[PATCH v2 3/4] dmaengine: switchtec-dma: add config sysfs attributes

[Logan Gunthorpe]

Add sysfs configuration options for switchtec-dma channels, using
dma_device.chan_groups the same way the ioatdma conversion does:
attach a "switchtec-config" attribute group directly to the channel's
existing struct device, with each show()/store() recovering the
struct dma_chan via the dma_chan_from_dev CLASS.

The read-modify-write of the shared perf_cfg register is protected by
hw_ctrl_lock, and writes are rejected with -EBUSY while the channel is
allocated to a client (hw_cfg_locked), instead of a TOCTOU-prone
chan->client_count check.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 drivers/dma/switchtec_dma.c | 179 ++++++++++++++++++++++++++++++++++++
 1 file changed, 179 insertions(+)

diff --git a/drivers/dma/switchtec_dma.c b/drivers/dma/switchtec_dma.c
index d73506b5cabc..d74eb48e8eca 100644
--- a/drivers/dma/switchtec_dma.c
+++ b/drivers/dma/switchtec_dma.c
@@ -132,6 +132,11 @@ struct switchtec_dma_chan {
 
 	/* Serialize hardware control register access */
 	spinlock_t hw_ctrl_lock;
+	/*
+	 * Set while the channel is allocated to a client; blocks sysfs
+	 * hw config changes
+	 */
+	bool hw_cfg_locked;
 
 	struct tasklet_struct desc_task;
 
@@ -1029,6 +1034,10 @@ static int switchtec_dma_alloc_chan_resources(struct dma_chan *chan)
 	dev_dbg(&chan->dev->device, "MRRS:        0x%x\n",
 		FIELD_GET(PERF_MRRS_MASK, perf_cfg));
 
+	spin_lock(&swdma_chan->hw_ctrl_lock);
+	swdma_chan->hw_cfg_locked = true;
+	spin_unlock(&swdma_chan->hw_ctrl_lock);
+
 	return SWITCHTEC_DMA_SQ_SIZE;
 
 err_ring_inactive:
@@ -1047,11 +1056,180 @@ static int switchtec_dma_alloc_chan_resources(struct dma_chan *chan)
 	return rc;
 }
 
