linux-kernel - RE: [PATCH] ARM: OMAP: AM33XX: CAN: d_can: Add support for Bosch D

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Date:	Tue, 3 Apr 2012 13:41:28 +0000
From:	"AnilKumar, Chimata" <anilkumar@...com>
To:	Wolfgang Grandegger <wg@...ndegger.com>
CC:	"socketcan@...tkopp.net" <socketcan@...tkopp.net>,
	"m.kleine-budde@...gutronix.de" <m.kleine-budde@...gutronix.de>,
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Gole, Anant" <anantgole@...com>, "Nori, Sekhar" <nsekhar@...com>
Subject: RE: [PATCH] ARM: OMAP: AM33XX: CAN: d_can: Add support for Bosch
 D_CAN controller

Hi Wolfgang,

Thanks for reviewing the patch

On Tue, Apr 03, 2012 at 18:14:55, Wolfgang Grandegger wrote:
> On 04/03/2012 02:32 PM, AnilKumar Ch wrote:
> > This patch adds the support for Bosch D_CAN controller.
> > 
> > Bosch D_CAN controller is a full-CAN implementation compliant to
> > CAN protocol version 2.0 part A and B. Bosch D_CAN user manual
> > can be obtained from: http://www.semiconductors.bosch.de/media/
> > en/pdf/ipmodules_1/can/d_can_users_manual_111.pdf
> > 
> > D_CAN device is used on many SoCs like AM335x, DM8148 and DM813x
> > EVMs from TI, D_CAN details on AM335x can be accessed from:
> > http://www.ti.com/lit/ug/spruh73c/spruh73c.pdf
> > 
> > D_CAN can be configurable for 16, 32, 64 and 128 message objects.
> > The driver implementation is based on 64 message objects.
> > 
> > Following are the design choices made while writing the controller
> > driver:
> > 1. Interface Register set IF0 has be used for receive and IF1 is
> >    used for transmit message objects.
> > 2. Out of the total Message objects available, half of it are kept
> >    aside for RX purposes and the rest for TX purposes.
> > 3. NAPI implementation is such that both the TX and RX paths
> >    functions in polling mode.
> > 
> > Signed-off-by: AnilKumar Ch <anilkumar@...com>
> 
> Please explain why this CAN controller cannot be handled by the existing
> C_CAN driver, eventually with some extensions. The register layout seems
> almost identical, at least.
> 
> Wolfgang.
> 

These are the some of the pointers I can say, why I had gone for separate
file instead of existing driver:
* In case of D_CAN driver we can see all the registers are 32bit length
  but in case of C_CAN registers are in 16bit length.
* Some of the registers, bit masks are different, so we have to add
  checks on every API for differentiating the kind of device
* In case of D_CAN we have some extra features like direct message RAM
  access, DMA support, TX/RX pins can be used as GPIO lines (if applicable),
  more interrupt lines and three sets of interface registers.
* Wait timings while init bit set/reset during bit-timing initialization
  are different in both the cases
* bittiming configurations are different.

Thanks
AnilKumar
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