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Subject: Re: [PATCH v2 5/6] net: ocelot: add FDMA support
To:     =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= <clement.leger@bootlin.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Vladimir Oltean <vladimir.oltean@nxp.com>,
        Claudiu Manoil <claudiu.manoil@nxp.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        UNGLinuxDriver@microchip.com, Andrew Lunn <andrew@lunn.ch>
Cc:     netdev@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>
References: <20211103091943.3878621-1-clement.leger@bootlin.com>
 <20211103091943.3878621-6-clement.leger@bootlin.com>
From:   Denis Kirjanov <dkirjanov@suse.de>
Message-ID: <d52f87ea-e6b6-34b4-d6cc-ec179ae3486c@suse.de>
Date:   Wed, 3 Nov 2021 14:25:46 +0300
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11/3/21 12:19 PM, Clément Léger пишет:
> 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,
> 
> TX path uses multiple lists to handle descriptors. tx_ongoing is the list
> of DCB currently owned by the hardware, tx_queued is a list of DCB that
> will be given to the hardware when tx_ongoing is done and finally
> tx_free_dcb is the list of DCB available for TX.
> 
> RX path uses two list, rx_hw is the list of DCB currently given to the
> hardware and rx_sw is the list of descriptors that have been completed
> by the FDMA and will be reinjected when the DMA hits the end of the
> linked list.
> 
> 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>
> ---
>   drivers/net/ethernet/mscc/Makefile         |   1 +
>   drivers/net/ethernet/mscc/ocelot.h         |   1 +
>   drivers/net/ethernet/mscc/ocelot_fdma.c    | 693 +++++++++++++++++++++
>   drivers/net/ethernet/mscc/ocelot_fdma.h    |  59 ++
>   drivers/net/ethernet/mscc/ocelot_net.c     |  11 +-
>   drivers/net/ethernet/mscc/ocelot_vsc7514.c |  15 +
>   include/soc/mscc/ocelot.h                  |   2 +
>   7 files changed, 779 insertions(+), 3 deletions(-)
>   create mode 100644 drivers/net/ethernet/mscc/ocelot_fdma.c
>   create mode 100644 drivers/net/ethernet/mscc/ocelot_fdma.h
> 
> diff --git a/drivers/net/ethernet/mscc/Makefile b/drivers/net/ethernet/mscc/Makefile
> index 722c27694b21..d76a9b78b6ca 100644
> --- a/drivers/net/ethernet/mscc/Makefile
> +++ b/drivers/net/ethernet/mscc/Makefile
> @@ -11,5 +11,6 @@ mscc_ocelot_switch_lib-y := \
>   mscc_ocelot_switch_lib-$(CONFIG_BRIDGE_MRP) += ocelot_mrp.o
>   obj-$(CONFIG_MSCC_OCELOT_SWITCH) += mscc_ocelot.o
>   mscc_ocelot-y := \
> +	ocelot_fdma.o \
>   	ocelot_vsc7514.o \
>   	ocelot_net.o
> diff --git a/drivers/net/ethernet/mscc/ocelot.h b/drivers/net/ethernet/mscc/ocelot.h
> index ba0dec7dd64f..ad85ad1079ad 100644
> --- a/drivers/net/ethernet/mscc/ocelot.h
> +++ b/drivers/net/ethernet/mscc/ocelot.h
> @@ -9,6 +9,7 @@
>   #define _MSCC_OCELOT_H_
>   
>   #include <linux/bitops.h>
> +#include <linux/dsa/ocelot.h>
>   #include <linux/etherdevice.h>
>   #include <linux/if_vlan.h>
>   #include <linux/net_tstamp.h>
> diff --git a/drivers/net/ethernet/mscc/ocelot_fdma.c b/drivers/net/ethernet/mscc/ocelot_fdma.c
