Re: [PATCH net-next v4 4/4] net: ocelot: add FDMA support

Vladimir Oltean
2021-12-04T13:43:51Z

On Fri, Dec 03, 2021 at 06:19:16PM +0100, Clément Léger wrote:
> Ethernet frames can be extracted or injected autonomously to or from
> the device’s DDR3/DDR3L memory and/or PCIe memory space. Linked list
> data structures in memory are used for injecting or extracting Ethernet
> frames. The FDMA generates interrupts when frame extraction or
> injection is done and when the linked lists need updating.
>
> The FDMA is shared between all the ethernet ports of the switch and
> uses a linked list of descriptors (DCB) to inject and extract packets.
> Before adding descriptors, the FDMA channels must be stopped. It would
> be inefficient to do that each time a descriptor would be added so the
> channels are restarted only once they stopped.
>
> Both channels uses ring-like structure to feed the DCBs to the FDMA.
> head and tail are never touched by hardware and are completely handled
> by the driver. On top of that, page recycling has been added and is
> mostly taken from gianfar driver.
>
> Co-developed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> ---

Doesn't look too bad. Did the page reuse make any difference to the
throughput, or is the interaction with the FDMA extraction channel where
the bottleneck is?

> +static bool ocelot_fdma_add_rx_frag(struct ocelot_fdma_rx_buf *rxb, u32 stat,
> + struct sk_buff *skb, bool first)
> +{
> + int size = MSCC_FDMA_DCB_STAT_BLOCKL(stat);
> + struct page *page = rxb->page;
> +
> + if (likely(first)) {
> + skb_put(skb, size);
> + } else {
> + skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page,
> + rxb->page_offset, size, OCELOT_FDMA_RX_SIZE);
> + }
> +
> + /* Try to reuse page */
> + if (unlikely(page_count(page) != 1 || page_is_pfmemalloc(page)))

I don't think you need to go through a folio, you can use
page_ref_count() directly.

> + return false;
> +
> + /* Change offset to the other half */
> + rxb->page_offset ^= OCELOT_FDMA_RX_SIZE;
> +
> + page_ref_inc(page);
> +
> + return true;
> +}
> +
> +static void ocelot_fdma_send_skb(struct ocelot *ocelot,
> + struct ocelot_fdma *fdma, struct sk_buff *skb)
> +{
> + struct ocelot_fdma_tx_ring *tx_ring = &fdma->tx_ring;
> + struct ocelot_fdma_tx_buf *tx_buf;
> + struct ocelot_fdma_dcb *dcb;
> + dma_addr_t dma;
> + u16 next_idx;
> +
> + dcb = &tx_ring->dcbs[tx_ring->next_to_use];
> + tx_buf = &tx_ring->bufs[tx_ring->next_to_use];
> + if (!ocelot_fdma_tx_dcb_set_skb(ocelot, tx_buf, dcb, skb)) {
> + dev_kfree_skb_any(skb);
> + return;
> + }
> +
> + next_idx = ocelot_fdma_idx_next(tx_ring->next_to_use,
> + OCELOT_FDMA_TX_RING_SIZE);
> + /* If the FDMA TX chan is empty, then enqueue the DCB directly */
> + if (ocelot_fdma_tx_ring_empty(fdma)) {
> + dma = ocelot_fdma_idx_dma(tx_ring->dcbs_dma, tx_ring->next_to_use);
> + ocelot_fdma_activate_chan(fdma, dma, MSCC_FDMA_INJ_CHAN);
> + } else {
> + /* Chain the DCBs */
> + dcb->llp = ocelot_fdma_idx_dma(tx_ring->dcbs_dma, next_idx);
> + }
> +
> + tx_ring->next_to_use = next_idx;
> +
> + skb_tx_timestamp(skb);

Isn't it problematic to update tx_ring->next_to_use and skb_tx_timestamp
after you've actually called ocelot_fdma_activate_chan()? This will race
with ocelot_fdma_tx_cleanup().

> +}
> +void ocelot_fdma_init(struct platform_device *pdev, struct ocelot *ocelot)
> +{
> + struct device *dev = ocelot->dev;
> + struct ocelot_fdma *fdma;
> + void __iomem *regs;
> + int ret;
> +
> + regs = devm_platform_ioremap_resource_byname(pdev, "fdma");
> + if (IS_ERR_OR_NULL(regs))
> + return;

Shouldn't this be an optional io_target inside mscc_ocelot_probe, like
all the others are?

