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Date: Tue, 14 Apr 2020 03:07:09 +0000
From: Andy Duan <fugang.duan@....com>
To: Andrew Lunn <andrew@...n.ch>, David Miller <davem@...emloft.net>
CC: netdev <netdev@...r.kernel.org>,
Chris Healy <Chris.Healy@....aero>,
Chris Heally <cphealy@...il.com>
Subject: RE: [EXT] [PATCH] net: ethernet: fec: Replace interrupt driven MDIO
with polled IO
From: Andrew Lunn <andrew@...n.ch> Sent: Tuesday, April 14, 2020 8:46 AM
> Measurements of the MDIO bus have shown that driving the MDIO bus using
> interrupts is slow. Back to back MDIO transactions take about 90uS, with
> 25uS spent performing the transaction, and the remainder of the time the bus
> is idle.
>
> Replacing the completion interrupt with polled IO results in back to back
> transactions of 40uS. The polling loop waiting for the hardware to complete
> the transaction takes around 27uS. Which suggests interrupt handling has an
> overhead of 50uS, and polled IO nearly halves this overhead, and doubles the
> MDIO performance.
>
Although the mdio performance is better, but polling IO by reading register
cause system/bus loading more heavy.
So I don't think it is valuable to change interrupt mode to polling mode.
Thanks,
Andy
> Suggested-by: Chris Heally <cphealy@...il.com>
> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> ---
> drivers/net/ethernet/freescale/fec.h | 4 +-
> drivers/net/ethernet/freescale/fec_main.c | 69 ++++++++++++-----------
> 2 files changed, 37 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/net/ethernet/freescale/fec.h
> b/drivers/net/ethernet/freescale/fec.h
> index bd898f5b4da5..4c8e7f57957a 100644
> --- a/drivers/net/ethernet/freescale/fec.h
> +++ b/drivers/net/ethernet/freescale/fec.h
> @@ -376,8 +376,7 @@ struct bufdesc_ex {
> #define FEC_ENET_TS_AVAIL ((uint)0x00010000)
> #define FEC_ENET_TS_TIMER ((uint)0x00008000)
>
> -#define FEC_DEFAULT_IMASK (FEC_ENET_TXF | FEC_ENET_RXF |
> FEC_ENET_MII) -#define FEC_NAPI_IMASK FEC_ENET_MII
> +#define FEC_DEFAULT_IMASK (FEC_ENET_TXF | FEC_ENET_RXF)
> #define FEC_RX_DISABLED_IMASK (FEC_DEFAULT_IMASK &
> (~FEC_ENET_RXF))
>
> /* ENET interrupt coalescing macro define */ @@ -537,7 +536,6 @@ struct
> fec_enet_private {
> int link;
> int full_duplex;
> int speed;
> - struct completion mdio_done;
> int irq[FEC_IRQ_NUM];
> bool bufdesc_ex;
> int pause_flag;
> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> b/drivers/net/ethernet/freescale/fec_main.c
> index c1c267b61647..48ac0a3a4eb0 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -938,8 +938,8 @@ fec_restart(struct net_device *ndev)
> writel((__force u32)cpu_to_be32(temp_mac[1]),
> fep->hwp + FEC_ADDR_HIGH);
>
> - /* Clear any outstanding interrupt. */
> - writel(0xffffffff, fep->hwp + FEC_IEVENT);
> + /* Clear any outstanding interrupt, except MDIO. */
> + writel((0xffffffff & ~FEC_ENET_MII), fep->hwp + FEC_IEVENT);
>
> fec_enet_bd_init(ndev);
>
> @@ -1085,7 +1085,7 @@ fec_restart(struct net_device *ndev)
> if (fep->link)
> writel(FEC_DEFAULT_IMASK, fep->hwp + FEC_IMASK);
> else
> - writel(FEC_ENET_MII, fep->hwp + FEC_IMASK);
> + writel(0, fep->hwp + FEC_IMASK);
>
> /* Init the interrupt coalescing */
> fec_enet_itr_coal_init(ndev);
> @@ -1599,6 +1599,10 @@ fec_enet_interrupt(int irq, void *dev_id)
> irqreturn_t ret = IRQ_NONE;
>
> int_events = readl(fep->hwp + FEC_IEVENT);
> +
> + /* Don't clear MDIO events, we poll for those */
> + int_events &= ~FEC_ENET_MII;
> +
> writel(int_events, fep->hwp + FEC_IEVENT);
> fec_enet_collect_events(fep, int_events);
>
> @@ -1606,16 +1610,12 @@ fec_enet_interrupt(int irq, void *dev_id)
> ret = IRQ_HANDLED;
>
> if (napi_schedule_prep(&fep->napi)) {
> - /* Disable the NAPI interrupts */
> - writel(FEC_NAPI_IMASK, fep->hwp +
> FEC_IMASK);
> + /* Disable interrupts */
> + writel(0, fep->hwp + FEC_IMASK);
> __napi_schedule(&fep->napi);
> }
> }
>
> - if (int_events & FEC_ENET_MII) {
> - ret = IRQ_HANDLED;
