -
> - dmae_set_dmars(sh_chan, cfg->mid_rid);
> - dmae_set_chcr(sh_chan, cfg->chcr);
> - } else {
> - dmae_init(sh_chan);
> }
>
> while (sh_chan->descs_allocated < NR_DESCS_PER_CHANNEL) {
> @@ -401,7 +433,6 @@ edescalloc:
> etestused:
> efindslave:
> chan->private = NULL;
> - pm_runtime_put(sh_chan->dev);
> return ret;
> }
>
> @@ -413,7 +444,6 @@ static void sh_dmae_free_chan_resources(struct dma_chan *chan)
> struct sh_dmae_chan *sh_chan = to_sh_chan(chan);
> struct sh_desc *desc, *_desc;
> LIST_HEAD(list);
> - int descs = sh_chan->descs_allocated;
>
> /* Protect against ISR */
> spin_lock_irq(&sh_chan->desc_lock);
> @@ -440,9 +470,6 @@ static void sh_dmae_free_chan_resources(struct dma_chan *chan)
>
> spin_unlock_irq(&sh_chan->desc_lock);
>
> - if (descs > 0)
> - pm_runtime_put(sh_chan->dev);
> -
> list_for_each_entry_safe(desc, _desc, &list, node)
> kfree(desc);
> }
> @@ -676,7 +703,6 @@ static int sh_dmae_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
> struct sh_desc, node);
> desc->partial = (desc->hw.tcr - sh_dmae_readl(sh_chan, TCR)) <<
> sh_chan->xmit_shift;
> -
> }
> spin_unlock_irqrestore(&sh_chan->desc_lock, flags);
>
> @@ -761,7 +787,13 @@ static dma_async_tx_callback __ld_cleanup(struct sh_dmae_chan *sh_chan, bool all
> async_tx_test_ack(&desc->async_tx)) || all) {
> /* Remove from ld_queue list */
> desc->mark = DESC_IDLE;
> +
> list_move(&desc->node, &sh_chan->ld_free);
> +
> + if (list_empty(&sh_chan->ld_queue)) {
> + dev_dbg(sh_chan->dev, "Bring down channel %d\n", sh_chan->id);
> + pm_runtime_put(sh_chan->dev);
> + }
> }
> }
>
> @@ -791,16 +823,14 @@ static void sh_dmae_chan_ld_cleanup(struct sh_dmae_chan *sh_chan, bool all)
> ;
> }
>
> +/* Called under spin_lock_irq(&sh_chan->desc_lock) */
> static void sh_chan_xfer_ld_queue(struct sh_dmae_chan *sh_chan)
> {
> struct sh_desc *desc;
>
> - spin_lock_irq(&sh_chan->desc_lock);
> /* DMA work check */
> - if (dmae_is_busy(sh_chan)) {
> - spin_unlock_irq(&sh_chan->desc_lock);
> + if (dmae_is_busy(sh_chan))
> return;
> - }
>
> /* Find the first not transferred descriptor */
> list_for_each_entry(desc, &sh_chan->ld_queue, node)
> @@ -813,14 +843,18 @@ static void sh_chan_xfer_ld_queue(struct sh_dmae_chan *sh_chan)
> dmae_start(sh_chan);
> break;
> }
> -
> - spin_unlock_irq(&sh_chan->desc_lock);
> }
>
> static void sh_dmae_memcpy_issue_pending(struct dma_chan *chan)
> {
> struct sh_dmae_chan *sh_chan = to_sh_chan(chan);
> - sh_chan_xfer_ld_queue(sh_chan);
> +
> + spin_lock_irq(&sh_chan->desc_lock);
> + if (sh_chan->pm_state == DMAE_PM_ESTABLISHED)
> + sh_chan_xfer_ld_queue(sh_chan);
> + else
> + sh_chan->pm_state = DMAE_PM_PENDING;
> + spin_unlock_irq(&sh_chan->desc_lock);
> }
>
> static enum dma_status sh_dmae_tx_status(struct dma_chan *chan,
> @@ -913,6 +947,12 @@ static bool sh_dmae_reset(struct sh_dmae_device *shdev)
>
> list_splice_init(&sh_chan->ld_queue, &dl);
>
> + if (!list_empty(&dl)) {
> + dev_dbg(sh_chan->dev, "Bring down channel %d\n", sh_chan->id);
> + pm_runtime_put(sh_chan->dev);
> + }
> + sh_chan->pm_state = DMAE_PM_ESTABLISHED;
> +
> spin_unlock(&sh_chan->desc_lock);
>
> /* Complete all */
> @@ -966,10 +1006,10 @@ static void dmae_do_tasklet(unsigned long data)
> break;
> }
> }
> - spin_unlock_irq(&sh_chan->desc_lock);
> -
> /* Next desc */
> sh_chan_xfer_ld_queue(sh_chan);
> + spin_unlock_irq(&sh_chan->desc_lock);
> +
> sh_dmae_chan_ld_cleanup(sh_chan, false);
> }
>
> @@ -1037,7 +1077,9 @@ static int __devinit sh_dmae_chan_probe(struct sh_dmae_device *shdev, int id,
> return -ENOMEM;
> }
>
> - /* copy struct dma_device */
> + new_sh_chan->pm_state = DMAE_PM_ESTABLISHED;
> +
> + /* reference struct dma_device */
> new_sh_chan->common.device = &shdev->common;
>
> new_sh_chan->dev = shdev->common.dev;
> diff --git a/drivers/dma/shdma.h b/drivers/dma/shdma.h
> index dc56576..2b55a27 100644
> --- a/drivers/dma/shdma.h
> +++ b/drivers/dma/shdma.h
> @@ -23,6 +23,12 @@
>
> struct device;
>
> +enum dmae_pm_state {
> + DMAE_PM_ESTABLISHED,
> + DMAE_PM_BUSY,
> + DMAE_PM_PENDING,
> +};
> +
> struct sh_dmae_chan {
> dma_cookie_t completed_cookie; /* The maximum cookie completed */
> spinlock_t desc_lock; /* Descriptor operation lock */
> @@ -38,6 +44,7 @@ struct sh_dmae_chan {
> u32 __iomem *base;
> char dev_id[16]; /* unique name per DMAC of channel */
> int pm_error;
> + enum dmae_pm_state pm_state;
> };
>
> struct sh_dmae_device {
--
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