Re: [PATCH v6 11/16] dmaengine: tegra-apb: Keep clock enabled only during of DMA transfer

Jon Hunter
2020-01-30T14:09:19Z

On 30/01/2020 04:37, Dmitry Osipenko wrote:
> It's a bit impractical to enable hardware's clock at the time of DMA
> channel's allocation because most of DMA client drivers allocate DMA
> channel at the time of the driver's probing, and thus, DMA clock is kept
> always-enabled in practice, defeating the whole purpose of runtime PM.
>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
> drivers/dma/tegra20-apb-dma.c | 47 ++++++++++++++++++++++++-----------
> 1 file changed, 32 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> index 22b88ccff05d..0ee28d8e3c96 100644
> --- a/drivers/dma/tegra20-apb-dma.c
> +++ b/drivers/dma/tegra20-apb-dma.c
> @@ -436,6 +436,8 @@ static void tegra_dma_stop(struct tegra_dma_channel *tdc)
> tdc_write(tdc, TEGRA_APBDMA_CHAN_STATUS, status);
> }
> tdc->busy = false;
> +
> + pm_runtime_put(tdc->tdma->dev);
> }
>
> static void tegra_dma_start(struct tegra_dma_channel *tdc,
> @@ -500,18 +502,25 @@ static void tegra_dma_configure_for_next(struct tegra_dma_channel *tdc,
> tegra_dma_resume(tdc);
> }
>
> -static void tdc_start_head_req(struct tegra_dma_channel *tdc)
> +static bool tdc_start_head_req(struct tegra_dma_channel *tdc)
> {
> struct tegra_dma_sg_req *sg_req;
> + int err;
>
> if (list_empty(&tdc->pending_sg_req))
> - return;
> + return false;
> +
> + err = pm_runtime_get_sync(tdc->tdma->dev);
> + if (WARN_ON_ONCE(err < 0))
> + return false;
>
> sg_req = list_first_entry(&tdc->pending_sg_req, typeof(*sg_req), node);
> tegra_dma_start(tdc, sg_req);
> sg_req->configured = true;
> sg_req->words_xferred = 0;
> tdc->busy = true;
> +
> + return true;
> }
>
> static void tdc_configure_next_head_desc(struct tegra_dma_channel *tdc)
> @@ -615,6 +624,8 @@ static void handle_once_dma_done(struct tegra_dma_channel *tdc,
> }
> list_add_tail(&sgreq->node, &tdc->free_sg_req);
>
> + pm_runtime_put(tdc->tdma->dev);
> +
> /* Do not start DMA if it is going to be terminate */
> if (to_terminate || list_empty(&tdc->pending_sg_req))
> return;
> @@ -730,9 +741,7 @@ static void tegra_dma_issue_pending(struct dma_chan *dc)
> dev_err(tdc2dev(tdc), "No DMA request\n");
> goto end;
> }
> - if (!tdc->busy) {
> - tdc_start_head_req(tdc);
> -
> + if (!tdc->busy && tdc_start_head_req(tdc)) {
> /* Continuous single mode: Configure next req */
> if (tdc->cyclic) {
> /*
> @@ -775,6 +784,13 @@ static int tegra_dma_terminate_all(struct dma_chan *dc)
> else
> wcount = status;
>
> + /*
> + * tegra_dma_stop() will drop the RPM's usage refcount, but
> + * tegra_dma_resume() touches hardware and thus we should keep
> + * the DMA clock active while it's needed.
> + */
> + pm_runtime_get(tdc->tdma->dev);
> +

Would it work and make it simpler to just enable in the issue_pending
and disable in the handle_once_dma_done or terminate_all?

diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
index 3a45079d11ec..86bbb45da93d 100644
--- a/drivers/dma/tegra20-apb-dma.c
+++ b/drivers/dma/tegra20-apb-dma.c
@@ -616,9 +616,14 @@ static void handle_once_dma_done(struct
tegra_dma_channel *tdc,
list_add_tail(&sgreq->node, &tdc->free_sg_req);

/* Do not start DMA if it is going to be terminate */
- if (to_terminate || list_empty(&tdc->pending_sg_req))
+ if (to_terminate)
return;

+ if (list_empty(&tdc->pending_sg_req)) {
+ pm_runtime_put(tdc->tdma->dev);
+ return;
+ }
+
tdc_start_head_req(tdc);
}

@@ -729,6 +734,11 @@ static void tegra_dma_issue_pending(struct dma_chan
*dc)
goto end;
}
if (!tdc->busy) {
+ if (pm_runtime_get_sync(tdc->tdma->dev) < 0) {
+ dev_err(tdc2dev(tdc), "Failed to enable DMA!\n");
+ goto end;
+ }
+
tdc_start_head_req(tdc);

/* Continuous single mode: Configure next req */
@@ -788,6 +798,7 @@ static int tegra_dma_terminate_all(struct dma_chan *dc)
get_current_xferred_count(tdc, sgreq,
wcount);
}
tegra_dma_resume(tdc);
+ pm_runtime_put(tdc->tdma->dev);

skip_dma_stop:
tegra_dma_abort_all(tdc);

--
nvpublic