> new file mode 100644
> index 000000000000..d8cdf022bbee
> --- /dev/null
> +++ b/drivers/net/ethernet/mscc/ocelot_fdma.c
> @@ -0,0 +1,693 @@
> +// SPDX-License-Identifier: (GPL-2.0 OR MIT)
> +/*
> + * Microsemi SoCs FDMA driver
> + *
> + * Copyright (c) 2021 Microchip
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/dmapool.h>
> +#include <linux/dsa/ocelot.h>
> +#include <linux/netdevice.h>
> +#include <linux/of_platform.h>
> +#include <linux/skbuff.h>
> +
> +#include "ocelot_fdma.h"
> +#include "ocelot_qs.h"
> +
> +#define MSCC_FDMA_DCB_LLP(x)			((x) * 4 + 0x0)
> +
> +#define MSCC_FDMA_DCB_STAT_BLOCKO(x)		(((x) << 20) & GENMASK(31, 20))
> +#define MSCC_FDMA_DCB_STAT_BLOCKO_M		GENMASK(31, 20)
> +#define MSCC_FDMA_DCB_STAT_BLOCKO_X(x)		(((x) & GENMASK(31, 20)) >> 20)
> +#define MSCC_FDMA_DCB_STAT_PD			BIT(19)
> +#define MSCC_FDMA_DCB_STAT_ABORT		BIT(18)
> +#define MSCC_FDMA_DCB_STAT_EOF			BIT(17)
> +#define MSCC_FDMA_DCB_STAT_SOF			BIT(16)
> +#define MSCC_FDMA_DCB_STAT_BLOCKL_M		GENMASK(15, 0)
> +#define MSCC_FDMA_DCB_STAT_BLOCKL(x)		((x) & GENMASK(15, 0))
> +
> +#define MSCC_FDMA_CH_SAFE			0xcc
> +
> +#define MSCC_FDMA_CH_ACTIVATE			0xd0
> +
> +#define MSCC_FDMA_CH_DISABLE			0xd4
> +
> +#define MSCC_FDMA_EVT_ERR			0x164
> +
> +#define MSCC_FDMA_EVT_ERR_CODE			0x168
> +
> +#define MSCC_FDMA_INTR_LLP			0x16c
> +
> +#define MSCC_FDMA_INTR_LLP_ENA			0x170
> +
> +#define MSCC_FDMA_INTR_FRM			0x174
> +
> +#define MSCC_FDMA_INTR_FRM_ENA			0x178
> +
> +#define MSCC_FDMA_INTR_ENA			0x184
> +
> +#define MSCC_FDMA_INTR_IDENT			0x188
> +
> +#define MSCC_FDMA_INJ_CHAN			2
> +#define MSCC_FDMA_XTR_CHAN			0
> +
> +#define FDMA_MAX_SKB				256
> +#define FDMA_WEIGHT				32
> +
> +#define OCELOT_TAG_WORD_LEN			(OCELOT_TAG_LEN / 4)
> +
> +/* Add 4 for possible misalignment when mapping the data */
> +#define FDMA_RX_EXTRA_SIZE			\
> +	(OCELOT_TAG_LEN + ETH_FCS_LEN + ETH_HLEN + 4)
> +
> +struct ocelot_fdma_dcb_hw_v2 {
> +	u32 llp;
> +	u32 datap;
> +	u32 datal;
> +	u32 stat;
> +};
> +
> +struct ocelot_fdma_dcb {
> +	struct ocelot_fdma_dcb_hw_v2	hw;
> +	struct list_head		node;
> +	struct sk_buff			*skb;
> +	dma_addr_t			mapping;
> +	size_t				mapped_size;
> +	dma_addr_t			phys;
> +};
> +
> +static int fdma_rx_compute_buffer_size(int mtu)
> +{
> +	return ALIGN(mtu + FDMA_RX_EXTRA_SIZE, 4);
> +}
> +
> +static void fdma_writel(struct ocelot_fdma *fdma, u32 reg, u32 data)
> +{
> +	writel(data, fdma->base + reg);
> +}
> +
> +static u32 fdma_readl(struct ocelot_fdma *fdma, u32 reg)
> +{
> +	return readl(fdma->base + reg);
> +}
> +
> +static void fdma_activate_chan(struct ocelot_fdma *fdma,
> +			       struct ocelot_fdma_dcb *dcb, int chan)
> +{
> +	fdma_writel(fdma, MSCC_FDMA_DCB_LLP(chan), dcb->phys);
> +	fdma_writel(fdma, MSCC_FDMA_CH_ACTIVATE, BIT(chan));
> +}
> +
> +static void fdma_stop_channel(struct ocelot_fdma *fdma, int chan)
> +{
> +	u32 safe;
> +
> +	fdma_writel(fdma, MSCC_FDMA_CH_DISABLE, BIT(chan));
> +	do {
> +		safe = fdma_readl(fdma, MSCC_FDMA_CH_SAFE);
> +	} while (!(safe & BIT(chan)));
timeout?

