Subject: Re: [PATCH] ARM: OMAP: AM33XX: CAN: d_can: Add support for Bosch D_CAN controller

From: Marc Kleine-Budde <[email-masked]>
Date: Tue, 03 Apr 2012 15:49:32 +0200

On 04/03/2012 03:41 PM, AnilKumar, Chimata wrote:
> 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 <[email-masked]>
>>
>> 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.

How many bits in these 32 bit registers are used?

> * Some of the registers, bit masks are different, so we have to add
>   checks on every API for differentiating the kind of device

Which registers are this? Can you give us an example?

> * 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.

Which of these features are used in you driver?

> * Wait timings while init bit set/reset during bit-timing initialization
>   are different in both the cases

That's not the hot code path, so some ifs shouldn't hurt.

> * bittiming configurations are different.

see above.

Marc
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