Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel driver

[Vinod Koul]

On Sun, Nov 22, 2015 at 09:28:25PM -0500, Sinan Kaya wrote:
> This patch adds support for hidma engine. The driver consists
> of two logical blocks. The DMA engine interface and the
> low-level interface. The hardware only supports memcpy/memset
> and this driver only support memcpy interface. HW and driver
> doesn't support slave interface.
> 
> Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> ---
>  .../devicetree/bindings/dma/qcom_hidma.txt         |  18 +
>  drivers/dma/qcom/Kconfig                           |  10 +
>  drivers/dma/qcom/Makefile                          |   2 +
>  drivers/dma/qcom/hidma.c                           | 706 ++++++++++++++++
>  drivers/dma/qcom/hidma.h                           | 157 ++++
>  drivers/dma/qcom/hidma_dbg.c                       | 217 +++++
>  drivers/dma/qcom/hidma_ll.c                        | 924 +++++++++++++++++++++
>  7 files changed, 2034 insertions(+)

This was one of the reasons for slow review of this. I started few times but
large patches made this getting pushed back

Pls help reviewers by splitting your code which looking at this could have
been done

> +#include <linux/dmaengine.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/of_dma.h>
> +#include <linux/property.h>
> +#include <linux/delay.h>
> +#include <linux/highmem.h>
> +#include <linux/io.h>
> +#include <linux/sched.h>
> +#include <linux/wait.h>
> +#include <linux/acpi.h>
> +#include <linux/irq.h>
> +#include <linux/atomic.h>
> +#include <linux/pm_runtime.h>

Do you need so many headers...?

> +MODULE_PARM_DESC(event_channel_idx,
> +		"event channel index array for the notifications");

Can you explain this parameter in detail pls

> +static void hidma_callback(void *data)
> +{
> +	struct hidma_desc *mdesc = data;
> +	struct hidma_chan *mchan = to_hidma_chan(mdesc->desc.chan);
> +	struct dma_device *ddev = mchan->chan.device;
> +	struct hidma_dev *dmadev = to_hidma_dev(ddev);
> +	unsigned long irqflags;
> +	bool queued = false;
> +
> +	spin_lock_irqsave(&mchan->lock, irqflags);
> +	if (mdesc->node.next) {
> +		/* Delete from the active list, add to completed list */
> +		list_move_tail(&mdesc->node, &mchan->completed);
> +		queued = true;
> +	}
> +	spin_unlock_irqrestore(&mchan->lock, irqflags);
> +
> +	hidma_process_completed(dmadev);
> +
> +	if (queued) {
> +		pm_runtime_mark_last_busy(dmadev->ddev.dev);
> +		pm_runtime_put_autosuspend(dmadev->ddev.dev);
> +	}
> +}

Callback is typically referred to client callback upon dma completion, can
you explain what you are trying to do here

> +static int hidma_chan_init(struct hidma_dev *dmadev, u32 dma_sig)
> +{
> +	struct hidma_chan *mchan;
> +	struct dma_device *ddev;
> +
> +	mchan = devm_kzalloc(dmadev->ddev.dev, sizeof(*mchan), GFP_KERNEL);
> +	if (!mchan)
> +		return -ENOMEM;
> +
> +	ddev = &dmadev->ddev;
> +	mchan->dma_sig = dma_sig;
> +	mchan->dmadev = dmadev;
> +	mchan->chan.device = ddev;
> +	dma_cookie_init(&mchan->chan);
> +
> +	INIT_LIST_HEAD(&mchan->free);
> +	INIT_LIST_HEAD(&mchan->prepared);
> +	INIT_LIST_HEAD(&mchan->active);
> +	INIT_LIST_HEAD(&mchan->completed);
> +
> +	spin_lock_init(&mchan->lock);
> +	list_add_tail(&mchan->chan.device_node, &ddev->channels);
> +	dmadev->ddev.chancnt++;

Have you looked at vchan implementation and moving list handling to this
layer ?

> +	return 0;
> +}
> +
> +static void hidma_issue_pending(struct dma_chan *dmach)
> +{
> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
> +	struct hidma_dev *dmadev = mchan->dmadev;
> +
> +	/* PM will be released in hidma_callback function. */
> +	pm_runtime_get_sync(dmadev->ddev.dev);

Oh no, this is not allowed. pm_runtime_get_sync() can sleep and
issue_pending can be invoked from atomic context.

> +static enum dma_status hidma_tx_status(struct dma_chan *dmach,
> +			dma_cookie_t cookie, struct dma_tx_state *txstate)
> +{
> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
> +	enum dma_status ret;
> +
> +	if (mchan->paused)
> +		ret = DMA_PAUSED;

This is not quite right. The status query is for a descriptor and NOT for
channel. Here if the descriptor queried was running then it would be paused
for the rest pending txn, it would be DMA_IN_PROGRESS.

