linux-kernel - Re: [PATCH v2 1/3] drivers/mfd/menf21bmc: introduce MEN 14F021P00 BMC MFD Core driver

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Date:	Wed, 28 May 2014 06:29:45 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Andreas Werner <andreas.werner@....de>,
	Lee Jones <lee.jones@...aro.org>
CC:	Johannes Thumshirn <johannes.thumshirn@....de>,
	linux-kernel@...r.kernel.org, sameo@...ux.intel.com, wim@...ana.be,
	linux-watchdog@...r.kernel.org, cooloney@...il.com,
	rpurdie@...ys.net, linux-leds@...r.kernel.org
Subject: Re: [PATCH v2 1/3] drivers/mfd/menf21bmc: introduce MEN 14F021P00
 BMC MFD Core driver

On 05/28/2014 04:51 AM, Andreas Werner wrote:
> aOn Wed, May 28, 2014 at 09:24:05AM +0100, Lee Jones wrote:
>>>>> The MEN 14F021P00 Board Management Controller provides an
>>>>> I2C interface to the host to access the feature implemented in the BMC.
>>>>> The BMC is a PIC Microntroller assembled on CPCI Card from MEN Mikroelektronik
>>>>> and on a few Box/Display Computer.
>>>>>
>>>>> Added MFD Core driver, supporting the I2C communication to the device.
>>>>>
>>>>> The MFD driver currently supports the following features:
>>>>> 	- Watchdog
>>>>> 	- LEDs
>>>>>
>>>>> Signed-off-by: Andreas Werner <andreas.werner@....de>
>>>>> ---
>>>>>   drivers/mfd/Kconfig           |  12 +++
>>>>>   drivers/mfd/Makefile          |   1 +
>>>>>   drivers/mfd/menf21bmc.c       | 220 ++++++++++++++++++++++++++++++++++++++++++
>>>>>   include/linux/mfd/menf21bmc.h |  31 ++++++
>>>>>   4 files changed, 264 insertions(+)
>>>>>   create mode 100644 drivers/mfd/menf21bmc.c
>>>>>   create mode 100644 include/linux/mfd/menf21bmc.h
>>
>> [...]
>>
>>>>> +static int menf21bmc_write_byte(struct i2c_client *client, u8 val)
>>>>> +{
>>>>> +	int ret;
>>>>> +	struct menf21bmc *data = i2c_get_clientdata(client);
>>>>> +
>>>>> +	mutex_lock(&data->lock);
>>>>> +	ret = i2c_smbus_write_byte(client, val);
>>>>> +	mutex_unlock(&data->lock);
>>>>> +
>>>>> +	return ret;
>>>>> +}
>>>>
>>>> Didn't we ask you to remove these?  Just make the i2c_smbus_* calls
>>>> from within the driver.  The I2C subsystem conducts its own locking.
>>>> I'm really starting to frown on aggregation for the sake of
>>>> aggregation.  It's just overhead.
>>>>
>>>
>>> Correct me if I'm wrong but as far as I remember Guenther asked to retain the
>>> original API, not the remove the "abstraction layer". Once we build a board with
>>> one of these BMCs attached via e.g. SPI we would have to reintroduce it anyways,
>>> in order to re-use these drivers.
>>
>> If there are two or more possible interfaces then I agree, these
>> aggregations would be the best approach.  However, as it stands, that's
>> not currently the case.
>>
>> Genuine question; are Men on the verge of building such a board, or
>> are we talking about 'ifs' and 'maybes'?
>>
>
> I think it was a missunderstanding. I also thought that i just
> have to adapt the wrapper to the original API, that is what I did in the patch,
> and not to delete the functions completly.
>
> Anayway, we currently have another project which use a STM32 MCR connected to USB.
> A nice feature of this STM is to update the firmware using the USB interface.
> This is easy to implement and fast.
>
> We want to use such a functionality in all of our MCRs to easily update the firmware
> at the customer if we found a bug.
>
> We also plan to have a BMC connected to USB. Then we have i2c and USB.
>

Even more likely that you would have to change the API in that case to be less
I2C centric.

Guenter

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