netdev - Re: [PATCH] can: kvaser_usb: Add support for the Usbcan-II family

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Date:	Tue, 30 Dec 2014 10:33:26 -0500
From:	"Ahmed S. Darwish" <darwish.07@...il.com>
To:	Olivier Sobrie <olivier@...rie.be>
Cc:	Oliver Hartkopp <socketcan@...tkopp.net>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Linux-CAN <linux-can@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] can: kvaser_usb: Add support for the Usbcan-II family

On Sun, Dec 28, 2014 at 10:51:34PM +0100, Olivier Sobrie wrote:
[...]
> > > >  
> > > > +	if (LEAF_PRODUCT_ID(id->idProduct)) {
> > > > +		dev->family = KVASER_LEAF;
> > > > +		dev->max_channels = LEAF_MAX_NET_DEVICES;
> > > > +	} else if (USBCAN_PRODUCT_ID(id->idProduct)) {
> > > > +		dev->family = KVASER_USBCAN;
> > > > +		dev->max_channels = USBCAN_MAX_NET_DEVICES;
> > > > +	} else {
> > > > +		dev_err(&intf->dev, "Product ID (%d) does not belong to any "
> > > > +				    "known Kvaser USB family", id->idProduct);
> > > > +		return -ENODEV;
> > > > +	}
> > > > +
> > > 
> > > Is it really required to keep max_channels in the kvaser_usb structure?
> > > If I looked correctly, you use this variable as a replacement for
> > > MAX_NET_DEVICES in the code and MAX_NET_DEVICES is only used in probe
> > > and disconnect functions. I think it can even be replaced by nchannels
> > > in the disconnect path. So I also think that it don't need to be in the
> > > kvaser_usb structure.
> > > 
> > 
> > hmmm.. given the current state of error arbitration explained
> > above, where I cannot accept a dev->nchannels > 2, I guess we
> > have two options:
> > 
> > a) Remove max_channels, and hardcode the channels count
> > correctness logic as follows:
> > 
> >         dev->nchannels = msg.u.cardinfo.nchannels;
> >         if ((dev->family == USBCAN && dev->nchannels > USBCAN_MAX_NET_DEVICES)
> >             || (dev->family == LEAF && dev->nchannels > LEAF_MAX_NET_DEVICES))
> >                 return -EINVAL
> > 
> > b) Leave max_channels in 'struct kvaser_usb' as is.
> > 
> > I personally prefer the solution at 'b)' but I can do it as
> > in 'a)' if you prefer :-)
> 
> Keeping max_channels in the kvaser_usb structure is useless because it
> is only used in one function that is called in the probe function.
> 
> I would prefer to have:
> 	if (dev->nchannels > MAX_NET_DEVICES)
> 		return -EINVAL
> 
> 	if ((dev->family == USBCAN) &&
> 	    (dev->nchannels > MAX_USBCAN_NET_DEVICES))
> 		return -EINVAL
> 
> You can remove LEAF_MAX_NET_DEVICES which is not used, keep
> MAX_NET_DEVICES equals to 3 and remove the MAX() macro.
> The test specific to the USBCAN family can eventually be moved in the
> kvaser_usb_probe() function.
> 

Quite nice, will do it that way in v3.

Regards,
Darwish
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