> +
> + fdma = devm_kzalloc(dev, sizeof(*fdma), GFP_KERNEL);
> + if (!fdma)
> + goto err_release_resource;
> +
> + ocelot->fdma = fdma;
> + ocelot->dev->coherent_dma_mask = DMA_BIT_MASK(32);
> + fdma->regs = regs;

This doesn't need to be kept inside struct ocelot_fdma, it isn't used
anywhere else.

> + fdma->regmap = regmap_init_mmio(ocelot->dev, regs,
> + &ocelot_fdma_regmap_config);
> + if (IS_ERR(fdma->regmap))
> + goto err_free_fdma;
> +
> + ocelot_fdma_writel(fdma, MSCC_FDMA_INTR_ENA, 0);
> +
> + fdma->irq = platform_get_irq_byname(pdev, "fdma");
> + ret = devm_request_irq(dev, fdma->irq, ocelot_fdma_interrupt, 0,
> + dev_name(dev), ocelot);
> + if (ret)
> + goto err_regmap_exit;
> +
> + ret = ocelot_fdma_rings_alloc(ocelot);
> + if (ret)
> + goto err_free_irq;
> +
> + static_branch_enable(&ocelot_fdma_enabled);
> +
> + return;
> +
> +err_free_irq:
> + devm_free_irq(dev, fdma->irq, fdma);
> +err_regmap_exit:
> + regmap_exit(fdma->regmap);
> +err_free_fdma:
> + devm_kfree(dev, fdma);
> +err_release_resource:
> + devm_iounmap(dev, regs);
> +
> + ocelot->fdma = NULL;
> +}
> diff --git a/drivers/net/ethernet/mscc/ocelot_vsc7514.c b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
> index 38103b0255b0..d737c680b424 100644
> --- a/drivers/net/ethernet/mscc/ocelot_vsc7514.c
> +++ b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
> @@ -18,6 +18,7 @@
>
> #include <soc/mscc/ocelot_vcap.h>
> #include <soc/mscc/ocelot_hsio.h>
> +#include "ocelot_fdma.h"
> #include "ocelot.h"
>

Please rebase all your submissions to the current net-next/master, the
following has been introduced here in the meantime, making this patch
fail to apply:

#define VSC7514_VCAP_POLICER_BASE 128
#define VSC7514_VCAP_POLICER_MAX 191

> static const u32 ocelot_ana_regmap[] = {
> @@ -1080,6 +1081,8 @@ static int mscc_ocelot_probe(struct platform_device *pdev)
> ocelot->targets[io_target[i].id] = target;
> }
>
> + ocelot_fdma_init(pdev, ocelot);
> +
> hsio = syscon_regmap_lookup_by_compatible("mscc,ocelot-hsio");
> if (IS_ERR(hsio)) {
> dev_err(&pdev->dev, "missing hsio syscon\n");
> @@ -1139,6 +1142,9 @@ static int mscc_ocelot_probe(struct platform_device *pdev)
> if (err)
> goto out_ocelot_devlink_unregister;
>
> + if (ocelot->fdma)
> + ocelot_fdma_start(ocelot);
> +
> err = ocelot_devlink_sb_register(ocelot);
> if (err)
> goto out_ocelot_release_ports;
> @@ -1179,6 +1185,8 @@ static int mscc_ocelot_remove(struct platform_device *pdev)
> {
> struct ocelot *ocelot = platform_get_drvdata(pdev);
>
> + if (ocelot->fdma)
> + ocelot_fdma_deinit(ocelot);
> devlink_unregister(ocelot->devlink);
> ocelot_deinit_timestamp(ocelot);
> ocelot_devlink_sb_unregister(ocelot);
> diff --git a/include/soc/mscc/ocelot.h b/include/soc/mscc/ocelot.h
> index 11c99fcfd341..2667a203e10f 100644
> --- a/include/soc/mscc/ocelot.h
> +++ b/include/soc/mscc/ocelot.h
> @@ -692,6 +692,12 @@ struct ocelot {
> /* Protects the PTP clock */
> spinlock_t ptp_clock_lock;
> struct ptp_pin_desc ptp_pins[OCELOT_PTP_PINS_NUM];
> +
> + struct ocelot_fdma *fdma;
> + /* Napi context used by FDMA. Needs to be in ocelot to avoid using a
> + * backpointer in ocelot_fdma
> + */
> + struct napi_struct napi;

Can it at least be dynamically allocated, and kept as a pointer here?

> };
>
> struct ocelot_policer {
> --
> 2.34.1
>