On Tue, Oct 01, 2013 at 02:59:43PM -0600, Stephen Warren wrote: > On 10/01/2013 02:53 PM, Thierry Reding wrote: > > On Tue, Oct 01, 2013 at 12:43:57PM -0600, Stephen Warren wrote: > >> On 09/23/2013 03:41 PM, Thierry Reding wrote: > >>> Many backlights require a power supply to work properly. This > >>> commit uses a power-supply regulator, if available, to power up > >>> and power down the panel. > >> > >> I think that all backlights require a power supply, albeit the > >> supply may not be SW-controllable. Hence, shouldn't the regulator > >> be mandatory in the binding, yet the driver be defensively coded > >> such that if one isn't specified, the driver continues to work? > > > > That has already changed in my local version of this patch. > > > >>> diff --git a/drivers/video/backlight/pwm_bl.c > >>> b/drivers/video/backlight/pwm_bl.c > >> > >>> @@ -253,6 +264,16 @@ static int pwm_backlight_probe(struct > >>> platform_device *pdev) } } > >>> > >>> + pb->power_supply = devm_regulator_get_optional(&pdev->dev, > >>> "power"); > >> > >> ... so I think that should be devm_regulator_get(), since the > >> regulator isn't really optional. > >> > >>> + if (IS_ERR(pb->power_supply)) { + if > >>> (PTR_ERR(pb->power_supply) != -ENODEV) { + ret = > >>> PTR_ERR(pb->power_supply); + goto err_gpio; + } + + > >>> pb->power_supply = NULL; > >> > >> If devm_regulator_get_optional() returns an error value or a > >> valid value, then I don't think that this driver should transmute > >> error values into NULL; NULL might be a perfectly valid regulator > >> value. Related, I think the if (pb->power_supply) tests should be > >> replaced with if (!IS_ERR(pb->power_supply)) instead. > > > > All of that is already done in my local tree. This actually turns > > out to work rather smoothly with the new support for optional > > regulators. The regulator core will give you a dummy regulator > > (assuming it's there physically but hasn't been wired up in > > software) that's always on, so the driver doesn't even have to > > special case it anymore. > > OK, hopefully it (the regulator core) complains about the missing DT > property though; I assume you're using regulator_get() not > regulator_get_optional(), since the supply really is not optional. It doesn't always. There's a pr_warn() in _regulator_get(), but that's only for non-DT (since for DT, has_full_constraints is set to true in regulator_init_complete()). Actually that would mean that the regulator core will complain as long as init isn't complete. But since, like many other drivers, pwm-backlight could use deferred probing it's likely to end up being probed after init. Cc'ing Mark Brown. Thierry
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