[PATCH 5/9] PCI: epf-mhi: Add support for DMA async read/write operation

[Manivannan Sadhasivam]

The driver currently supports only the sync read/write operation i.e., it
waits for the DMA transfer to complete before returning to the caller
(MHI stack). But it is sub-optimal and defeats the actual purpose of using
DMA.

So let's add support for DMA async read/write operation by skipping the DMA
transfer completion and returning to the caller immediately. When the
completion actually happens later, the driver will be notified using the
DMA completion handler and in turn it will notify the caller using the
newly introduced callback in "struct mhi_ep_buf_info".

Since the DMA completion handler is invoked from the interrupt context, a
separate workqueue (epf_mhi->dma_wq) is used to notify the caller about the
completion of the transfer.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
---
 drivers/pci/endpoint/functions/pci-epf-mhi.c | 231 ++++++++++++++++++-
 1 file changed, 228 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-mhi.c b/drivers/pci/endpoint/functions/pci-epf-mhi.c
index 7214f4da733b..3d09a37e5f7c 100644
--- a/drivers/pci/endpoint/functions/pci-epf-mhi.c
+++ b/drivers/pci/endpoint/functions/pci-epf-mhi.c
@@ -21,6 +21,15 @@
 /* Platform specific flags */
 #define MHI_EPF_USE_DMA BIT(0)
 
+struct pci_epf_mhi_dma_transfer {
+	struct pci_epf_mhi *epf_mhi;
+	struct mhi_ep_buf_info buf_info;
+	struct list_head node;
+	dma_addr_t paddr;
+	enum dma_data_direction dir;
+	size_t size;
+};
+
 struct pci_epf_mhi_ep_info {
 	const struct mhi_ep_cntrl_config *config;
 	struct pci_epf_header *epf_header;
@@ -124,6 +133,10 @@ struct pci_epf_mhi {
 	resource_size_t mmio_phys;
 	struct dma_chan *dma_chan_tx;
 	struct dma_chan *dma_chan_rx;
+	struct workqueue_struct *dma_wq;
+	struct work_struct dma_work;
+	struct list_head dma_list;
+	spinlock_t list_lock;
 	u32 mmio_size;
 	int irq;
 };
@@ -418,6 +431,198 @@ static int pci_epf_mhi_edma_write(struct mhi_ep_cntrl *mhi_cntrl,
 	return ret;
 }
 