> +static dma_cookie_t hidma_tx_submit(struct dma_async_tx_descriptor *txd)
> +{
> +	struct hidma_chan *mchan = to_hidma_chan(txd->chan);
> +	struct hidma_dev *dmadev = mchan->dmadev;
> +	struct hidma_desc *mdesc;
> +	unsigned long irqflags;
> +	dma_cookie_t cookie;
> +
> +	if (!hidma_ll_isenabled(dmadev->lldev))
> +		return -ENODEV;

is this not too late for this check, you should fail this on prepare
method


> +static int hidma_alloc_chan_resources(struct dma_chan *dmach)
> +{
> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
> +	struct hidma_dev *dmadev = mchan->dmadev;
> +	struct hidma_desc *mdesc, *tmp;
> +	unsigned long irqflags;
> +	LIST_HEAD(descs);
> +	unsigned int i;
> +	int rc = 0;
> +
> +	if (mchan->allocated)
> +		return 0;
> +
> +	/* Alloc descriptors for this channel */
> +	for (i = 0; i < dmadev->nr_descriptors; i++) {
> +		mdesc = kzalloc(sizeof(struct hidma_desc), GFP_KERNEL);

GFP_NOWAIT pls, this can be called from atomic context

> +		if (!mdesc) {
> +			rc = -ENOMEM;
> +			break;
> +		}
> +		dma_async_tx_descriptor_init(&mdesc->desc, dmach);
> +		mdesc->desc.flags = DMA_CTRL_ACK;

what is the purpose of setting this flag here

> +static void hidma_free_chan_resources(struct dma_chan *dmach)
> +{
> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
> +	struct hidma_dev *mdma = mchan->dmadev;
> +	struct hidma_desc *mdesc, *tmp;
> +	unsigned long irqflags;
> +	LIST_HEAD(descs);
> +
> +	if (!list_empty(&mchan->prepared) || !list_empty(&mchan->active) ||
> +		!list_empty(&mchan->completed)) {
> +		/*
> +		 * We have unfinished requests waiting.
> +		 * Terminate the request from the hardware.

that sounds as bug.. free should be called when txn are completed/aborted

> +		 */
> +		hidma_cleanup_pending_tre(mdma->lldev, ERR_INFO_SW,
> +					ERR_CODE_UNEXPECTED_TERMINATE);
> +
> +		/* Give enough time for completions to be called. */
> +		msleep(100);

should we not poll/read after delay, also we are still in atomic context

> +	}
> +
> +	spin_lock_irqsave(&mchan->lock, irqflags);
> +	/* Channel must be idle */

sorry I do not like that assumption

> +	/* return all user requests */
> +	list_for_each_entry_safe(mdesc, tmp, &list, node) {
> +		struct dma_async_tx_descriptor *txd = &mdesc->desc;
> +		dma_async_tx_callback callback = mdesc->desc.callback;
> +		void *param = mdesc->desc.callback_param;
> +		enum dma_status status;
> +
> +		dma_descriptor_unmap(txd);
> +
> +		status = hidma_ll_status(dmadev->lldev, mdesc->tre_ch);
> +		/*
> +		 * The API requires that no submissions are done from a
> +		 * callback, so we don't need to drop the lock here
> +		 */

That is correct assumption for async_tx and which is deprecated now.
In fact the converse is true for rest!

> +static int hidma_pause(struct dma_chan *chan)
> +{
> +	struct hidma_chan *mchan;
> +	struct hidma_dev *dmadev;
> +
> +	mchan = to_hidma_chan(chan);
> +	dmadev = to_hidma_dev(mchan->chan.device);
> +	if (!mchan->paused) {
> +		pm_runtime_get_sync(dmadev->ddev.dev);
> +		if (hidma_ll_pause(dmadev->lldev))
> +			dev_warn(dmadev->ddev.dev, "channel did not stop\n");
> +		mchan->paused = true;
> +		pm_runtime_mark_last_busy(dmadev->ddev.dev);
> +		pm_runtime_put_autosuspend(dmadev->ddev.dev);
> +	}
> +	return 0;
> +}

This is interesting, we associate pause/resume for slave dma ops and not for
memcpy ops, what is the reason for adding pause/resume here?

> +static int hidma_remove(struct platform_device *pdev)
> +{
> +	struct hidma_dev *dmadev = platform_get_drvdata(pdev);
> +
> +	pm_runtime_get_sync(dmadev->ddev.dev);
> +	dma_async_device_unregister(&dmadev->ddev);
> +	hidma_debug_uninit(dmadev);
> +	hidma_ll_uninit(dmadev->lldev);
> +	hidma_free(dmadev);
> +
> +	dev_info(&pdev->dev, "HI-DMA engine removed\n");
> +	pm_runtime_put_sync_suspend(&pdev->dev);
> +	pm_runtime_disable(&pdev->dev);

and your irq is still active and can invoke your irq handler!

> +
> +	return 0;
> +}
> +
> +#if IS_ENABLED(CONFIG_ACPI)
> +static const struct acpi_device_id hidma_acpi_ids[] = {
> +	{"QCOM8061"},
Qcom and ACPI, that is v interesting combination !


-- 
~Vinod
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