> - complete(&fep->mdio_done);
> - }
> return ret;
> }
>
> @@ -1765,11 +1765,26 @@ static void fec_enet_adjust_link(struct
> net_device *ndev)
> phy_print_status(phy_dev); }
>
> +static int fec_enet_mdio_wait(struct fec_enet_private *fep) {
> + int retries = 10000;
> + uint ievent;
> +
> + while (retries--) {
> + ievent = readl(fep->hwp + FEC_IEVENT);
> + if (ievent & FEC_ENET_MII) {
> + writel(FEC_ENET_MII, fep->hwp +
> FEC_IEVENT);
> + return 0;
> + }
> + }
> +
> + return -ETIMEDOUT;
> +}
> +
> static int fec_enet_mdio_read(struct mii_bus *bus, int mii_id, int regnum) {
> struct fec_enet_private *fep = bus->priv;
> struct device *dev = &fep->pdev->dev;
> - unsigned long time_left;
> int ret = 0, frame_start, frame_addr, frame_op;
> bool is_c45 = !!(regnum & MII_ADDR_C45);
>
> @@ -1777,8 +1792,6 @@ static int fec_enet_mdio_read(struct mii_bus *bus,
> int mii_id, int regnum)
> if (ret < 0)
> return ret;
>
> - reinit_completion(&fep->mdio_done);
> -
> if (is_c45) {
> frame_start = FEC_MMFR_ST_C45;
>
> @@ -1790,11 +1803,9 @@ static int fec_enet_mdio_read(struct mii_bus
> *bus, int mii_id, int regnum)
> fep->hwp + FEC_MII_DATA);
>
> /* wait for end of transfer */
> - time_left =
> wait_for_completion_timeout(&fep->mdio_done,
> - usecs_to_jiffies(FEC_MII_TIMEOUT));
> - if (time_left == 0) {
> + ret = fec_enet_mdio_wait(fep);
> + if (ret) {
> netdev_err(fep->netdev, "MDIO address write
> timeout\n");
> - ret = -ETIMEDOUT;
> goto out;
> }
>
> @@ -1813,11 +1824,9 @@ static int fec_enet_mdio_read(struct mii_bus
> *bus, int mii_id, int regnum)
> FEC_MMFR_TA, fep->hwp + FEC_MII_DATA);
>
> /* wait for end of transfer */
> - time_left = wait_for_completion_timeout(&fep->mdio_done,
> - usecs_to_jiffies(FEC_MII_TIMEOUT));
> - if (time_left == 0) {
> + ret = fec_enet_mdio_wait(fep);
> + if (ret) {
> netdev_err(fep->netdev, "MDIO read timeout\n");
> - ret = -ETIMEDOUT;
> goto out;
> }
>
> @@ -1835,7 +1844,6 @@ static int fec_enet_mdio_write(struct mii_bus *bus,
> int mii_id, int regnum, {
> struct fec_enet_private *fep = bus->priv;
> struct device *dev = &fep->pdev->dev;
> - unsigned long time_left;
> int ret, frame_start, frame_addr;
> bool is_c45 = !!(regnum & MII_ADDR_C45);
>
> @@ -1845,8 +1853,6 @@ static int fec_enet_mdio_write(struct mii_bus *bus,
> int mii_id, int regnum,
> else
> ret = 0;
>
> - reinit_completion(&fep->mdio_done);
> -
> if (is_c45) {
> frame_start = FEC_MMFR_ST_C45;
>
> @@ -1858,11 +1864,9 @@ static int fec_enet_mdio_write(struct mii_bus
> *bus, int mii_id, int regnum,
> fep->hwp + FEC_MII_DATA);
>
> /* wait for end of transfer */
> - time_left =
> wait_for_completion_timeout(&fep->mdio_done,
> - usecs_to_jiffies(FEC_MII_TIMEOUT));
> - if (time_left == 0) {
> + ret = fec_enet_mdio_wait(fep);
> + if (ret) {
> netdev_err(fep->netdev, "MDIO address write
> timeout\n");
> - ret = -ETIMEDOUT;
> goto out;
> }
> } else {
> @@ -1878,12 +1882,9 @@ static int fec_enet_mdio_write(struct mii_bus
> *bus, int mii_id, int regnum,
> fep->hwp + FEC_MII_DATA);
>
> /* wait for end of transfer */
> - time_left = wait_for_completion_timeout(&fep->mdio_done,
> - usecs_to_jiffies(FEC_MII_TIMEOUT));
> - if (time_left == 0) {
> + ret = fec_enet_mdio_wait(fep);
> + if (ret)
> netdev_err(fep->netdev, "MDIO write timeout\n");
> - ret = -ETIMEDOUT;
> - }
>
> out:
> pm_runtime_mark_last_busy(dev);
> @@ -2079,6 +2080,9 @@ static int fec_enet_mii_init(struct platform_device
> *pdev)
>
> writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED);
>
> + /* Clear any pending transaction complete indication */
> + writel(FEC_ENET_MII, fep->hwp + FEC_IEVENT);
> +
> fep->mii_bus = mdiobus_alloc();
> if (fep->mii_bus == NULL) {
> err = -ENOMEM;
> @@ -3583,7 +3587,6 @@ fec_probe(struct platform_device *pdev)
> fep->irq[i] = irq;
> }
>
> - init_completion(&fep->mdio_done);
> ret = fec_enet_mii_init(pdev);
> if (ret)
> goto failed_mii_init;
> --
> 2.26.0
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