> +}
> +
> +static bool ocelot_fdma_dcb_set_data(struct ocelot_fdma *fdma,
> +				     struct ocelot_fdma_dcb *dcb, void *data,
> +				     size_t size, enum dma_data_direction dir)
> +{
> +	u32 offset;
> +
> +	dcb->mapped_size = size;
> +	dcb->mapping = dma_map_single(fdma->dev, data, size, dir);
> +	if (unlikely(dma_mapping_error(fdma->dev, dcb->mapping)))
> +		return false;
> +
> +	offset = dcb->mapping & 0x3;
> +
> +	dcb->hw.llp = 0;
> +	dcb->hw.datap = dcb->mapping & ~0x3;
> +	/* DATAL must be a multiple of word size */
> +	dcb->hw.datal = ALIGN_DOWN(size - offset, 4);
> +	dcb->hw.stat = MSCC_FDMA_DCB_STAT_BLOCKO(offset);
> +
> +	return true;
> +}
> +
> +static bool ocelot_fdma_dcb_set_rx_skb(struct ocelot_fdma *fdma,
> +				       struct ocelot_fdma_dcb *dcb,
> +				       struct sk_buff *skb, size_t size)
> +{
> +	dcb->skb = skb;
> +	return ocelot_fdma_dcb_set_data(fdma, dcb, skb->data, size,
> +				      DMA_FROM_DEVICE);
> +}
> +
> +static bool ocelot_fdma_dcb_set_tx_skb(struct ocelot_fdma *fdma,
> +				       struct ocelot_fdma_dcb *dcb,
> +				       struct sk_buff *skb)
> +{
> +	if (!ocelot_fdma_dcb_set_data(fdma, dcb, skb->data, skb->len,
> +				      DMA_TO_DEVICE))
> +		return false;
> +
> +	dcb->skb = skb;
> +	dcb->hw.stat |= MSCC_FDMA_DCB_STAT_BLOCKL(skb->len);
> +	dcb->hw.stat |= MSCC_FDMA_DCB_STAT_SOF | MSCC_FDMA_DCB_STAT_EOF;
> +
> +	return true;
> +}
> +
> +static struct ocelot_fdma_dcb *fdma_dcb_alloc(struct ocelot_fdma *fdma)
> +{
> +	struct ocelot_fdma_dcb *dcb;
> +	dma_addr_t phys;
> +
> +	dcb = dma_pool_zalloc(fdma->dcb_pool, GFP_KERNEL, &phys);
> +	if (unlikely(!dcb))
> +		return NULL;
> +
> +	dcb->phys = phys;
> +
> +	return dcb;
> +}
> +
> +static struct net_device *fdma_get_port_netdev(struct ocelot_fdma *fdma,
> +					       int port_num)
> +{
> +	struct ocelot_port_private *port_priv;
> +	struct ocelot *ocelot = fdma->ocelot;
> +	struct ocelot_port *port;
> +
> +	if (port_num >= ocelot->num_phys_ports)
> +		return NULL;
> +
> +	port = ocelot->ports[port_num];
> +
> +	if (!port)
> +		return NULL;
> +
> +	port_priv = container_of(port, struct ocelot_port_private, port);
> +
> +	return port_priv->dev;
> +}
> +
> +static bool ocelot_fdma_rx_process_skb(struct ocelot_fdma *fdma,
> +				       struct ocelot_fdma_dcb *dcb,
> +				       int budget)
> +{
> +	struct sk_buff *skb = dcb->skb;
> +	struct net_device *ndev;
> +	u64 src_port;
> +	void *xfh;
> +
> +	dma_unmap_single(fdma->dev, dcb->mapping, dcb->mapped_size,
> +			 DMA_FROM_DEVICE);
> +
> +	xfh = skb->data;
> +	ocelot_xfh_get_src_port(xfh, &src_port);
> +
> +	skb_put(skb, MSCC_FDMA_DCB_STAT_BLOCKL(dcb->hw.stat));
> +	skb_pull(skb, OCELOT_TAG_LEN);
> +
> +	ndev = fdma_get_port_netdev(fdma, src_port);
> +	if (unlikely(!ndev)) {
> +		napi_consume_skb(dcb->skb, budget);
> +		return false;
> +	}
> +
> +	skb->dev = ndev;
> +	skb->protocol = eth_type_trans(skb, skb->dev);
> +	skb->dev->stats.rx_bytes += skb->len;
> +	skb->dev->stats.rx_packets++;
> +
> +	netif_receive_skb(skb);
> +
> +	return true;
> +}
> +
> +static void ocelot_fdma_rx_refill(struct ocelot_fdma *fdma)
> +{
> +	struct ocelot_fdma_dcb *dcb, *last_dcb;
> +
> +	WARN_ON(list_empty(&fdma->rx_sw));
> +
> +	dcb = list_first_entry(&fdma->rx_sw, struct ocelot_fdma_dcb, node);
> +	/* Splice old hardware DCB list + new one */
> +	if (!list_empty(&fdma->rx_hw)) {
> +		last_dcb = list_last_entry(&fdma->rx_hw, struct ocelot_fdma_dcb,
> +					   node);
> +		last_dcb->hw.llp = dcb->phys;
> +	}
> +
> +	/* Move software list to hardware list */
> +	list_splice_tail_init(&fdma->rx_sw, &fdma->rx_hw);
> +
> +	/* Finally reactivate the channel */
> +	fdma_activate_chan(fdma, dcb, MSCC_FDMA_XTR_CHAN);
