linux-kernel - Re: [PATCH] regulator: core: add regulator_get_linear

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Message-ID: <20130607095936.GK31367@sirena.org.uk>
Date:	Fri, 7 Jun 2013 10:59:36 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Paul Walmsley <pwalmsley@...dia.com>
Cc:	Liam Girdwood <lgirdwood@...il.com>, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, Andrew Chew <achew@...dia.com>,
	Matthew Longnecker <mlongnecker@...dia.com>
Subject: Re: [PATCH] regulator: core: add regulator_get_linear_step()

On Fri, Jun 07, 2013 at 09:38:10AM +0000, Paul Walmsley wrote:

> +static int get_cvb_voltage(struct platform_device *pdev, int c0, int c1,
> +			   int c2)
> +{
> +	struct tegra_dfll *td = dev_get_drvdata(&pdev->dev);
> +	/* apply only speedo scale: output mv = cvb_mv * v_scale */
> +	int mv;
> +
> +	/* combined: apply voltage scale and round to cvb alignment step */
> +	mv = DIV_ROUND_CLOSEST(c2 * td->speedo_value, td->cvb_speedo_scale);
> +	mv = DIV_ROUND_CLOSEST((mv + c1) * td->speedo_value,
> +			       td->cvb_speedo_scale) + c0;
> +
> +	/* XXX Bring back cvb_alignment_uv; put it in the board dfll DT */
> +	return DIV_ROUND_UP(mv * 1000,
> +			    td->cvb_voltage_scale * td->vdd_step) *
> +		td->vdd_step / 1000;
> +}

Hrm, right.  So I guess for this the question is why you need the steps
at all - can't the driver just ask for the voltage it wants with
whatever tolerance is appropriate (or just specify the maximum tolerable
voltage if that's better)?  I'm not sure what cvb_voltage_scale is.

I guess the problem here is that you have to hit some fairly tight
tolerances on the voltage?

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