lkml.org 
[lkml]   [2021]   [Aug]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RESEND PATCH 4/4] can: c_can: cache frames to operate as a true FIFO
On 05.08.2021 22:16:06, Dario Binacchi wrote:
> > > --- 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?
[...]
> > > @@ -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.

How? You only use the spin_lock in c_can_start_xmit(), but not anywhere
else.

> Enabling the transmission of cached messages occur inside interrupt

The call chain is c_can_poll() -> c_can_do_tx(), and c_can_poll() is
called from NAPI, which is not the IRQ handler.

> and the use of the IF_RX interface, which would avoid the use of the
> spinlock, has not been validated by the tests.

What do you mean be has not been validated?

The driver already uses IF_RX to avoid concurrent access in
c_can_do_tx() for c_can_inval_tx_object() [1], why not use IF_RX for
c_can_object_put(), too?

[1] https://lore.kernel.org/r/20210302215435.18286-4-dariobin@libero.it

Marc

--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2021-08-06 11:27    [W:1.966 / U:0.016 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site