linux-kernel - Re: [PATCH net-next v5 4/4] net: ocelot: add FDMA support

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Date:   Tue, 7 Dec 2021 13:52:01 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Clément Léger <clement.leger@...tlin.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Denis Kirjanov <dkirjanov@...e.de>,
        Julian Wiedmann <jwi@...ux.ibm.com>
Subject: Re: [PATCH net-next v5 4/4] net: ocelot: add FDMA support

On Tue, Dec 07, 2021 at 10:08:53AM +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@...tlin.com>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Signed-off-by: Clément Léger <clement.leger@...tlin.com>
> ---

> +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(ocelot, dma, MSCC_FDMA_INJ_CHAN);
> +	} else {
> +		/* Chain the DCBs */
> +		dcb->llp = ocelot_fdma_idx_dma(tx_ring->dcbs_dma, next_idx);
> +	}
> +	skb_tx_timestamp(skb);
> +
> +	tx_ring->next_to_use = next_idx;

You've decided against moving these before ocelot_fdma_activate_chan?
The skb may be freed by ocelot_fdma_tx_cleanup() before
skb_tx_timestamp() has a chance to run, is this not true?

> +}
> diff --git a/drivers/net/ethernet/mscc/ocelot_vsc7514.c b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
> index cd3eb101f159..bee883a0b5b8 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"
>
>  #define VSC7514_VCAP_POLICER_BASE			128
> @@ -275,6 +276,18 @@ static const u32 ocelot_ptp_regmap[] = {
>  	REG(PTP_CLK_CFG_ADJ_FREQ,			0x0000a8),
>  };
>
> +static const u32 ocelot_fdma_regmap[] = {
> +	REG(PTP_PIN_CFG,				0x000000),
> +	REG(PTP_PIN_TOD_SEC_MSB,			0x000004),
> +	REG(PTP_PIN_TOD_SEC_LSB,			0x000008),
> +	REG(PTP_PIN_TOD_NSEC,				0x00000c),
> +	REG(PTP_PIN_WF_HIGH_PERIOD,			0x000014),
> +	REG(PTP_PIN_WF_LOW_PERIOD,			0x000018),
> +	REG(PTP_CFG_MISC,				0x0000a0),
> +	REG(PTP_CLK_CFG_ADJ_CFG,			0x0000a4),
> +	REG(PTP_CLK_CFG_ADJ_FREQ,			0x0000a8),
> +};

drivers/net/ethernet/mscc/ocelot_vsc7514.c:279:18: warning: ‘ocelot_fdma_regmap’ defined but not used [-Wunused-const-variable=]
  279 | static const u32 ocelot_fdma_regmap[] = {
      |                  ^~~~~~~~~~~~~~~~~~

Not to mention this isn't even the FDMA regmap.

> +
>  static const u32 ocelot_dev_gmii_regmap[] = {
>  	REG(DEV_CLOCK_CFG,				0x0),
>  	REG(DEV_PORT_MISC,				0x4),
> @@ -1048,6 +1061,7 @@ static int mscc_ocelot_probe(struct platform_device *pdev)
>  		{ S1, "s1" },
>  		{ S2, "s2" },
>  		{ PTP, "ptp", 1 },
> +		{ FDMA, "fdma", 1 },
>  	};