fpga zynq: Use the scatterlist interface

This allows the driver to avoid a high order coherent DMA allocation
and memory copy. With this patch it can DMA directly from the kernel
pages that the bitfile is stored in.

Since this is now a gather DMA operation the driver uses the ISR
to feed the chips DMA queue with each entry from the SGL.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Acked-by: Moritz Fischer <moritz.fischer@ettus.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 135 insertions, 39 deletions

diff --git a/drivers/fpga/zynq-fpga.c b/drivers/fpga/zynq-fpga.c
index c3fc2a231e28..34cb98139442 100644
--- a/drivers/fpga/zynq-fpga.c
+++ b/drivers/fpga/zynq-fpga.c
@@ -30,6 +30,7 @@
 #include <linux/pm.h>
 #include <linux/regmap.h>
 #include <linux/string.h>
+#include <linux/scatterlist.h>
 
 /* Offsets into SLCR regmap */
 
@@ -80,6 +81,7 @@
 
 /* FPGA init status */
 #define STATUS_DMA_Q_F                  BIT(31)
+#define STATUS_DMA_Q_E                  BIT(30)
 #define STATUS_PCFG_INIT_MASK           BIT(4)
 
 /* Interrupt Status/Mask Register Bit definitions */
@@ -98,12 +100,16 @@
 #define DMA_INVALID_ADDRESS             GENMASK(31, 0)
 /* Used to unlock the dev */
 #define UNLOCK_MASK                     0x757bdf0d
-/* Timeout for DMA to complete */
-#define DMA_DONE_TIMEOUT                msecs_to_jiffies(1000)
 /* Timeout for polling reset bits */
 #define INIT_POLL_TIMEOUT               2500000
 /* Delay for polling reset bits */
 #define INIT_POLL_DELAY                 20
+/* Signal this is the last DMA transfer, wait for the AXI and PCAP before
+ * interrupting
+ */
+#define DMA_SRC_LAST_TRANSFER           1
+/* Timeout for DMA completion */
+#define DMA_TIMEOUT_MS                  5000
 
 /* Masks for controlling stuff in SLCR */
 /* Disable all Level shifters */
@@ -124,6 +130,11 @@ struct zynq_fpga_priv {
         void __iomem *io_base;
         struct regmap *slcr;
 
+        spinlock_t dma_lock;
+        unsigned int dma_elm;
+        unsigned int dma_nelms;
+        struct scatterlist *cur_sg;
+
         struct completion dma_done;
 };
 
@@ -149,13 +160,80 @@ static inline void zynq_fpga_set_irq(struct zynq_fpga_priv *priv, u32 enable)
         zynq_fpga_write(priv, INT_MASK_OFFSET, ~enable);
 }
 
+/* Must be called with dma_lock held */
+static void zynq_step_dma(struct zynq_fpga_priv *priv)
+{
+        u32 addr;
+        u32 len;
+        bool first;
+
+        first = priv->dma_elm == 0;
+        while (priv->cur_sg) {
+                /* Feed the DMA queue until it is full. */
+                if (zynq_fpga_read(priv, STATUS_OFFSET) & STATUS_DMA_Q_F)
+                        break;
+
+                addr = sg_dma_address(priv->cur_sg);
+                len = sg_dma_len(priv->cur_sg);
+                if (priv->dma_elm + 1 == priv->dma_nelms) {
+                        /* The last transfer waits for the PCAP to finish too,
+                         * notice this also changes the irq_mask to ignore
+                         * IXR_DMA_DONE_MASK which ensures we do not trigger
+                         * the completion too early.
+                         */
+                        addr |= DMA_SRC_LAST_TRANSFER;
+                        priv->cur_sg = NULL;
+                } else {
+                        priv->cur_sg = sg_next(priv->cur_sg);
+                        priv->dma_elm++;
+                }
+
+                zynq_fpga_write(priv, DMA_SRC_ADDR_OFFSET, addr);
+                zynq_fpga_write(priv, DMA_DST_ADDR_OFFSET, DMA_INVALID_ADDRESS);
+                zynq_fpga_write(priv, DMA_SRC_LEN_OFFSET, len / 4);
+                zynq_fpga_write(priv, DMA_DEST_LEN_OFFSET, 0);
+        }
+
+        /* Once the first transfer is queued we can turn on the ISR, future
+         * calls to zynq_step_dma will happen from the ISR context. The
+         * dma_lock spinlock guarentees this handover is done coherently, the
+         * ISR enable is put at the end to avoid another CPU spinning in the
+         * ISR on this lock.
+         */
+        if (first && priv->cur_sg) {
+                zynq_fpga_set_irq(priv,
+                                  IXR_DMA_DONE_MASK | IXR_ERROR_FLAGS_MASK);
+        } else if (!priv->cur_sg) {
+                /* The last transfer changes to DMA & PCAP mode since we do
+                 * not want to continue until everything has been flushed into
+                 * the PCAP.
+                 */
+                zynq_fpga_set_irq(priv,
+                                  IXR_D_P_DONE_MASK | IXR_ERROR_FLAGS_MASK);
+        }
+}
+
 static irqreturn_t zynq_fpga_isr(int irq, void *data)
 {
         struct zynq_fpga_priv *priv = data;
+        u32 intr_status;
 