> +}
> +
> +static void ocelot_fdma_list_add_dcb(struct list_head *list,
> +				     struct ocelot_fdma_dcb *dcb)
> +{
> +	struct ocelot_fdma_dcb *last_dcb;
> +
> +	if (!list_empty(list)) {
> +		last_dcb = list_last_entry(list, struct ocelot_fdma_dcb, node);
> +		last_dcb->hw.llp = dcb->phys;
> +	}
> +
> +	list_add_tail(&dcb->node, list);
> +}
> +
> +static bool ocelot_fdma_rx_add_dcb_sw(struct ocelot_fdma *fdma,
> +				      struct ocelot_fdma_dcb *dcb)
> +{
> +	struct sk_buff *new_skb;
> +
> +	/* Add DCB to end of list with new SKB */
> +	new_skb = napi_alloc_skb(&fdma->napi, fdma->rx_buf_size);
> +	if (unlikely(!new_skb)) {
> +		pr_err("skb_alloc failed\n");
> +		return false;
> +	}
> +
> +	ocelot_fdma_dcb_set_rx_skb(fdma, dcb, new_skb, fdma->rx_buf_size);
> +	ocelot_fdma_list_add_dcb(&fdma->rx_sw, dcb);
> +
> +	return true;
> +}
> +
> +static bool ocelot_fdma_rx_get(struct ocelot_fdma *fdma, int budget)
> +{
> +	struct ocelot_fdma_dcb *dcb;
> +	bool valid = true;
> +	u32 stat;
> +
> +	dcb = list_first_entry_or_null(&fdma->rx_hw, struct ocelot_fdma_dcb,
> +				       node);
> +	if (!dcb || MSCC_FDMA_DCB_STAT_BLOCKL(dcb->hw.stat) == 0)
> +		return false;
> +
> +	list_del(&dcb->node);
> +
> +	stat = dcb->hw.stat;
> +	if (stat & MSCC_FDMA_DCB_STAT_ABORT || stat & MSCC_FDMA_DCB_STAT_PD)
> +		valid = false;
> +
> +	if (!(stat & MSCC_FDMA_DCB_STAT_SOF) ||
> +	    !(stat & MSCC_FDMA_DCB_STAT_EOF))
> +		valid = false;
> +
> +	if (likely(valid)) {
> +		if (!ocelot_fdma_rx_process_skb(fdma, dcb, budget))
> +			pr_err("Process skb failed, stat %x\n", stat);
> +	} else {
> +		napi_consume_skb(dcb->skb, budget);
> +	}
> +
> +	return ocelot_fdma_rx_add_dcb_sw(fdma, dcb);
> +}
> +
> +static void ocelot_fdma_rx_check_stopped(struct ocelot_fdma *fdma)
> +{
> +	u32 llp = fdma_readl(fdma, MSCC_FDMA_DCB_LLP(MSCC_FDMA_XTR_CHAN));
> +	/* LLP is non NULL, FDMA is still fetching packets */
> +	if (llp)
> +		return;
> +
> +	fdma_stop_channel(fdma, MSCC_FDMA_XTR_CHAN);
> +	ocelot_fdma_rx_refill(fdma);
> +}
> +
> +static void ocelot_fdma_tx_free_dcb(struct ocelot_fdma *fdma,
> +				    struct list_head *list)
> +{
> +	struct ocelot_fdma_dcb *dcb;
> +
> +	if (list_empty(list))
> +		return;
> +
> +	/* Free all SKBs that have been used for TX */
> +	list_for_each_entry(dcb, list, node) {
> +		dma_unmap_single(fdma->dev, dcb->mapping, dcb->mapped_size,
> +				 DMA_TO_DEVICE);
> +		dev_consume_skb_any(dcb->skb);
> +		dcb->skb = NULL;
> +	}
> +
> +	/* All DCBs can now be given to free list */
> +	spin_lock(&fdma->tx_free_lock);
> +	list_splice_tail_init(list, &fdma->tx_free_dcb);
> +	spin_unlock(&fdma->tx_free_lock);
> +}
> +
> +static void ocelot_fdma_tx_cleanup(struct ocelot_fdma *fdma)
> +{
> +	struct list_head tx_done = LIST_HEAD_INIT(tx_done);
> +	struct ocelot_fdma_dcb *dcb, *temp;
> +
> +	spin_lock(&fdma->tx_enqueue_lock);
> +	if (list_empty(&fdma->tx_ongoing))
> +		goto out_unlock;
> +
> +	list_for_each_entry_safe(dcb, temp, &fdma->tx_ongoing, node) {
> +		if (!(dcb->hw.stat & MSCC_FDMA_DCB_STAT_PD))
> +			break;
> +
> +		list_move_tail(&dcb->node, &tx_done);
> +	}
> +
> +out_unlock:
> +	spin_unlock(&fdma->tx_enqueue_lock);
> +
> +	ocelot_fdma_tx_free_dcb(fdma, &tx_done);
> +}
> +
> +static void ocelot_fdma_tx_restart(struct ocelot_fdma *fdma)
> +{
> +	struct ocelot_fdma_dcb *dcb;
> +	u32 safe;
> +
> +	spin_lock(&fdma->tx_enqueue_lock);
> +
> +	if (!list_empty(&fdma->tx_ongoing) || list_empty(&fdma->tx_queued))
> +		goto out_unlock;
> +
> +	/* Ongoing list is empty, channel should be in safe mode */
> +	do {
> +		safe = fdma_readl(fdma, MSCC_FDMA_CH_SAFE);
> +	} while (!(safe & BIT(MSCC_FDMA_INJ_CHAN)));
timeout?
