Re: [RESEND PATCH 4/4] can: c_can: cache frames to operate as a true FIFO

Dario Binacchi
2021-08-05T20:16:09Z

Hi Marc,

> Il 04/08/2021 11:45 Marc Kleine-Budde <mkl@pengutronix.de> ha scritto:
>
>
> On 25.07.2021 18:11:50, Dario Binacchi wrote:
> > diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
> > index 8fe7e2138620..fc499a70b797 100644
> > --- a/drivers/net/can/c_can/c_can.h
> > +++ b/drivers/net/can/c_can/c_can.h
> > @@ -200,6 +200,7 @@ struct c_can_priv {
> > atomic_t sie_pending;
> > unsigned long tx_dir;
> > int last_status;
> > + spinlock_t tx_lock;
>
> What does the spin lock protect?
>
> > struct c_can_tx_ring tx;
> > u16 (*read_reg)(const struct c_can_priv *priv, enum reg index);
> > void (*write_reg)(const struct c_can_priv *priv, enum reg index, u16 val);
> > @@ -236,4 +237,9 @@ static inline u8 c_can_get_tx_tail(const struct c_can_tx_ring *ring)
> > return ring->tail & (ring->obj_num - 1);
> > }
> >
> > +static inline u8 c_can_get_tx_free(const struct c_can_tx_ring *ring)
> > +{
> > + return ring->obj_num - (ring->head - ring->tail);
> > +}
> > +
> > #endif /* C_CAN_H */
> > diff --git a/drivers/net/can/c_can/c_can_main.c b/drivers/net/can/c_can/c_can_main.c
> > index 451ac9a9586a..4c061fef002c 100644
> > --- a/drivers/net/can/c_can/c_can_main.c
> > +++ b/drivers/net/can/c_can/c_can_main.c
> > @@ -427,20 +427,6 @@ static void c_can_setup_receive_object(struct net_device *dev, int iface,
> > c_can_object_put(dev, iface, obj, IF_COMM_RCV_SETUP);
> > }
> >
> > -static u8 c_can_get_tx_free(const struct c_can_tx_ring *ring)
> > -{
> > - u8 head = c_can_get_tx_head(ring);
> > - u8 tail = c_can_get_tx_tail(ring);
> > -
> > - /* This is not a FIFO. C/D_CAN sends out the buffers
> > - * prioritized. The lowest buffer number wins.
> > - */
> > - if (head < tail)
> > - return 0;
> > -
> > - return ring->obj_num - head;
> > -}
> > -
> > static bool c_can_tx_busy(const struct c_can_priv *priv,
> > const struct c_can_tx_ring *tx_ring)
> > {
> > @@ -470,7 +456,7 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
> > struct can_frame *frame = (struct can_frame *)skb->data;
> > struct c_can_priv *priv = netdev_priv(dev);
> > struct c_can_tx_ring *tx_ring = &priv->tx;
> > - u32 idx, obj;
> > + u32 idx, obj, cmd = IF_COMM_TX;
> >
> > if (can_dropped_invalid_skb(dev, skb))
> > return NETDEV_TX_OK;
> > @@ -483,7 +469,11 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
> > if (c_can_get_tx_free(tx_ring) == 0)
> > netif_stop_queue(dev);
> >
> > - obj = idx + priv->msg_obj_tx_first;
> > + spin_lock_bh(&priv->tx_lock);
>
> What does the spin_lock protect? The ndo_start_xmit function is properly
> serialized by the networking core.
>

The spin_lock protects the access to the IF_TX interface. Enabling the transmission
of cached messages occur inside interrupt and the use of the IF_RX interface,
which would avoid the use of the spinlock, has not been validated by
the tests.

Thanks and regards,
Dario

> Otherwise the patch looks good!
>
> Marc
>
> --
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