Re: [PATCH RESEND] net: can: Introduce MEN 16Z192-00 CAN controller driver

[Wolfgang Grandegger]

Am 09.08.2016 um 08:10 schrieb Andreas Werner:
> On Mon, Aug 08, 2016 at 04:35:34PM +0200, Wolfgang Grandegger wrote:
> > Am 08.08.2016 um 16:05 schrieb Andreas Werner:
> > > On Mon, Aug 08, 2016 at 02:28:39PM +0200, Wolfgang Grandegger wrote:

---snip---

> > > > > > > +
> > > > > > > +	ndev = alloc_candev(sizeof(struct men_z192), 1);
> > > > > >
> > > > > > You specify here one echo_skb but it's not used anywhere. Local loopback
> > > > > > seems not to be implemented.
> > > > >
> > > > > Agree with you, will set it to "0".
> > > >
> > > > No, the local loopback is mandetory!
> > >
> > > Hm ok, but if i check alloc_candev() in drivers/net/can/dev.c
> > > it is not mandatory. In the Documentation/networking/can.txt
> > > there is also a "should" and a fallback mechnism if the driver
> > > does not support the local loopback.
> >
> > Well, s/driver/hardware/ ! Local loopback is the preferred mechanism.
>
> Sure...
>
> > > I'm currently ok with this fallback mechanism.
> > >
> > > Anyway I am not sure that the driver can handle the echo skb correctly.
> > > If i understand it correctly, the can_get_echo_skb() is normally called
> > > on a "TX done IRQ" to get the skb and loop it back.
> > > I do not have such a "TX done IRQ" and have not implemented implemented
> > > and added the local looback.
> >
> > What does "MEN_Z192_TFLG_TXIF" signal?
>
> It is not a "TX Done" IRQ, it is the tx buffer level IRQ.
> The IRQ is triggered when the number of available tx buffer entries is as
> configured with txlvl. (after the buffer was full)
>
> Example:
> txlvl = 0
> tx buffer has 255 entries.
>
> -> The IRQ is triggered as soon as 1 frame got transmitted (254 entries).
>
> ---
>
> txlvl = 254
> tx buffer has 255 entries.
>
> -> The IRQ is triggered as soon as the buffer has one entry and it got transmitted
>
>
> > > May be I can put and get the echo skb within the xmit function?
> > > Does this make sense?
> >
> > It only makes sense if the driver knows when one or more transfers are done.
>
> Then i do not think that I can use the txlvl IRQ in this case and need to use
> the fallback mechanism.


You could store "MEN_Z192_TX_BUF_CNT(readl(&regs->rx_tx_sts))" in the 
start_xmit function and check again in the isr function to find out how 
much transfers have been transmitted in the meantime. Does it make sense?

Wolfgang.