Message-ID: <56556D01.9070804@ti.com>
Date:	Wed, 25 Nov 2015 17:10:41 +0900
From:	"Kim, Milo" <milo.kim@...com>
To:	Lee Jones <lee.jones@...aro.org>
CC:	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Jingoo Han <jingoohan1@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Jean Delvare <jdelvare@...e.com>,
	Jacek Anaszewski <j.anaszewski@...sung.com>,
	Mark Brown <broonie@...nel.org>, <lm-sensors@...sensors.org>,
	<linux-leds@...r.kernel.org>
Subject: Re: [PATCH RESEND 06/16] mfd: add TI LMU driver

On 11/24/2015 5:18 PM, Lee Jones wrote:
> On Tue, 24 Nov 2015, Kim, Milo wrote:
>
>> On 11/24/2015 11:35 AM, Kim, Milo wrote:
>>> Hi Lee,
>>>
>>> Thanks for all your comments. Please see my comments below.
>>>
>>> On 11/23/2015 7:30 PM, Lee Jones wrote:
>>>>> +int ti_lmu_read_byte(struct ti_lmu *lmu, u8 reg, u8 *read)
>>>>>> +{
>>>>>> +	int ret;
>>>>>> +	unsigned int val;
>>>>>> +
>>>>>> +	ret = regmap_read(lmu->regmap, reg, &val);
>>>>>> +	if (ret < 0)
>>>>>> +		return ret;
>>>>>> +
>>>>>> +	*read = (u8)val;
>>>>>> +	return 0;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(ti_lmu_read_byte);
>>>> It doesn't get much more simple than this.
>>>>
>>>> What's the purpose of abstracting it?
>>>>
>>>>>> +int ti_lmu_write_byte(struct ti_lmu *lmu, u8 reg, u8 data)
>>>>>> +{
>>>>>> +	return regmap_write(lmu->regmap, reg, data);
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(ti_lmu_write_byte);
>>>>>> +
>>>>>> +int ti_lmu_update_bits(struct ti_lmu *lmu, u8 reg, u8 mask, u8 data)
>>>>>> +{
>>>>>> +	return regmap_update_bits(lmu->regmap, reg, mask, data);
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(ti_lmu_update_bits);
>>>> Okay, I lied, it does get more simple.
>>>>
>>>> Seems like abstraction for the sake of abstraction here.
>>>>
>>>> Feel free to try and convince me otherwise.
>>>>
>>>
>>> The main reason was that LMU MFD core provides consistent register
>>> access among LMU drivers like ti-lmu-backlight, leds-lm3633,
>>> lm363x-regulator and ti-lmu-fault-monitor('ti-lmu-hwmon' will be changed
>>> to this in the 2nd patch).
>>>
>>> However, LMU register helpers are exactly same as regmap interface
>>> except using ti_lmu data structure. So let me replace them with regmap
>>> functions. Thanks for pointing this out.
>>
>> I just realized LMU MFD core helpers also provide module
>> dependencies by using EXPORT_SYMBOL_GPL().
>>
>> # modprobe -D ti-lmu-backlight
>> insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
>> insmod /lib/modules/<ver>/kernel/drivers/video/backlight/ti-lmu-backlight.ko
>> # modprobe -D ti-lmu-fault-monitor
>> insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu-fault-monitor.ko
>> # modprobe -D lm363x-regulator
>> insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
>> insmod /lib/modules/<ver>/kernel/drivers/regulator/lm363x-regulator.ko
>> # modprobe -D leds-lm3633
>> insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
>> insmod /lib/modules/<ver>/kernel/drivers/leds/leds-lm3633.ko
>>
>> ti-lmu.ko should be loaded first because it has hardware enable pin
>> control code. Four other drivers have dependency on this module.
>> Without EXPORT_SYMBOL_GPL(), this dependency will be gone like
>> below.
>>
>> # modprobe -D ti-lmu-backlight
>> insmod /lib/modules/<ver>/kernel/drivers/video/backlight/ti-lmu-backlight.ko
>> # modprobe -D ti-lmu-fault-monitor
>> insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu-fault-monitor.ko
>> # modprobe -D lm363x-regulator
>> insmod /lib/modules/<ver>/kernel/drivers/regulator/lm363x-regulator.ko
>> # modprobe -D leds-lm3633
>> insmod /lib/modules/<ver>/kernel/drivers/leds/leds-lm3633.ko
>>
>> If LMU MFD core module is not loaded and other modules call regmap
>> helpers, then loaded drivers will not work because hardware is not
>> enabled yet.
>>
>> So I'd like to keep LMU MFD helpers for module dependencies.
>> Additionally, I'll modify 'ti_lmu_read_byte()' as follows.
>>
>> int ti_lmu_read_byte(struct ti_lmu *lmu, u8 reg, u8 *read)
>> {
>> 	return regmap_read(lmu->regmap, reg, (unsigned int *)read);
>> }
>> EXPORT_SYMBOL_GPL(ti_lmu_read_byte);
>>
>> Please let me know if you have better idea.
>
> You're keeping the helpers for the wrong reasons.  This has now become
> a hack.  If you have dependencies between modules, either use the init
> levels or defer probe in the usual way.
>

Yes, I was wrong. In case LMU MFD core is not loaded, other LMU modules 
like ti-lmu-backlight isn't probed because no platform device (mfd 
device) exists. So the situation which I've mentioned never happens.
And if GPIO controller is not ready and HW enable GPIO request gets 
failed on LMU MFD initialization, this will be processed later because 
it returns as error code '-EPROBE_DEFER' from GPIO subsystem. In other 
words, there is no dependency issue between LMU modules. Those are just 
platform device and driver.

OK, I'll remove LMU register helpers in the 2nd patch. Then, each LMU 
driver will call regmap helpers directly.
Thanks for your comments.

Best regards,
Milo
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