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Date: Fri, 10 Feb 2017 10:37:40 -0600
From: Alan Tull <atull@...nel.org>
To: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
atull <atull@...nsource.altera.com>,
Moritz Fischer <moritz.fischer@...us.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-fpga@...r.kernel.org
Subject: Re: [PATCH v4 fpga 4/4] fpga zynq: Use the scatterlist interface
On Wed, Feb 1, 2017 at 1:48 PM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> wrote:
> 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@...idianresearch.com>
> Acked-by: Moritz Fischer <moritz.fischer@...us.com>
Acked-by: Alan Tull <atull@...nel.org>
> ---
> drivers/fpga/zynq-fpga.c | 174 ++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 135 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/fpga/zynq-fpga.c b/drivers/fpga/zynq-fpga.c
> index c3fc2a231e2810..34cb98139442df 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 @@ static int zynq_fpga_ops_write_init(struct fpga_manager *mgr,
> 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 @@ static int zynq_fpga_ops_write(struct fpga_manager *mgr,
> 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);
> --
> 2.7.4
>
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