linux-kernel - Re: [PATCH] drm/panel: lvds: Handle the optional regulator case properly

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Date:   Fri, 12 Jan 2018 00:09:39 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: lvds: Handle the optional regulator case properly

Hi Maxime,

On Friday, 12 January 2018 00:06:06 EET Laurent Pinchart wrote:
> On Thursday, 11 January 2018 15:12:56 EET Maxime Ripard wrote:
> > On Thu, Jan 11, 2018 at 03:05:01PM +0200, Laurent Pinchart wrote:
> >> On Wednesday, 10 January 2018 17:59:41 EET Maxime Ripard wrote:
> >>> The devm_regulator_get_optional function, unlike it was assumed in the
> >>> commit a1c55bccf600 ("drm/panel: lvds: Add support for the power-supply
> >>> property"), is actually returning an error pointer with -ENODEV instead
> >>> of NULL when there's no regulator to find.
> >>> 
> >>> Make sure we handle that case properly.
> >>> 
> >>> Fixes: a1c55bccf600 ("drm/panel: lvds: Add support for the power-supply
> >>> property") Signed-off-by: Maxime Ripard
> >>> <maxime.ripard@...e-electrons.com>
> >>> ---
> >>> 
> >>>  drivers/gpu/drm/panel/panel-lvds.c | 9 +++++++--
> >>>  1 file changed, 7 insertions(+), 2 deletions(-)
> >>> 
> >>> diff --git a/drivers/gpu/drm/panel/panel-lvds.c
> >>> b/drivers/gpu/drm/panel/panel-lvds.c index 57e38a9e7ab4..9f46e7095c0e
> >>> 100644
> >>> --- a/drivers/gpu/drm/panel/panel-lvds.c
> >>> +++ b/drivers/gpu/drm/panel/panel-lvds.c
> >>> @@ -215,8 +215,13 @@ static int panel_lvds_probe(struct platform_device
> >>> *pdev)
> >>> 	lvds->supply = devm_regulator_get_optional(lvds->dev, "power");
> >>>  	if (IS_ERR(lvds->supply)) {
> >>>  		ret = PTR_ERR(lvds->supply);
> >>> -		dev_err(lvds->dev, "failed to request regulator: %d\n", ret);
> >>> -		return ret;
> >>> +
> >>> +		if (ret != -ENODEV) {
> >>> +			dev_err(lvds->dev, "failed to request regulator: %d\n", ret);
> >>> +			return ret;
> >> 
> >> I wouldn't print an error message if ret == -EPROBE_DEFER.
> >> 
> >>> +		} else {
> >>> +			lvds->supply = NULL;
> >>> +		}
> >>>  	}
> >> 
> >> How about
> >> 
> >> 	lvds->supply = devm_regulator_get_optional(lvds->dev, "power");
> >> 	if (IS_ERR(lvds->supply)) {
> >> 		ret = PTR_ERR(lvds->supply);
> >> 		if (ret != -ENODEV) {
> >> 			if (ret == -EPROBE_DEFER)
> > 
> > I guess that would be != -EPROBE_DEFER
> 
> Of course, my bad.
> 
> >> 				dev_err(lvds->dev, "failed to request regulator: %d\n", ret);
> >> 			return ret;
> >> 		}
> >> 		
> >> 		lvds->supply = NULL;
> >> 	}
> > 
> > Otherwise, it works for me.

With the above change,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> >> My preference, however, would be for devm_regulator_get_optional() to
> >> return NULL when no regulator is present. The current implementation
> >> returns -ENODEV in multiple cases, making it impossible to properly
> >> discriminate between having no regulator and not being able to get the
> >> regulator due to an error.
> > 
> > It would feel more intuitive to me too, but it would also require to
> > fix most of the call sites that would have a similar pattern.
> 
> Of course. I don't mean we need to delay this patch, but I still think it
> would be a good API improvement that could be developed separately (and of
> course I wouldn't complain if you volunteered ;-)).

-- 
Regards,

Laurent Pinchart