linux-kernel - Re: [RESEND PATCH v4 4/4] drm: bridge: anx78xx: Add anx78xx driver support.

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Message-ID: <20160502142215.GA10348@ulmo.ba.sec>
Date:	Mon, 2 May 2016 16:22:15 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, treding@...dia.com,
	airlied@...ux.ie, robh+dt@...nel.org, djkurtz@...omium.org,
	drinkcat@...omium.org, dan.carpenter@...cle.com,
	Emil Velikov <emil.l.velikov@...il.com>,
	Rob Herring <robh@...nel.org>
Subject: Re: [RESEND PATCH v4 4/4] drm: bridge: anx78xx: Add anx78xx driver
 support.

On Mon, May 02, 2016 at 09:54:26AM +0200, Enric Balletbo i Serra wrote:
[...]
> diff --git a/drivers/gpu/drm/bridge/analogix-anx78xx.c b/drivers/gpu/drm/bridge/analogix-anx78xx.c
[...]
> +static int anx78xx_init_pdata(struct anx78xx *anx78xx)
> +{
> +	struct device *dev = &anx78xx->client->dev;
> +	struct anx78xx_platform_data *pdata = &anx78xx->pdata;
> +
> +	/* 1.0V digital core power regulator (optional) */
> +	pdata->dvdd10 = devm_regulator_get(dev, "dvdd10");
> +	if (IS_ERR(pdata->dvdd10)) {
> +		DRM_INFO("DVDD10 regulator not found\n");
> +		pdata->dvdd10 = NULL;
> +	}

I'm almost sure that this isn't what you want. What if the regulator is
hooked up but the bridge driver probes before the regulator. I think
what you really want is to simply propagate the error code via:

	return PTR_ERR(pdata->dvdd10);

My understanding is that the regulator core will give you a dummy one if
there's really nothing hooked up. I think you're also supposed to call
regulator_get_optional() (or the devm_*() equivalent) if this is truly
an optional supply. Given that it's the "core power" regulator I doubt
that it's really optional; it's more likely that you may not be able to
control it, and that it's therefore always on. In that case you're
supposed to model it in DT as a fixed regulator that's always on.

This is fairly minor and it's really the only thing I could find, so no
need to respin just for that. If you're fine with the above solution (to
propagate the error code) I can make the change manually while applying.

Thierry

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