> +
> +	/* Move queued DCB to ongoing and restart the DMA */
> +	list_splice_tail_init(&fdma->tx_queued, &fdma->tx_ongoing);
> +	/* List can't be empty, no need to check */
> +	dcb = list_first_entry(&fdma->tx_ongoing, struct ocelot_fdma_dcb, node);
> +
> +	fdma_activate_chan(fdma, dcb, MSCC_FDMA_INJ_CHAN);
> +
> +out_unlock:
> +	spin_unlock(&fdma->tx_enqueue_lock);
> +}
> +
> +static int ocelot_fdma_napi_poll(struct napi_struct *napi, int budget)
> +{
> +	struct ocelot_fdma *fdma = container_of(napi, struct ocelot_fdma, napi);
> +	int work_done = 0;
> +
> +	ocelot_fdma_tx_cleanup(fdma);
> +	ocelot_fdma_tx_restart(fdma);
> +
> +	while (work_done < budget) {
> +		if (!ocelot_fdma_rx_get(fdma, budget))
> +			break;
> +
> +		work_done++;
> +	}
> +
> +	ocelot_fdma_rx_check_stopped(fdma);
> +
> +	if (work_done < budget) {
> +		napi_complete(&fdma->napi);
> +		fdma_writel(fdma, MSCC_FDMA_INTR_ENA,
> +			    BIT(MSCC_FDMA_INJ_CHAN) | BIT(MSCC_FDMA_XTR_CHAN));
> +	}
> +
> +	return work_done;
> +}
> +
> +static irqreturn_t ocelot_fdma_interrupt(int irq, void *dev_id)
> +{
> +	u32 ident, llp, frm, err, err_code;
> +	struct ocelot_fdma *fdma = dev_id;
> +
> +	ident = fdma_readl(fdma, MSCC_FDMA_INTR_IDENT);
> +	frm = fdma_readl(fdma, MSCC_FDMA_INTR_FRM);
> +	llp = fdma_readl(fdma, MSCC_FDMA_INTR_LLP);
> +
> +	fdma_writel(fdma, MSCC_FDMA_INTR_LLP, llp & ident);
> +	fdma_writel(fdma, MSCC_FDMA_INTR_FRM, frm & ident);
> +	if (frm | llp) {
> +		fdma_writel(fdma, MSCC_FDMA_INTR_ENA, 0);
> +		napi_schedule(&fdma->napi);
> +	}
> +
> +	err = fdma_readl(fdma, MSCC_FDMA_EVT_ERR);
> +	if (unlikely(err)) {
> +		err_code = fdma_readl(fdma, MSCC_FDMA_EVT_ERR_CODE);
> +		dev_err_ratelimited(fdma->dev,
> +				    "Error ! chans mask: %#x, code: %#x\n",
> +				    err, err_code);
> +
> +		fdma_writel(fdma, MSCC_FDMA_EVT_ERR, err);
> +		fdma_writel(fdma, MSCC_FDMA_EVT_ERR_CODE, err_code);
> +	}
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static struct ocelot_fdma_dcb *fdma_tx_get_dcb(struct ocelot_fdma *fdma)
> +{
> +	struct ocelot_fdma_dcb *dcb = NULL;
> +
> +	spin_lock_bh(&fdma->tx_free_lock);
> +	dcb = list_first_entry_or_null(&fdma->tx_free_dcb,
> +				       struct ocelot_fdma_dcb, node);
> +	if (dcb)
> +		list_del(&dcb->node);
> +
> +	spin_unlock_bh(&fdma->tx_free_lock);
> +
> +	return dcb;
> +}
> +
> +int ocelot_fdma_inject_frame(struct ocelot_fdma *fdma, int port, u32 rew_op,
> +			     struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct ocelot_port *port_s = fdma->ocelot->ports[port];
> +	struct ocelot_fdma_dcb *dcb;
> +	struct sk_buff *new_skb;
> +	void *ifh;
> +
> +	if (unlikely(skb_shinfo(skb)->nr_frags != 0)) {
> +		netdev_err(dev, "Unsupported fragmented packet");
> +		dev_kfree_skb_any(skb);
> +		return NETDEV_TX_OK;
> +	}
> +
> +	if (skb_headroom(skb) < OCELOT_TAG_LEN ||
> +	    skb_tailroom(skb) < ETH_FCS_LEN) {
> +		new_skb = skb_copy_expand(skb, OCELOT_TAG_LEN, ETH_FCS_LEN,
> +					  GFP_ATOMIC);
> +		dev_consume_skb_any(skb);
> +		if (!new_skb)
> +			return NETDEV_TX_OK;
> +
> +		skb = new_skb;
> +	}
> +
> +	ifh = skb_push(skb, OCELOT_TAG_LEN);
> +	skb_put(skb, ETH_FCS_LEN);
> +	ocelot_ifh_port_set(ifh, port_s, rew_op, skb_vlan_tag_get(skb));
> +
> +	dcb = fdma_tx_get_dcb(fdma);
> +	if (unlikely(!dcb))
> +		return NETDEV_TX_BUSY;
> +
> +	if (!ocelot_fdma_dcb_set_tx_skb(fdma, dcb, skb)) {
> +		dev_kfree_skb_any(skb);
> +		spin_lock_bh(&fdma->tx_free_lock);
> +		list_add_tail(&dcb->node, &fdma->tx_free_dcb);
> +		spin_unlock_bh(&fdma->tx_free_lock);
> +		return NETDEV_TX_OK;
> +	}
> +
> +	spin_lock_bh(&fdma->tx_enqueue_lock);
> +
> +	if (list_empty(&fdma->tx_ongoing)) {