+static __always_inline ssize_t perf_cfg_show(struct device *dev, char *page,
+					     unsigned int mask)
+{
+	struct switchtec_dma_chan *swdma_chan;
+	struct chan_fw_regs __iomem *chan_fw;
+	u32 perf_cfg;
+	int value;
+
+	CLASS(dma_chan_from_dev, c)(dev);
+
+	if (!c)
+		return -ENODEV;
+
+	swdma_chan = container_of(c, struct switchtec_dma_chan, dma_chan);
+	chan_fw = swdma_chan->mmio_chan_fw;
+
+	rcu_read_lock();
+	if (!rcu_dereference(swdma_chan->swdma_dev->pdev)) {
+		rcu_read_unlock();
+		return -ENODEV;
+	}
+
+	perf_cfg = readl(&chan_fw->perf_cfg);
+	value = field_get(mask, perf_cfg);
+
+	rcu_read_unlock();
+	return sysfs_emit(page, "0x%x\n", value);
+}
+
+static __always_inline ssize_t perf_cfg_store(struct device *dev,
+					      const char *page, size_t count,
+					      unsigned int mask)
+{
+	struct switchtec_dma_chan *swdma_chan;
+	struct chan_fw_regs __iomem *chan_fw;
+	ssize_t ret = count;
+	u32 perf_cfg;
+	int value;
+
+	CLASS(dma_chan_from_dev, c)(dev);
+
+	if (!c)
+		return -ENODEV;
+
+	swdma_chan = container_of(c, struct switchtec_dma_chan, dma_chan);
+	chan_fw = swdma_chan->mmio_chan_fw;
+
+	if (kstrtoint(page, 0, &value) < 0)
+		return -EINVAL;
+
+	if (value < 0 || value > field_max(mask))
+		return -EINVAL;
+
+	rcu_read_lock();
+	if (!rcu_dereference(swdma_chan->swdma_dev->pdev)) {
+		ret = -ENODEV;
+		goto err_unlock;
+	}
+
+	spin_lock(&swdma_chan->hw_ctrl_lock);
+	if (swdma_chan->hw_cfg_locked) {
+		spin_unlock(&swdma_chan->hw_ctrl_lock);
+		ret = -EBUSY;
+		goto err_unlock;
+	}
+
+	perf_cfg = readl(&chan_fw->perf_cfg);
+	perf_cfg = (perf_cfg & ~mask) | field_prep(mask, value);
+	writel(perf_cfg, &chan_fw->perf_cfg);
+	spin_unlock(&swdma_chan->hw_ctrl_lock);
+
+err_unlock:
+	rcu_read_unlock();
+	return ret;
+}
+
+static ssize_t burst_scale_show(struct device *dev,
+				struct device_attribute *attr, char *page)
+{
+	return perf_cfg_show(dev, page, PERF_BURST_SCALE_MASK);
+}
+
+static ssize_t burst_scale_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *page, size_t count)
+{
+	return perf_cfg_store(dev, page, count, PERF_BURST_SCALE_MASK);
+}
+static DEVICE_ATTR_RW(burst_scale);
+
+static ssize_t mrrs_show(struct device *dev,
+			 struct device_attribute *attr, char *page)
+{
+	return perf_cfg_show(dev, page, PERF_MRRS_MASK);
+}
+
+static ssize_t mrrs_store(struct device *dev,
+			  struct device_attribute *attr,
+			  const char *page, size_t count)
+{
+	return perf_cfg_store(dev, page, count, PERF_MRRS_MASK);
+}
+static DEVICE_ATTR_RW(mrrs);
+
+static ssize_t interval_show(struct device *dev,
+			     struct device_attribute *attr, char *page)
+{
+	return perf_cfg_show(dev, page, PERF_INTERVAL_MASK);
+}
+
+static ssize_t interval_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *page, size_t count)
+{
+	return perf_cfg_store(dev, page, count, PERF_INTERVAL_MASK);
+}
+static DEVICE_ATTR_RW(interval);
+
+static ssize_t burst_size_show(struct device *dev,
+			       struct device_attribute *attr, char *page)
+{
+	return perf_cfg_show(dev, page, PERF_BURST_SIZE_MASK);
+}
+
+static ssize_t burst_size_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *page, size_t count)
+{
+	return perf_cfg_store(dev, page, count, PERF_BURST_SIZE_MASK);
+}
+static DEVICE_ATTR_RW(burst_size);
+
+static ssize_t arb_weight_show(struct device *dev,
+			       struct device_attribute *attr, char *page)
+{
+	return perf_cfg_show(dev, page, PERF_ARB_WEIGHT_MASK);
+}
+
+static ssize_t arb_weight_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *page, size_t count)
+{
+	return perf_cfg_store(dev, page, count, PERF_ARB_WEIGHT_MASK);
+}
+static DEVICE_ATTR_RW(arb_weight);
+
+static struct attribute *switchtec_config_attrs[] = {
+	&dev_attr_burst_scale.attr,
+	&dev_attr_mrrs.attr,
+	&dev_attr_interval.attr,
+	&dev_attr_burst_size.attr,
+	&dev_attr_arb_weight.attr,
+	NULL,
+};
+
+static const struct attribute_group switchtec_config_group = {
+	.name = "switchtec-config",
+	.attrs = switchtec_config_attrs,
+};
+
+static const struct attribute_group *switchtec_groups[] = {
+	&switchtec_config_group,
+	NULL,
+};
+
 static void switchtec_dma_free_chan_resources(struct dma_chan *chan)
 {
 	struct switchtec_dma_chan *swdma_chan =
 		container_of(chan, struct switchtec_dma_chan, dma_chan);
 
+	spin_lock(&swdma_chan->hw_ctrl_lock);
+	swdma_chan->hw_cfg_locked = false;
+	spin_unlock(&swdma_chan->hw_ctrl_lock);
+
 	spin_lock_bh(&swdma_chan->submit_lock);
 	swdma_chan->ring_active = false;
 	spin_unlock_bh(&swdma_chan->submit_lock);
@@ -1318,6 +1496,7 @@ static int switchtec_dma_create(struct pci_dev *pdev)
 	dma->device_terminate_all = switchtec_dma_terminate_all;
 	dma->device_synchronize = switchtec_dma_synchronize;
 	dma->device_release = switchtec_dma_release;
+	dma->chan_groups = switchtec_groups;
 
 	rc = dma_async_device_register(dma);
 	if (rc) {
-- 
2.47.3