-        /* disable DMA and error IRQs */
-        zynq_fpga_set_irq(priv, 0);
+        /* If anything other than DMA completion is reported stop and hand
+         * control back to zynq_fpga_ops_write, something went wrong,
+         * otherwise progress the DMA.
+         */
+        spin_lock(&priv->dma_lock);
+        intr_status = zynq_fpga_read(priv, INT_STS_OFFSET);
+        if (!(intr_status & IXR_ERROR_FLAGS_MASK) &&
+            (intr_status & IXR_DMA_DONE_MASK) && priv->cur_sg) {
+                zynq_fpga_write(priv, INT_STS_OFFSET, IXR_DMA_DONE_MASK);
+                zynq_step_dma(priv);
+                spin_unlock(&priv->dma_lock);
+                return IRQ_HANDLED;
+        }
+        spin_unlock(&priv->dma_lock);
 
+        zynq_fpga_set_irq(priv, 0);
         complete(&priv->dma_done);
 
         return IRQ_HANDLED;
@@ -266,10 +344,11 @@ static int zynq_fpga_ops_write_init(struct fpga_manager *mgr,
         zynq_fpga_write(priv, CTRL_OFFSET,
                         (CTRL_PCAP_PR_MASK | CTRL_PCAP_MODE_MASK | ctrl));
 
-        /* check that we have room in the command queue */
+        /* We expect that the command queue is empty right now. */
         status = zynq_fpga_read(priv, STATUS_OFFSET);
-        if (status & STATUS_DMA_Q_F) {
-                dev_err(&mgr->dev, "DMA command queue full\n");
+        if ((status & STATUS_DMA_Q_F) ||
+            (status & STATUS_DMA_Q_E) != STATUS_DMA_Q_E) {
+                dev_err(&mgr->dev, "DMA command queue not right\n");
                 err = -EBUSY;
                 goto out_err;
         }
@@ -288,27 +367,36 @@ out_err:
         return err;
 }
 
-static int zynq_fpga_ops_write(struct fpga_manager *mgr,
-                               const char *buf, size_t count)
+static int zynq_fpga_ops_write(struct fpga_manager *mgr, struct sg_table *sgt)
 {
         struct zynq_fpga_priv *priv;
         const char *why;
         int err;
-        char *kbuf;
-        size_t in_count;
-        dma_addr_t dma_addr;
-        u32 transfer_length;
         u32 intr_status;
+        unsigned long timeout;
+        unsigned long flags;
+        struct scatterlist *sg;
+        int i;
 
-        in_count = count;
         priv = mgr->priv;
 
-        kbuf =
-            dma_alloc_coherent(mgr->dev.parent, count, &dma_addr, GFP_KERNEL);
-        if (!kbuf)
-                return -ENOMEM;
+        /* The hardware can only DMA multiples of 4 bytes, and it requires the
+         * starting addresses to be aligned to 64 bits (UG585 pg 212).
+         */
+        for_each_sg(sgt->sgl, sg, sgt->nents, i) {
+                if ((sg->offset % 8) || (sg->length % 4)) {
+                        dev_err(&mgr->dev,
+                            "Invalid bitstream, chunks must be aligned\n");
+                        return -EINVAL;
+                }
+        }
 
-        memcpy(kbuf, buf, count);
+        priv->dma_nelms =
+            dma_map_sg(mgr->dev.parent, sgt->sgl, sgt->nents, DMA_TO_DEVICE);
+        if (priv->dma_nelms == 0) {
+                dev_err(&mgr->dev, "Unable to DMA map (TO_DEVICE)\n");
+                return -ENOMEM;
+        }
 
