linux-kernel - RE: [PATCH v2] regulator: ad5398: Fix min/max current limit boundary checking

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Message-ID: <1341315373.3158.3.camel@phoenix>
Date:	Tue, 03 Jul 2012 19:36:13 +0800
From:	Axel Lin <axel.lin@...il.com>
To:	"Zhang, Sonic" <Sonic.Zhang@...log.com>
Cc:	Lars-Peter Clausen <lars@...afoo.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Liam Girdwood <lrg@...com>
Subject: RE: [PATCH v2] regulator: ad5398: Fix min/max current limit
 boundary checking


> >The equation to calculate the selector does not depend on max_uA.
> >So I think we don't need to set the requested max_uA.
> >
> 
> But, ad5398_set_current_limit() behaves different for min_uA and max_uA with you patch. Is this expected?
> 

What we want is to set the smallest current supported by this hardware
within the range you requested.

Current code uses below equation to choose selector:
selector = DIV_ROUND_UP((min_uA - chip->min_uA) * chip->current_level,
                        range_uA);

With this equation, we need to ensure min_uA >= chip->min_uA,
otherwise it returns a negative selector.

That is why we need to add:
if (min_uA < chip->min_uA)
        min_uA = chip->min_uA;


Axel

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