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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>,
        Dan Murphy <dmurphy@ti.com>, <mkl@pengutronix.de>,
        <davem@davemloft.net>
CC:     <linux-can@vger.kernel.org>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
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 <349ef8be-f4c7-25cc-2c33-7ce1fd0b0f40@ti.com>
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 <69d3a046-2d55-06e0-fba7-c9a0d20e6daa@grandegger.com>
From:   "Rizvi, Mohammad Faiz Abbas" <faiz_abbas@ti.com>
Message-ID: <62dd2f40-3ef6-fa6d-dc53-6896b52020ca@ti.com>
Date:   Thu, 10 Jan 2019 13:27:49 +0530
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Hi Dan, Wolfgang,

On 1/10/2019 1:14 PM, Wolfgang Grandegger wrote:
> Hello Dan,
> 
> sorry for my late response on that topic...
> 
> Am 09.01.19 um 21:58 schrieb Dan Murphy:
>> 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.
> 
> Unfortunately, I do not have m_can hardware at hand.

There are exactly 3 platforms in mainline that use the m_can driver. I 
can help Dan test it on a dra76x. I haven't had a chance to look at the 
changes in depth, but just testing for regressions on existing platforms 
shouldn't be too hard once we have it working on one.

Thanks,
Faiz

> 
>> What are your thoughts?
> 
> What we need is a common set of functions doing tx, rx, error and state
> handling. This will requires substantial changes to the existing
> io-mapped m_can driver, of course. I still believe it's worth the
> effort, but I agree that it's difficult for you to re-write and test the
> existing m_can driver.
> 
> What about implementing such a set of common functions plus the SPI
> specific part for your TCAN device. What do you/others think?
> 
> Wolfgang.
>