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Subject: Re: [RFC PATCH 1/3] can: m_can: Create m_can core to leverage common
 code
To:     Wolfgang Grandegger <wg@grandegger.com>, <mkl@pengutronix.de>,
        <davem@davemloft.net>
CC:     <linux-can@vger.kernel.org>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20181010142055.25271-1-dmurphy@ti.com>
 <20181010142055.25271-2-dmurphy@ti.com>
 <52811b27-00c0-f5e2-2b18-608ccf846723@grandegger.com>
 <349ef8be-f4c7-25cc-2c33-7ce1fd0b0f40@ti.com>
 <9003a544-83cf-7dce-7f14-4abd292d470e@grandegger.com>
From:   Dan Murphy <dmurphy@ti.com>
Message-ID: <b73e200c-8a6b-00e0-dabc-af3245cc36fd@ti.com>
Date:   Wed, 9 Jan 2019 14:58:23 -0600
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Wolfgang

On 11/3/18 5:45 AM, Wolfgang Grandegger wrote:
> Hello Dan,
> 
> Am 31.10.2018 um 21:15 schrieb Dan Murphy:
>> Wolfgang
>>
>> Thanks for the review
>>
>> On 10/27/2018 09:19 AM, Wolfgang Grandegger wrote:
>>> Hello Dan,
>>>
>>> for the RFC, could you please just do the necessary changes to the
>>> existing code. We can discuss about better names, etc. later. For
>>> the review if the common code I quickly did:
>>>
>>>   mv m_can.c m_can_platform.c
>>>   mv m_can_core.c m_can.c
>>>
>>> The file names are similar to what we have for the C_CAN driver.
>>>
>>>   s/classdev/priv/
>>>   variable name s/m_can_dev/priv/
>>>
>>> Then your patch 1/3 looks as shown below. I'm going to comment on that
>>> one. The comments start with "***"....
>>>
>>
>> So you would like me to align the names with the c_can driver?
> 
> That would be the obvious choice.
>> <snip>
>>>
>>> *** I didn't review the rest of the patch for now.
>>>
>>
>> snipped the code to reply to the comment.
>>
>>> Looking to the generic code, you didn't really change the way
>>> the driver is accessing the registers. Also the interrupt handling
>>> and rx polling is as it was before. Does that work properly using
>>> the SPI interface of the TCAN4x5x?
>>
>> I don't want to change any of that yet.  Maybe my cover letter was not clear
>> or did not go through.
>>
>> But the intention was just to break out the functionality to create a MCAN framework
>> that can be used by devices that contain the Bosch MCAN core and provider their own protocal to access
>> the registers in the device.
>>
>> I don't want to do any functional changes at this time on the IP code itself until we have a framework.
>> There should be no regression in the io mapped code.
>>
>> I did comment on the interrupt handling and asked if a threaded work queue would affect CAN timing.
>> For the original TCAN driver this was the way it was implemented.
> 
> Do threaded interrupts with RX polling make sense? I think we need a
> common interface allowing to select hard-irqs+napi or threaded-irqs.
> 

I have been working on this code for about a month now and I am *not happy* with the amount of change that needs
to be done to make the m_can a framework.

I can tx/rx frames from another CAN device to the TCAN part but I have not even touched the iomapped code.

The challenging part is that the m_can code that is currently available does not have to worry about atomic context because
there is no peripheral waiting.  Since the TCAN is a peripheral device we need to take into about the hard waits in IRQ context
as well as the atomic context.  Doing this creates many deltas in the base code that may break iomapped devices.  I have had to 
add the thread_irqs and now I am in the midst of the issue you brought up with napi.  I would have to schedule a queue for perp devices
and leave the non-threaded iomapped irq.

At this point I think it may be wise to leave the m_can code alone as it is working and stable and just work on the TCAN driver as
a standalone driver.  A framework would be nice but I think it would destablize the m_can driver which is embedded in many SoC's and
we cannot possibly test everyone of them.

What are your thoughts?

Dan

> Wolfgang.
> 


-- 
------------------
Dan Murphy