netdev - RE: [MeeGo-Dev][PATCH] Topcliff: Update PCH

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Date:	Thu, 12 Aug 2010 14:29:32 +0800
From:	"Wang, Qi" <qi.wang@...el.com>
To:	Oliver Hartkopp <socketcan@...tkopp.net>
CC:	Greg KH <gregkh@...e.de>, Daniel Baluta <daniel.baluta@...il.com>,
	Masayuki Ohtak <masa-korg@....okisemi.com>,
	"meego-dev@...go.com" <meego-dev@...go.com>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	"socketcan-core@...ts.berlios.de" <socketcan-core@...ts.berlios.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Khor, Andrew Chih Howe" <andrew.chih.howe.khor@...el.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"Wang, Yong Y" <yong.y.wang@...el.com>
Subject: RE: [MeeGo-Dev][PATCH] Topcliff: Update PCH_CAN driver to 2.6.35

> -----Original Message-----
> From: Oliver Hartkopp [mailto:socketcan@...tkopp.net]
> Sent: Thursday, August 12, 2010 2:26 PM
> To: Wang, Qi
> Cc: Greg KH; Daniel Baluta; Masayuki Ohtak; meego-dev@...go.com;
> Wolfgang Grandegger; socketcan-core@...ts.berlios.de;
> netdev@...r.kernel.org; Khor, Andrew Chih Howe; arjan@...ux.intel.com;
> Wang, Yong Y
> Subject: Re: [MeeGo-Dev][PATCH] Topcliff: Update PCH_CAN driver to 2.6.35
> 
> On 12.08.2010 04:04, Greg KH wrote:
> > On Thu, Aug 12, 2010 at 09:42:27AM +0800, Wang, Qi wrote:
> 
> >>> 2. Why don't you use kernel existing kfifo infrastructure? ([2]).
> >> Just take a look at kfifo.h. This structure has been changed. I
> >> remembered there was a spin_lock from kfifo previously. Currently it's
> >> been removed, good.
> >> OKI-sans, would you please take a look at ./include/linux/kfifo.h, and try to
> use this structure and APIs?
> >>
> >> Daniel,
> >>
> >> We're anxious to integrate those codes now. Perhaps it'll take us
> >> quite a long time to use kfifo. How about implementing it with the
> >> next version?
> >
> > What do you mean by this?  Code isn't merged into the tree unless it is
> > correct.  Please fix this now, it's not that big of a deal.
> >
> 
> Hello Qi,
> 
> i generally wonder what this FIFO is used for??
> 
> For me it looks like a artifact from a former chardev implementation, as
> several other code sniplets do (see comments from Wolfgang and Marc).
> 
> The network driver model is used for CAN drivers and therefore all the
> infrastructure for queueing inbound and outbound network traffic should be
> used from the Kernel like all other CAN drivers and all other ethernet drivers
> do.
> 
> Additionally there is a powerful infrastructure to support the special
> functions of CAN netdevices (like setting of bittimings, listen-only modes, or
> to produce CAN driver states etc.), that's part of the CAN drivers in
> drivers/net/can/ since it has gone mainline.
> 
> CAN netdevices are intentionally dumb (like the original ethernet adapters).
> This allows a simple driver interface between the kernel and the hardware
> driver, e.g. for queueing CAN frames. CAN drivers don't use any hardware
> rx-filtering(!) due to multiuser requirements and it's a vital requirement
> that the frames are not re-ordered on sending (by the 'some magic' CAN
> controller dealing with CAN-ID priorities, e.g. see tx-path in the MSCAN driver).
> 
> From my perspective about 70% of your code is obsolete, as you implemented
> tricky details (like FIFOs, bittiming tables or magic filter handlings),
> that's not needed at all.
> 
> Please take a look at the SJA1000 driver (for a low complex CAN controller) or
> at the TI driver (for a higher complex CAN controller) how these drivers
> handle the specialties of each hardware. And read some documentation in
> Documentation/networking/can.txt to get an impression about the concepts of
> the CAN implementation in the Linux Kernel and the CAN netdevices.
> 
> I strongly assume that your driver would be about 30 kBytes of code fitting
> into a single c-file like the ti_hecc.c does. And that's definitely easier for
> us to review and easier for you to maintain in the future ...
> 
> Thanks & best regards,
> Oliver
Thank you for your commits.