Re: [PATCH v4 10/14] dmaengine: tegra-apb: Keep clock enabled only during of DMA transfer

Jon Hunter
2020-01-15T10:08:32Z

On 12/01/2020 17:30, 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 | 43 ++++++++++++++++++++++-------------
> 1 file changed, 27 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> index cc4a9ca20780..b9d8e57eaf54 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);

Is this the right place to call put? Seems that in terminate_all resume
is called after stop which will access the registers.

> }
>
> 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) {
> /*
> @@ -1280,22 +1289,15 @@ tegra_dma_prep_dma_cyclic(struct dma_chan *dc, dma_addr_t buf_addr,
> static int tegra_dma_alloc_chan_resources(struct dma_chan *dc)
> {
> struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> - struct tegra_dma *tdma = tdc->tdma;
> - int ret;
>
> dma_cookie_init(&tdc->dma_chan);
>
> - ret = pm_runtime_get_sync(tdma->dev);
> - if (ret < 0)
> - return ret;
> -
> return 0;
> }
>
> static void tegra_dma_free_chan_resources(struct dma_chan *dc)
> {
> struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> - struct tegra_dma *tdma = tdc->tdma;
> struct tegra_dma_desc *dma_desc;
> struct tegra_dma_sg_req *sg_req;
> struct list_head dma_desc_list;
> @@ -1328,7 +1330,6 @@ static void tegra_dma_free_chan_resources(struct dma_chan *dc)
> list_del(&sg_req->node);
> kfree(sg_req);
> }
> - pm_runtime_put(tdma->dev);
>
> tdc->slave_id = TEGRA_APBDMA_SLAVE_ID_INVALID;
> }
> @@ -1428,11 +1429,16 @@ static int tegra_dma_probe(struct platform_device *pdev)
>
> spin_lock_init(&tdma->global_lock);
>
> + ret = clk_prepare(tdma->dma_clk);
> + if (ret)
> + return ret;
> +
> + pm_runtime_irq_safe(&pdev->dev);
> pm_runtime_enable(&pdev->dev);
> if (!pm_runtime_enabled(&pdev->dev)) {
> ret = tegra_dma_runtime_resume(&pdev->dev);
> if (ret)
> - return ret;
> + goto err_clk_unprepare;
> } else {
> ret = pm_runtime_get_sync(&pdev->dev);

There is a get here but I don't see a put in probe.

Jon

--
nvpublic