> +		ocelot_fdma_list_add_dcb(&fdma->tx_ongoing, dcb);
> +		fdma_activate_chan(fdma, dcb, MSCC_FDMA_INJ_CHAN);
> +	} else {
> +		ocelot_fdma_list_add_dcb(&fdma->tx_queued, dcb);
> +	}
> +
> +	spin_unlock_bh(&fdma->tx_enqueue_lock);
> +	return NETDEV_TX_OK;
> +}
> +
> +static void fdma_free_skbs_list(struct ocelot_fdma *fdma,
> +				struct list_head *list,
> +				enum dma_data_direction dir)
> +{
> +	struct ocelot_fdma_dcb *dcb;
> +
> +	if (list_empty(list))
> +		return;
> +
> +	list_for_each_entry(dcb, list, node) {
> +		if (dcb->skb) {
> +			dma_unmap_single(fdma->dev, dcb->mapping,
> +					 dcb->mapped_size, dir);
> +			dev_kfree_skb_any(dcb->skb);
> +		}
> +	}
> +}
> +
> +static int fdma_init_tx(struct ocelot_fdma *fdma)
> +{
> +	int i;
> +	struct ocelot_fdma_dcb *dcb;
> +
> +	for (i = 0; i < FDMA_MAX_SKB; i++) {
> +		dcb = fdma_dcb_alloc(fdma);
> +		if (!dcb)
> +			return -ENOMEM;
> +
> +		list_add_tail(&dcb->node, &fdma->tx_free_dcb);
> +	}
> +
> +	return 0;
> +}
> +
> +static int fdma_init_rx(struct ocelot_fdma *fdma)
> +{
> +	struct ocelot_port_private *port_priv;
> +	struct ocelot *ocelot = fdma->ocelot;
> +	struct ocelot_fdma_dcb *dcb;
> +	struct ocelot_port *port;
> +	struct net_device *ndev;
> +	int max_mtu = 0;
> +	int i;
> +	u8 port_num;
> +
> +	for (port_num = 0; port_num < ocelot->num_phys_ports; port_num++) {
> +		port = ocelot->ports[port_num];
> +		if (!port)
> +			continue;
> +
> +		port_priv = container_of(port, struct ocelot_port_private,
> +					 port);
> +		ndev = port_priv->dev;
> +
> +		ndev->needed_headroom = OCELOT_TAG_LEN;
> +		ndev->needed_tailroom = ETH_FCS_LEN;
> +
> +		if (READ_ONCE(ndev->mtu) > max_mtu)
> +			max_mtu = READ_ONCE(ndev->mtu);
> +	}
> +
> +	if (!ndev)
> +		return -ENODEV;
> +
> +	fdma->rx_buf_size = fdma_rx_compute_buffer_size(max_mtu);
> +	netif_napi_add(ndev, &fdma->napi, ocelot_fdma_napi_poll,
> +		       FDMA_WEIGHT);
> +
> +	for (i = 0; i < FDMA_MAX_SKB; i++) {
> +		dcb = fdma_dcb_alloc(fdma);
> +		if (!dcb)
> +			return -ENOMEM;
cleanup on error
> +
> +		ocelot_fdma_rx_add_dcb_sw(fdma, dcb);
> +	}
> +
> +	napi_enable(&fdma->napi);
> +
> +	return 0;
> +}
> +
> +struct ocelot_fdma *ocelot_fdma_init(struct platform_device *pdev,
> +				     struct ocelot *ocelot)
> +{
> +	struct ocelot_fdma *fdma;
> +	int ret;
> +
> +	fdma = devm_kzalloc(&pdev->dev, sizeof(*fdma), GFP_KERNEL);
> +	if (!fdma)
> +		return ERR_PTR(-ENOMEM);
> +
> +	fdma->ocelot = ocelot;
> +	fdma->base = devm_platform_ioremap_resource_byname(pdev, "fdma");
> +	if (IS_ERR_OR_NULL(fdma->base))
> +		return fdma->base;
> +
> +	fdma->dev = &pdev->dev;
> +	fdma->dev->coherent_dma_mask = DMA_BIT_MASK(32);
> +
> +	spin_lock_init(&fdma->tx_enqueue_lock);
> +	spin_lock_init(&fdma->tx_free_lock);
> +
> +	fdma_writel(fdma, MSCC_FDMA_INTR_ENA, 0);
> +
> +	fdma->irq = platform_get_irq_byname(pdev, "fdma");
> +	ret = devm_request_irq(&pdev->dev, fdma->irq, ocelot_fdma_interrupt, 0,
> +			       dev_name(&pdev->dev), fdma);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	/* Create a pool of consistent memory blocks for hardware descriptors */
> +	fdma->dcb_pool = dmam_pool_create("ocelot_fdma", &pdev->dev,
> +					  sizeof(struct ocelot_fdma_dcb),
> +					  __alignof__(struct ocelot_fdma_dcb),
> +					  0);
> +	if (!fdma->dcb_pool) {
> +		dev_err(&pdev->dev, "unable to allocate DMA descriptor pool\n");
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	INIT_LIST_HEAD(&fdma->tx_ongoing);
> +	INIT_LIST_HEAD(&fdma->tx_free_dcb);
> +	INIT_LIST_HEAD(&fdma->tx_queued);
> +	INIT_LIST_HEAD(&fdma->rx_sw);
> +	INIT_LIST_HEAD(&fdma->rx_hw);

You're leaking resources on error conditions.

