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

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Date:   Wed, 15 Jan 2020 10:08:25 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Vinod Koul <vkoul@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>
CC:     <dmaengine@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/14] dmaengine: tegra-apb: Keep clock enabled only
 during of DMA transfer



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@...il.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