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From: Mark Brown <broonie@kernel.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Doug Anderson <dianders@chromium.org>,
	Heiko Stuebner <heiko@sntech.de>,
	Jaehoon Chung <jh80.chung@samsung.com>,
	Seungwon Jeon <tgih.jun@samsung.com>,
	Alexandru Stan <amstan@chromium.org>,
	Alim Akhtar <alim.akhtar@samsung.com>,
	Sonny Rao <sonnyrao@chromium.org>,
	Andrew Bresticker <abrestic@chromium.org>,
	Addy Ke <addy.ke@rock-chips.com>,
	Javier Martinez Canillas <javier.martinez@collabora.co.uk>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	Chris Ball <chris@printf.net>,
	Johan Rudholm <johan.rudholm@axis.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Tim Kryger <tim.kryger@gmail.com>,
	Andrew Gabbasov <andrew_gabbasov@mentor.com>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	linux-mmc <linux-mmc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 2/4] mmc: core: Add mmc_regulator_set_vqmmc()
Date: Fri, 20 Mar 2015 11:28:28 +0000	[thread overview]
Message-ID: <20150320112828.GF2869@sirena.org.uk> (raw)
In-Reply-To: <CAPDyKFroe9N3j9oMWKknH5huv7j8fkrBr5UKjjp190hkqNsNRg@mail.gmail.com>

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On Fri, Mar 20, 2015 at 11:55:50AM +0100, Ulf Hansson wrote:
> On 19 March 2015 at 12:36, Mark Brown <broonie@kernel.org> wrote:

> > The implementation *should* do that anyway, it's just not trivial to
> > implement in an efficient fashion with the current information we have
> > from drivers.

> The APIs regulator_count_voltages() and regulator_list_voltage(), are
> currently used from the mmc core to find out which voltages that is
> supported (with 0.1V granularity). Then that information can be used
> when trying to set a new voltage.

> But I guess such a wrapper API is out of the question?

> Anyway, I get the feeling that we will need to do the same for this case.

As previously discussed the problem is that there can be a *lot* of
voltages on a modern regulator with fine grained voltage steps and
tolerances are also used for things like cpufreq where we care about
performance.  We need something that doesn't require a linear scan of
possible values.

> >> would be good to allow both upper and lower limits to be zero.

> > The lower limit can be zero already though it isn't clear to me that
> > this is useful.  Setting an upper limit of zero seems nonsensical, an
> > upper limit that is lower than the lower limit isn't terribly obvious
> > and removing the upper limit isn't safe - it means that we'll happily
> > oversupply things which is a road to physical damage.

> I am not sure I follow here. In the regulator_set_voltage_tol() you
> can only specifiy one limit (tolerance?). What Dough proposed was to
> add a new API which can have both a low tolerance value and a high
> tolerance value.

Tolerances are not limits - when you say "limit" that sounds like a hard
value.  I can't see any reason why the code would prevent anyone setting
a tolerance of zero, though it should be rare that this is actually the
best thing to do.

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  reply	other threads:[~2015-03-20 11:29 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-11 22:15 [PATCH v4 1/4] mmc: dw_mmc: Don't try to enable the CD until we're sure we're not deferring Doug Anderson
2015-03-11 22:15 ` [PATCH v4 2/4] mmc: core: Add mmc_regulator_set_vqmmc() Doug Anderson
2015-03-16 14:05   ` Ulf Hansson
2015-03-16 15:12     ` Doug Anderson
2015-03-17 10:23       ` Ulf Hansson
2015-03-17 10:38         ` Mark Brown
2015-03-17 11:28           ` Ulf Hansson
2015-03-19  4:09         ` Doug Anderson
2015-03-19 11:14           ` Ulf Hansson
2015-03-19 11:36             ` Mark Brown
2015-03-20 10:55               ` Ulf Hansson
2015-03-20 11:28                 ` Mark Brown [this message]
2015-04-07 20:05                   ` Doug Anderson
2015-04-08 11:28                     ` Mark Brown
2015-03-11 22:15 ` [PATCH v4 3/4] mmc: dw_mmc: Use mmc_regulator_set_vqmmc in start_signal_voltage_switch Doug Anderson
2015-03-11 22:15 ` [PATCH v4 4/4] ARM: dts: Specify VMMC and VQMMC on rk3288-evb Doug Anderson
2015-03-11 23:30   ` Heiko Stuebner
2015-04-07 21:37     ` Heiko Stübner
2015-03-13 11:32 ` [PATCH v4 1/4] mmc: dw_mmc: Don't try to enable the CD until we're sure we're not deferring Jaehoon Chung
2015-03-13 12:10   ` Heiko Stuebner
2015-03-16  2:09     ` Jaehoon Chung
2015-03-27  5:55 ` Jaehoon Chung
2015-03-27 15:46   ` Doug Anderson

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