> +	return fdma;
> +}
> +
> +int ocelot_fdma_start(struct ocelot_fdma *fdma)
> +{
> +	struct ocelot *ocelot = fdma->ocelot;
> +	int ret;
> +
> +	ret = fdma_init_tx(fdma);
> +	if (ret)
> +		return ret;
> +
> +	ret = fdma_init_rx(fdma);
> +	if (ret)
> +		return ret;
> +
> +	/* Reconfigure for extraction and injection using DMA */
> +	ocelot_write_rix(ocelot, QS_INJ_GRP_CFG_MODE(2), QS_INJ_GRP_CFG, 0);
> +	ocelot_write_rix(ocelot, QS_INJ_CTRL_GAP_SIZE(0), QS_INJ_CTRL, 0);
> +
> +	ocelot_write_rix(ocelot, QS_XTR_GRP_CFG_MODE(2), QS_XTR_GRP_CFG, 0);
> +
> +	fdma_writel(fdma, MSCC_FDMA_INTR_LLP, 0xffffffff);
> +	fdma_writel(fdma, MSCC_FDMA_INTR_FRM, 0xffffffff);
> +
> +	fdma_writel(fdma, MSCC_FDMA_INTR_LLP_ENA,
> +		    BIT(MSCC_FDMA_INJ_CHAN) | BIT(MSCC_FDMA_XTR_CHAN));
> +	fdma_writel(fdma, MSCC_FDMA_INTR_FRM_ENA, BIT(MSCC_FDMA_XTR_CHAN));
> +	fdma_writel(fdma, MSCC_FDMA_INTR_ENA,
> +		    BIT(MSCC_FDMA_INJ_CHAN) | BIT(MSCC_FDMA_XTR_CHAN));
> +
> +	ocelot_fdma_rx_refill(fdma);
> +
> +	return 0;
> +}
> +
> +int ocelot_fdma_stop(struct ocelot_fdma *fdma)
> +{
> +	fdma_writel(fdma, MSCC_FDMA_INTR_ENA, 0);
> +
> +	fdma_stop_channel(fdma, MSCC_FDMA_XTR_CHAN);
> +	fdma_stop_channel(fdma, MSCC_FDMA_INJ_CHAN);
> +
> +	/* Free potentially pending SKBs in DCB lists */
> +	fdma_free_skbs_list(fdma, &fdma->rx_hw, DMA_FROM_DEVICE);
> +	fdma_free_skbs_list(fdma, &fdma->rx_sw, DMA_FROM_DEVICE);
> +	fdma_free_skbs_list(fdma, &fdma->tx_ongoing, DMA_TO_DEVICE);
> +	fdma_free_skbs_list(fdma, &fdma->tx_queued, DMA_TO_DEVICE);
> +
> +	netif_napi_del(&fdma->napi);
> +
> +	return 0;
> +}
> diff --git a/drivers/net/ethernet/mscc/ocelot_fdma.h b/drivers/net/ethernet/mscc/ocelot_fdma.h
> new file mode 100644
> index 000000000000..6c5c5872abf5
> --- /dev/null
> +++ b/drivers/net/ethernet/mscc/ocelot_fdma.h
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: (GPL-2.0 OR MIT) */
> +/*
> + * Microsemi SoCs FDMA driver
> + *
> + * Copyright (c) 2021 Microchip
> + */
> +#ifndef _MSCC_OCELOT_FDMA_H_
> +#define _MSCC_OCELOT_FDMA_H_
> +
> +#include "ocelot.h"
> +
> +/**
> + * struct ocelot_fdma - FMDA struct
> + *
> + * @ocelot: Pointer to ocelot struct
> + * @base: base address of FDMA registers
> + * @dcb_pool: Pool used for DCB allocation
> + * @irq: FDMA interrupt
> + * @dev: Ocelot device
> + * @napi: napi handle
> + * @rx_buf_size: Size of RX buffer
> + * @tx_ongoing: List of DCB handed out to the FDMA
> + * @tx_queued: pending list of DCBs to be given to the hardware
> + * @tx_enqueue_lock: Lock used for tx_queued and tx_ongoing
> + * @tx_free_dcb: List of DCB available for TX
> + * @tx_free_lock: Lock used to access tx_free_dcb list
> + * @rx_hw: RX DCBs currently owned by the hardware and not completed
> + * @rx_sw: RX DCBs completed
> + */
> +struct ocelot_fdma {
> +	struct ocelot		*ocelot;
> +	void __iomem		*base;
> +	struct dma_pool		*dcb_pool;
> +	int			irq;
> +	struct device		*dev;
> +	struct napi_struct	napi;
> +	size_t			rx_buf_size;
> +
> +	struct list_head	tx_ongoing;
> +	struct list_head	tx_queued;
> +	/* Lock for tx_queued and tx_ongoing lists */
> +	spinlock_t		tx_enqueue_lock;
> +
> +	struct list_head	tx_free_dcb;
> +	/* Lock for tx_free_dcb list */
> +	spinlock_t		tx_free_lock;
> +
> +	struct list_head	rx_hw;
> +	struct list_head	rx_sw;
> +};
> +
> +struct ocelot_fdma *ocelot_fdma_init(struct platform_device *pdev,
