linux-kernel - Re: [PATCH 2/2] dmaengine: uniphier-xdmac: Add UniPhier external DMA controller driver

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Message-Id: <20200109211219.57FC.4A936039@socionext.com>
Date:   Thu, 09 Jan 2020 21:12:20 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH 2/2] dmaengine: uniphier-xdmac: Add UniPhier external DMA controller driver

Hi Vinod,

Thank you for your comment.

On Fri, 27 Dec 2019 12:04:11 +0530 <vkoul@...nel.org> wrote:

> On 18-12-19, 09:57, Kunihiko Hayashi wrote:
> > This adds external DMA controller driver implemented in Socionext
> > UniPhier SoCs. This driver supports DMA_MEMCPY and DMA_SLAVE modes.
> > 
> > Since this driver does not support the the way to transfer size
> > unaligned to burst width, 'src_maxburst' or 'dst_maxburst' of
> 
> You mean driver does not support any unaligned bursts?

Yes. If transfer size is unaligned to burst size, the final transfer
will be overrun.

> 
> > +static int uniphier_xdmac_probe(struct platform_device *pdev)
> > +{
> > +	struct uniphier_xdmac_device *xdev;
> > +	struct device *dev = &pdev->dev;
> > +	struct dma_device *ddev;
> > +	int irq;
> > +	int nr_chans;
> > +	int i, ret;
> > +
> > +	if (of_property_read_u32(dev->of_node, "dma-channels", &nr_chans))
> > +		return -EINVAL;
> > +	if (nr_chans > XDMAC_MAX_CHANS)
> > +		nr_chans = XDMAC_MAX_CHANS;
> > +
> > +	xdev = devm_kzalloc(dev, struct_size(xdev, channels, nr_chans),
> > +			    GFP_KERNEL);
> > +	if (!xdev)
> > +		return -ENOMEM;
> > +
> > +	xdev->nr_chans = nr_chans;
> > +	xdev->reg_base = devm_platform_ioremap_resource(pdev, 0);
> > +	if (IS_ERR(xdev->reg_base))
> > +		return PTR_ERR(xdev->reg_base);
> > +
> > +	ddev = &xdev->ddev;
> > +	ddev->dev = dev;
> > +	dma_cap_zero(ddev->cap_mask);
> > +	dma_cap_set(DMA_MEMCPY, ddev->cap_mask);
> > +	dma_cap_set(DMA_SLAVE, ddev->cap_mask);
> > +	ddev->src_addr_widths = UNIPHIER_XDMAC_BUSWIDTHS;
> > +	ddev->dst_addr_widths = UNIPHIER_XDMAC_BUSWIDTHS;
> > +	ddev->directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV) |
> > +			   BIT(DMA_MEM_TO_MEM);
> > +	ddev->residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
> > +	ddev->max_burst = XDMAC_MAX_WORDS;
> > +	ddev->device_free_chan_resources = uniphier_xdmac_free_chan_resources;
> > +	ddev->device_prep_dma_memcpy = uniphier_xdmac_prep_dma_memcpy;
> > +	ddev->device_prep_slave_sg = uniphier_xdmac_prep_slave_sg;
> > +	ddev->device_config = uniphier_xdmac_slave_config;
> > +	ddev->device_terminate_all = uniphier_xdmac_terminate_all;
> > +	ddev->device_synchronize = uniphier_xdmac_synchronize;
> > +	ddev->device_tx_status = dma_cookie_status;
> > +	ddev->device_issue_pending = uniphier_xdmac_issue_pending;
> > +	INIT_LIST_HEAD(&ddev->channels);
> > +
> > +	for (i = 0; i < nr_chans; i++) {
> > +		ret = uniphier_xdmac_chan_init(xdev, i);
> > +		if (ret) {
> > +			dev_err(dev,
> > +				"Failed to initialize XDMAC channel %d\n", i);
> > +			return ret;
> 
> so on error for channel N we leave N-1 channels initialized?

The uniphier_xdmac_chan_init() always returns 0, so this error decision
can be removed.

> > +static int uniphier_xdmac_remove(struct platform_device *pdev)
> > +{
> > +	struct uniphier_xdmac_device *xdev = platform_get_drvdata(pdev);
> > +	struct dma_device *ddev = &xdev->ddev;
> > +	struct dma_chan *chan;
> > +	int ret;
> > +
> > +	/*
> > +	 * Before reaching here, almost all descriptors have been freed by the
> > +	 * ->device_free_chan_resources() hook. However, each channel might
> > +	 * be still holding one descriptor that was on-flight at that moment.
> > +	 * Terminate it to make sure this hardware is no longer running. Then,
> > +	 * free the channel resources once again to avoid memory leak.
> > +	 */
> > +	list_for_each_entry(chan, &ddev->channels, device_node) {
> > +		ret = dmaengine_terminate_sync(chan);
> > +		if (ret)
> > +			return ret;
> > +		uniphier_xdmac_free_chan_resources(chan);
> 
> terminating sounds okayish but not freeing here. .ree_chan_resources()
> should have been called already and that should ensure that termination
> is already done...

If all transfers are complete, .device_free_chan_resources() should be called.
Since _remove() might be called asynchronously, this is post-processing just
before transfer completion.

Thank you,

---
Best Regards,
Kunihiko Hayashi