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From: Mark Brown <broonie@kernel.org>
To: Chen-Yu Tsai <wens@csie.org>
Cc: Lee Jones <lee.jones@linaro.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-sunxi <linux-sunxi@googlegroups.com>
Subject: Re: [PATCH v2 2/2] mfd: axp20x: Fix AXP806 access errors on cold boot
Date: Wed, 14 Dec 2016 17:40:53 +0000	[thread overview]
Message-ID: <20161214174053.qsm6umlgtdivevwt@sirena.org.uk> (raw)
In-Reply-To: <CAGb2v66vggNNfFrAiNKKGXY0ayiG1qh5tcRok2NLTRkVHWKFeg@mail.gmail.com>

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On Wed, Dec 14, 2016 at 09:52:31PM +0800, Chen-Yu Tsai wrote:

> What this patch does is make sure the registers match, to guarantee
> access, and then reinitialize the regmap cache to get rid of any
> stale data.

So what you're saying is that previous writes may have been ignored?

> > If the chip has been reset then you'd want to reset the cache too.  I've
> > no idea if that's needed here or not though, it depends what happens to
> > the global state of the chip when this reconfiguration happens.

> It is not a reset in the general sense. I suppose a better way would
> be to do an explicit write to the register first, then initialize
> the regmap. I'd have to export the write function from the RSB bus
> driver first though.

Surely just doing a write immediately after initializing the regmap
would have the same effect?  That'd ensure that the hardware has the
desired value before there are any other writes.  But I might be missing
something here.

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From: broonie@kernel.org (Mark Brown)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 2/2] mfd: axp20x: Fix AXP806 access errors on cold boot
Date: Wed, 14 Dec 2016 17:40:53 +0000	[thread overview]
Message-ID: <20161214174053.qsm6umlgtdivevwt@sirena.org.uk> (raw)
In-Reply-To: <CAGb2v66vggNNfFrAiNKKGXY0ayiG1qh5tcRok2NLTRkVHWKFeg@mail.gmail.com>

On Wed, Dec 14, 2016 at 09:52:31PM +0800, Chen-Yu Tsai wrote:

> What this patch does is make sure the registers match, to guarantee
> access, and then reinitialize the regmap cache to get rid of any
> stale data.

So what you're saying is that previous writes may have been ignored?

> > If the chip has been reset then you'd want to reset the cache too.  I've
> > no idea if that's needed here or not though, it depends what happens to
> > the global state of the chip when this reconfiguration happens.

> It is not a reset in the general sense. I suppose a better way would
> be to do an explicit write to the register first, then initialize
> the regmap. I'd have to export the write function from the RSB bus
> driver first though.

Surely just doing a write immediately after initializing the regmap
would have the same effect?  That'd ensure that the hardware has the
desired value before there are any other writes.  But I might be missing
something here.
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  reply	other threads:[~2016-12-14 17:41 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-23  3:16 [PATCH v2 0/2] mfd: axp20x: Fix AXP806 access errors on cold boot Chen-Yu Tsai
2016-11-23  3:16 ` Chen-Yu Tsai
2016-11-23  3:16 ` [PATCH v2 1/2] mfd: axp20x: Add address extension registers for AXP806 regmap Chen-Yu Tsai
2016-11-23  3:16   ` Chen-Yu Tsai
2016-12-09 11:05   ` Lee Jones
2016-12-09 11:05     ` Lee Jones
2016-11-23  3:16 ` [PATCH v2 2/2] mfd: axp20x: Fix AXP806 access errors on cold boot Chen-Yu Tsai
2016-11-23  3:16   ` Chen-Yu Tsai
2016-12-09 11:20   ` Lee Jones
2016-12-09 11:20     ` Lee Jones
2016-12-13 16:47     ` Mark Brown
2016-12-13 16:47       ` Mark Brown
2016-12-14 13:52       ` Chen-Yu Tsai
2016-12-14 13:52         ` Chen-Yu Tsai
2016-12-14 17:40         ` Mark Brown [this message]
2016-12-14 17:40           ` Mark Brown
2017-01-03  3:54           ` Chen-Yu Tsai
2017-01-03  3:54             ` Chen-Yu Tsai

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