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    SubjectRe: [PATCH RESEND 06/16] mfd: add TI LMU driver
    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.

    --
    Lee Jones
    Linaro STMicroelectronics Landing Team Lead
    Linaro.org │ Open source software for ARM SoCs
    Follow Linaro: Facebook | Twitter | Blog


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