[U-Boot] [PATCH] power: regulator: Return success on attempt to disable an always-on regulator

[Lokesh Vutla]

Hi Simon,

On 28/12/18 3:57 AM, Simon Glass wrote:
> Hi Lokesh,
> 
> On Mon, 24 Dec 2018 at 04:08, Lokesh Vutla <lokeshvutla at ti.com> wrote:
>>
>> commit 4f86a724e82c0 ("power: regulator: denied disable on always-on
>> regulator") throws an error when requested to disable an always-on
>> regulator. It is right that an always-on regulator should not be
>> attempted to be disabled. But at the same time regulator framework
>> should not return an error when such request is received. Instead
>> it should just return success without attempting to disable the
>> specified regulator. This is because the requesting driver will
>> not have the idea if the regulator is always-on or not. The
>> requesting driver will always try to enable/disable regulator as
>> per the required flow. So it is upto regulator framework to not
>> break such scenarios.
> 
> Can the caller not check the error code? It is -EACCES in this case.

We considered this an one of the option but I ended up fixing regulator 
framework due to the following reasons:
- If regulator framework returns -EACCES on this scenario then:
	- -EACCES should be checked in all the existing usage of the api[1] or else 
someone else might encounter the same problem.
	- Any future usage of the api should take of handling this error.
	- From a client driver perspective it is not really an error. It is doing the 
right thing and receiving an error might be confusing.

Hope this is clear. Also just to add one more point, I adapted this error 
handling from Linux kernel[2].

[1] ➜  u-boot git:(master) git grep -in "regulator_set_enable(.*, false)"
cmd/regulator.c:410:    ret = regulator_set_enable(dev, false);
drivers/mmc/mmc.c:2552:     int ret = regulator_set_enable(mmc->vmmc_supply, false);
drivers/mmc/omap_hsmmc.c:473:   ret = regulator_set_enable(priv->pbias_supply, 
false);
drivers/mmc/omap_hsmmc.c:478:   ret = regulator_set_enable(mmc->vqmmc_supply, 
false);
drivers/net/fec_mxc.c:1414:     regulator_set_enable(priv->phy_supply, false);
drivers/phy/meson-gxl-usb2.c:174:       int ret = 
regulator_set_enable(priv->phy_supply, false);
drivers/phy/phy-rcar-gen3.c:101:    return 
regulator_set_enable(priv->vbus_supply, false);
drivers/phy/phy-stm32-usbphyc.c:251:        ret = 
regulator_set_enable(usbphyc_phy->vdda1v1, false);
drivers/phy/phy-stm32-usbphyc.c:257:        ret = 
regulator_set_enable(usbphyc_phy->vdda1v8, false);
drivers/phy/phy-stm32-usbphyc.c:263:        ret = 
regulator_set_enable(usbphyc_phy->vdd, false);
drivers/usb/host/dwc2.c:199:        ret = 
regulator_set_enable(priv->vbus_supply, false);
drivers/usb/host/ehci-generic.c:60:     return 
regulator_set_enable(priv->vbus_supply, false);
drivers/usb/host/xhci-rockchip.c:161:       ret = 
regulator_set_enable(plat->vbus_supply, false);
drivers/video/pwm_backlight.c:160:          ret = 
regulator_set_enable(priv->reg, false);
test/dm/adc.c:74:   ut_assertok(regulator_set_enable(supply, false));

[2]  [1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/regulator/core.c#n2333

Thanks and regards,
Lokesh