linux-kernel - Re: [PATCH v3 1/13] mmc: sunxi: Fix clock frequency change sequence

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Date:   Wed, 25 Jan 2017 09:26:02 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Andre Przywara <andre.przywara@....com>
Subject: Re: [PATCH v3 1/13] mmc: sunxi: Fix clock frequency change sequence

Hi Ulf,

On Tue, Jan 24, 2017 at 09:12:07AM +0100, Ulf Hansson wrote:
> On 16 January 2017 at 17:56, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
> > The MMC and SD specifications documents that the clock frequency should
> > only be changed once gated.
> 
> Where?
> 
> >
> > The current code first modifies the parent clock, gates it and then
> > modifies the internal divider. This means that since the parent clock rate
> > might be changed, the bus clock might be changed as well before it is
> > gated, which breaks the specification.
> >
> > Move the gating before the parent rate modification.
> 
> This all makes perfect sense to me, however I am not sure you need to
> refer to the spec to justify these changes.

I can't find it anymore :/

I'll resend that patch reworking the commit log.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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