         /* enable clock */
         err = clk_enable(priv->clk);
@@ -316,28 +404,31 @@ static int zynq_fpga_ops_write(struct fpga_manager *mgr,
                 goto out_free;
 
         zynq_fpga_write(priv, INT_STS_OFFSET, IXR_ALL_MASK);
-
         reinit_completion(&priv->dma_done);
 
-        /* enable DMA and error IRQs */
-        zynq_fpga_set_irq(priv, IXR_D_P_DONE_MASK | IXR_ERROR_FLAGS_MASK);
-
-        /* the +1 in the src addr is used to hold off on DMA_DONE IRQ
-         * until both AXI and PCAP are done ...
-         */
-        zynq_fpga_write(priv, DMA_SRC_ADDR_OFFSET, (u32)(dma_addr) + 1);
-        zynq_fpga_write(priv, DMA_DST_ADDR_OFFSET, (u32)DMA_INVALID_ADDRESS);
-
-        /* convert #bytes to #words */
-        transfer_length = (count + 3) / 4;
+        /* zynq_step_dma will turn on interrupts */
+        spin_lock_irqsave(&priv->dma_lock, flags);
+        priv->dma_elm = 0;
+        priv->cur_sg = sgt->sgl;
+        zynq_step_dma(priv);
+        spin_unlock_irqrestore(&priv->dma_lock, flags);
 
-        zynq_fpga_write(priv, DMA_SRC_LEN_OFFSET, transfer_length);
-        zynq_fpga_write(priv, DMA_DEST_LEN_OFFSET, 0);
+        timeout = wait_for_completion_timeout(&priv->dma_done,
+                                              msecs_to_jiffies(DMA_TIMEOUT_MS));
 
-        wait_for_completion(&priv->dma_done);
+        spin_lock_irqsave(&priv->dma_lock, flags);
+        zynq_fpga_set_irq(priv, 0);
+        priv->cur_sg = NULL;
+        spin_unlock_irqrestore(&priv->dma_lock, flags);
 
         intr_status = zynq_fpga_read(priv, INT_STS_OFFSET);
-        zynq_fpga_write(priv, INT_STS_OFFSET, intr_status);
+        zynq_fpga_write(priv, INT_STS_OFFSET, IXR_ALL_MASK);
+
+        /* There doesn't seem to be a way to force cancel any DMA, so if
+         * something went wrong we are relying on the hardware to have halted
+         * the DMA before we get here, if there was we could use
+         * wait_for_completion_interruptible too.
+         */
 
         if (intr_status & IXR_ERROR_FLAGS_MASK) {
                 why = "DMA reported error";
@@ -345,8 +436,12 @@ static int zynq_fpga_ops_write(struct fpga_manager *mgr,
                 goto out_report;
         }
 
-        if (!((intr_status & IXR_D_P_DONE_MASK) == IXR_D_P_DONE_MASK)) {
-                why = "DMA did not complete";
+        if (priv->cur_sg ||
+            !((intr_status & IXR_D_P_DONE_MASK) == IXR_D_P_DONE_MASK)) {
+                if (timeout == 0)
+                        why = "DMA timed out";
+                else
+                        why = "DMA did not complete";
                 err = -EIO;
                 goto out_report;
         }
@@ -369,7 +464,7 @@ out_clk:
         clk_disable(priv->clk);
 
 out_free:
-        dma_free_coherent(mgr->dev.parent, count, kbuf, dma_addr);
+        dma_unmap_sg(mgr->dev.parent, sgt->sgl, sgt->nents, DMA_TO_DEVICE);
         return err;
 }
 
@@ -433,7 +528,7 @@ static const struct fpga_manager_ops zynq_fpga_ops = {
         .initial_header_size = 128,
         .state = zynq_fpga_ops_state,
         .write_init = zynq_fpga_ops_write_init,
-        .write = zynq_fpga_ops_write,
+        .write_sg = zynq_fpga_ops_write,
         .write_complete = zynq_fpga_ops_write_complete,
 };
 
@@ -447,6 +542,7 @@ static int zynq_fpga_probe(struct platform_device *pdev)
         priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
         if (!priv)
                 return -ENOMEM;
+        spin_lock_init(&priv->dma_lock);
 
         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
         priv->io_base = devm_ioremap_resource(dev, res);