> +				     struct ocelot *ocelot);
> +int ocelot_fdma_start(struct ocelot_fdma *fdma);
> +int ocelot_fdma_stop(struct ocelot_fdma *fdma);
> +int ocelot_fdma_inject_frame(struct ocelot_fdma *fdma, int port, u32 rew_op,
> +			     struct sk_buff *skb, struct net_device *dev);
> +
> +#endif
> diff --git a/drivers/net/ethernet/mscc/ocelot_net.c b/drivers/net/ethernet/mscc/ocelot_net.c
> index 5916492fd6d0..3971b810c5b4 100644
> --- a/drivers/net/ethernet/mscc/ocelot_net.c
> +++ b/drivers/net/ethernet/mscc/ocelot_net.c
> @@ -15,6 +15,7 @@
>   #include <net/pkt_cls.h>
>   #include "ocelot.h"
>   #include "ocelot_vcap.h"
> +#include "ocelot_fdma.h"
>   
>   #define OCELOT_MAC_QUIRKS	OCELOT_QUIRK_QSGMII_PORTS_MUST_BE_UP
>   
> @@ -457,7 +458,7 @@ static netdev_tx_t ocelot_port_xmit(struct sk_buff *skb, struct net_device *dev)
>   	int port = priv->chip_port;
>   	u32 rew_op = 0;
>   
> -	if (!ocelot_can_inject(ocelot, 0))
> +	if (!ocelot->fdma && !ocelot_can_inject(ocelot, 0))
>   		return NETDEV_TX_BUSY;
>   
>   	/* Check if timestamping is needed */
> @@ -475,9 +476,13 @@ static netdev_tx_t ocelot_port_xmit(struct sk_buff *skb, struct net_device *dev)
>   		rew_op = ocelot_ptp_rew_op(skb);
>   	}
>   
> -	ocelot_port_inject_frame(ocelot, port, 0, rew_op, skb);
> +	if (ocelot->fdma) {
> +		ocelot_fdma_inject_frame(ocelot->fdma, port, rew_op, skb, dev);
> +	} else {
> +		ocelot_port_inject_frame(ocelot, port, 0, rew_op, skb);
>   
> -	kfree_skb(skb);
> +		kfree_skb(skb);
> +	}
>   
>   	return NETDEV_TX_OK;
>   }
> diff --git a/drivers/net/ethernet/mscc/ocelot_vsc7514.c b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
> index 38103b0255b0..985d584db3a1 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"
>   
>   static const u32 ocelot_ana_regmap[] = {
> @@ -1080,6 +1081,10 @@ static int mscc_ocelot_probe(struct platform_device *pdev)
>   		ocelot->targets[io_target[i].id] = target;
>   	}
>   
> +	ocelot->fdma = ocelot_fdma_init(pdev, ocelot);
> +	if (IS_ERR(ocelot->fdma))
> +		ocelot->fdma = NULL;
> +
>   	hsio = syscon_regmap_lookup_by_compatible("mscc,ocelot-hsio");
>   	if (IS_ERR(hsio)) {
>   		dev_err(&pdev->dev, "missing hsio syscon\n");
> @@ -1139,6 +1144,12 @@ static int mscc_ocelot_probe(struct platform_device *pdev)
>   	if (err)
>   		goto out_ocelot_devlink_unregister;
>   
> +	if (ocelot->fdma) {
> +		err = ocelot_fdma_start(ocelot->fdma);
> +		if (err)
> +			goto out_ocelot_devlink_unregister;
> +	}
> +
>   	err = ocelot_devlink_sb_register(ocelot);
>   	if (err)
>   		goto out_ocelot_release_ports;
> @@ -1166,6 +1177,8 @@ static int mscc_ocelot_probe(struct platform_device *pdev)
>   out_ocelot_release_ports:
>   	mscc_ocelot_release_ports(ocelot);
>   	mscc_ocelot_teardown_devlink_ports(ocelot);
> +	if (ocelot->fdma)
> +		ocelot_fdma_stop(ocelot->fdma);
>   out_ocelot_devlink_unregister:
>   	ocelot_deinit(ocelot);
>   out_put_ports:
> @@ -1179,6 +1192,8 @@ static int mscc_ocelot_remove(struct platform_device *pdev)
>   {
>   	struct ocelot *ocelot = platform_get_drvdata(pdev);
>   
> +	if (ocelot->fdma)
> +		ocelot_fdma_stop(ocelot->fdma);
>   	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 b3381c90ff3e..33e1559bdea3 100644
> --- a/include/soc/mscc/ocelot.h
> +++ b/include/soc/mscc/ocelot.h
> @@ -695,6 +695,8 @@ 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;
>   };
>   
>   struct ocelot_policer {
>