+static void pci_epf_mhi_dma_worker(struct work_struct *work)
+{
+	struct pci_epf_mhi *epf_mhi = container_of(work, struct pci_epf_mhi, dma_work);
+	struct device *dma_dev = epf_mhi->epf->epc->dev.parent;
+	struct pci_epf_mhi_dma_transfer *itr, *tmp;
+	struct mhi_ep_buf_info *buf_info;
+	unsigned long flags;
+	LIST_HEAD(head);
+
+	spin_lock_irqsave(&epf_mhi->list_lock, flags);
+	list_splice_tail_init(&epf_mhi->dma_list, &head);
+	spin_unlock_irqrestore(&epf_mhi->list_lock, flags);
+
+	list_for_each_entry_safe(itr, tmp, &head, node) {
+		list_del(&itr->node);
+		dma_unmap_single(dma_dev, itr->paddr, itr->size, itr->dir);
+		buf_info = &itr->buf_info;
+		buf_info->cb(buf_info);
+		kfree(itr);
+	}
+}
+
+static void pci_epf_mhi_dma_async_callback(void *param)
+{
+	struct pci_epf_mhi_dma_transfer *transfer = param;
+	struct pci_epf_mhi *epf_mhi = transfer->epf_mhi;
+
+	spin_lock(&epf_mhi->list_lock);
+	list_add_tail(&transfer->node, &epf_mhi->dma_list);
+	spin_unlock(&epf_mhi->list_lock);
+
+	queue_work(epf_mhi->dma_wq, &epf_mhi->dma_work);
+}
+
+static int pci_epf_mhi_edma_read_async(struct mhi_ep_cntrl *mhi_cntrl,
+				       struct mhi_ep_buf_info *buf_info)
+{
+	struct pci_epf_mhi *epf_mhi = to_epf_mhi(mhi_cntrl);
+	struct device *dma_dev = epf_mhi->epf->epc->dev.parent;
+	struct pci_epf_mhi_dma_transfer *transfer = NULL;
+	struct dma_chan *chan = epf_mhi->dma_chan_rx;
+	struct device *dev = &epf_mhi->epf->dev;
+	DECLARE_COMPLETION_ONSTACK(complete);
+	struct dma_async_tx_descriptor *desc;
+	struct dma_slave_config config = {};
+	dma_cookie_t cookie;
+	dma_addr_t dst_addr;
+	int ret;
+
+	mutex_lock(&epf_mhi->lock);
+
+	config.direction = DMA_DEV_TO_MEM;
+	config.src_addr = buf_info->host_addr;
+
+	ret = dmaengine_slave_config(chan, &config);
+	if (ret) {
+		dev_err(dev, "Failed to configure DMA channel\n");
+		goto err_unlock;
+	}
+
+	dst_addr = dma_map_single(dma_dev, buf_info->dev_addr, buf_info->size,
+				  DMA_FROM_DEVICE);
+	ret = dma_mapping_error(dma_dev, dst_addr);
+	if (ret) {
+		dev_err(dev, "Failed to map remote memory\n");
+		goto err_unlock;
+	}
+
+	desc = dmaengine_prep_slave_single(chan, dst_addr, buf_info->size,
+					   DMA_DEV_TO_MEM,
+					   DMA_CTRL_ACK | DMA_PREP_INTERRUPT);
+	if (!desc) {
+		dev_err(dev, "Failed to prepare DMA\n");
+		ret = -EIO;
+		goto err_unmap;
+	}
+
+	transfer = kzalloc(sizeof(*transfer), GFP_KERNEL);
+	if (!transfer) {
+		ret = -ENOMEM;
+		goto err_unmap;
+	}
+
+	transfer->epf_mhi = epf_mhi;
+	transfer->paddr = dst_addr;
+	transfer->size = buf_info->size;
+	transfer->dir = DMA_FROM_DEVICE;
+	memcpy(&transfer->buf_info, buf_info, sizeof(*buf_info));
+
+	desc->callback = pci_epf_mhi_dma_async_callback;
+	desc->callback_param = transfer;
+
+	cookie = dmaengine_submit(desc);
+	ret = dma_submit_error(cookie);
+	if (ret) {
+		dev_err(dev, "Failed to do DMA submit\n");
+		goto err_free_transfer;
+	}
+
+	dma_async_issue_pending(chan);
+
+	goto err_unlock;
+
+err_free_transfer:
+	kfree(transfer);
+err_unmap:
+	dma_unmap_single(dma_dev, dst_addr, buf_info->size, DMA_FROM_DEVICE);
+err_unlock:
+	mutex_unlock(&epf_mhi->lock);
+
+	return ret;
+}
+
+static int pci_epf_mhi_edma_write_async(struct mhi_ep_cntrl *mhi_cntrl,
+					struct mhi_ep_buf_info *buf_info)
+{
+	struct pci_epf_mhi *epf_mhi = to_epf_mhi(mhi_cntrl);
+	struct device *dma_dev = epf_mhi->epf->epc->dev.parent;
+	struct pci_epf_mhi_dma_transfer *transfer = NULL;
+	struct dma_chan *chan = epf_mhi->dma_chan_tx;
+	struct device *dev = &epf_mhi->epf->dev;
+	DECLARE_COMPLETION_ONSTACK(complete);
+	struct dma_async_tx_descriptor *desc;
+	struct dma_slave_config config = {};
+	dma_cookie_t cookie;
+	dma_addr_t src_addr;
+	int ret;
+
+	mutex_lock(&epf_mhi->lock);
+
+	config.direction = DMA_MEM_TO_DEV;
+	config.dst_addr = buf_info->host_addr;
+
+	ret = dmaengine_slave_config(chan, &config);
+	if (ret) {
+		dev_err(dev, "Failed to configure DMA channel\n");
+		goto err_unlock;
+	}
+
+	src_addr = dma_map_single(dma_dev, buf_info->dev_addr, buf_info->size,
+				  DMA_TO_DEVICE);
+	ret = dma_mapping_error(dma_dev, src_addr);
+	if (ret) {
+		dev_err(dev, "Failed to map remote memory\n");
+		goto err_unlock;
+	}
+
+	desc = dmaengine_prep_slave_single(chan, src_addr, buf_info->size,
+					   DMA_MEM_TO_DEV,
+					   DMA_CTRL_ACK | DMA_PREP_INTERRUPT);
+	if (!desc) {
+		dev_err(dev, "Failed to prepare DMA\n");
+		ret = -EIO;
+		goto err_unmap;
+	}
+
+	transfer = kzalloc(sizeof(*transfer), GFP_KERNEL);
+	if (!transfer) {
+		ret = -ENOMEM;
+		goto err_unmap;
+	}
+
+	transfer->epf_mhi = epf_mhi;
+	transfer->paddr = src_addr;
+	transfer->size = buf_info->size;
+	transfer->dir = DMA_TO_DEVICE;
+	memcpy(&transfer->buf_info, buf_info, sizeof(*buf_info));
+
+	desc->callback = pci_epf_mhi_dma_async_callback;
+	desc->callback_param = transfer;
+
+	cookie = dmaengine_submit(desc);
+	ret = dma_submit_error(cookie);
+	if (ret) {
+		dev_err(dev, "Failed to do DMA submit\n");
+		goto err_free_transfer;
+	}
+
+	dma_async_issue_pending(chan);
+
+	goto err_unlock;
+
+err_free_transfer:
+	kfree(transfer);
+err_unmap:
+	dma_unmap_single(dma_dev, src_addr, buf_info->size, DMA_TO_DEVICE);
+err_unlock:
+	mutex_unlock(&epf_mhi->lock);
+
+	return ret;
+}
+
 struct epf_dma_filter {
 	struct device *dev;
 	u32 dma_mask;
@@ -441,6 +646,7 @@ static int pci_epf_mhi_dma_init(struct pci_epf_mhi *epf_mhi)
 	struct device *dev = &epf_mhi->epf->dev;
 	struct epf_dma_filter filter;
 	dma_cap_mask_t mask;
+	int ret;
 
