Re: [PATCH v4 3/4] can: kvaser_usb: Add support for the Usbcan-II family

Ahmed S. Darwish
2015-01-18T20:12:28Z

Hi!

On Mon, Jan 12, 2015 at 02:53:02PM +0100, Olivier Sobrie wrote:
> Hello,
>
> On Sun, Jan 11, 2015 at 03:36:12PM -0500, Ahmed S. Darwish wrote:
> > From: Ahmed S. Darwish <ahmed.darwish@valeo.com>
> >

...

> > @@ -98,7 +128,13 @@
> > #define CMD_START_CHIP_REPLY 27
> > #define CMD_STOP_CHIP 28
> > #define CMD_STOP_CHIP_REPLY 29
> > -#define CMD_GET_CARD_INFO2 32
> > +#define CMD_READ_CLOCK 30
> > +#define CMD_READ_CLOCK_REPLY 31
>
> These two defines are not used.
>

They were added for completeness: the only gap in our continuous
sequence of command IDs from 12 to 39 ;-) No big deal, to be
removed in the next submission.

...

> > +
> > +struct kvaser_msg_tx_acknowledge_header {
> > + u8 channel;
> > + u8 tid;
> > +};
>
> Is this struct really needed? Can't you simply use
> leaf_msg_tx_acknowledge or usbcan_msg_tx_acknowledge
> structures to read the header.
> Same for kvaser_msg_rx_can_header.
>

They're added to ensure type-safety throughout the code. Basically
they're the common part of a command that has different wire format
between the Leaf and the USBCan, but share a common header. Such
notation was only added when it was strictly necessary.

For example, there are three functions where 'rx_can_header' is
referenced in the driver, and one function where 'tx_acknowledge_header'
is referenced. Without such header structure, I'll have to sprinkle
3 to 4 extra blocks of:

switch (dev->family) {
case KVASER_LEAF:
case KVASER_USBCAN:
}

which would be _really_ ugly. The *_header notation ensures that, in
the body of each function, we're accessing the fields in a very safe
manner.

Thanks,
Darwish