linux-kernel - Re: [PATCH RESEND 06/16] mfd: add TI LMU driver

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Date:	Tue, 24 Nov 2015 15:39:35 +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 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.

Best regards,
Milo
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