 	dma_cap_zero(mask);
 	dma_cap_set(DMA_SLAVE, mask);
@@ -459,16 +665,35 @@ static int pci_epf_mhi_dma_init(struct pci_epf_mhi *epf_mhi)
 						   &filter);
 	if (IS_ERR_OR_NULL(epf_mhi->dma_chan_rx)) {
 		dev_err(dev, "Failed to request rx channel\n");
-		dma_release_channel(epf_mhi->dma_chan_tx);
-		epf_mhi->dma_chan_tx = NULL;
-		return -ENODEV;
+		ret = -ENODEV;
+		goto err_release_tx;
+	}
+
+	epf_mhi->dma_wq = alloc_workqueue("pci_epf_mhi_dma_wq", 0, 0);
+	if (!epf_mhi->dma_wq) {
+		ret = -ENOMEM;
+		goto err_release_rx;
 	}
 
+	INIT_LIST_HEAD(&epf_mhi->dma_list);
+	INIT_WORK(&epf_mhi->dma_work, pci_epf_mhi_dma_worker);
+	spin_lock_init(&epf_mhi->list_lock);
+
 	return 0;
+
+err_release_rx:
+	dma_release_channel(epf_mhi->dma_chan_rx);
+	epf_mhi->dma_chan_rx = NULL;
+err_release_tx:
+	dma_release_channel(epf_mhi->dma_chan_tx);
+	epf_mhi->dma_chan_tx = NULL;
+
+	return ret;
 }
 
 static void pci_epf_mhi_dma_deinit(struct pci_epf_mhi *epf_mhi)
 {
+	destroy_workqueue(epf_mhi->dma_wq);
 	dma_release_channel(epf_mhi->dma_chan_tx);
 	dma_release_channel(epf_mhi->dma_chan_rx);
 	epf_mhi->dma_chan_tx = NULL;
-- 
2.25.1