linux-kernel - Re: [RFC PATCH] clk: sunxi-ng: sun4i: Use CLK_SET_RATE

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Message-ID: <20190211153402.s5qij5idvhbtsw2y@flea>
Date:   Mon, 11 Feb 2019 16:34:02 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Priit Laes <plaes@...es.org>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>
Subject: Re: [RFC PATCH] clk: sunxi-ng: sun4i: Use CLK_SET_RATE_PARENT for
 mmc2 clock

On Mon, Feb 11, 2019 at 02:35:52PM +0000, Priit Laes wrote:
> On Wed, Feb 06, 2019 at 04:52:27PM +0100, Maxime Ripard wrote:
> > Hi,
> > 
> > On Wed, Feb 06, 2019 at 10:03:09AM +0000, Priit Laes wrote:
> > > > > I'm concerned for other users of the PLL-PERIPH clock. AFAIK
> > > > > all of them, except the HRTIMER, expect the clock rate to stay
> > > > > the same and not change underneath them. And SATA expects it to
> > > > > be at 600 MHz, as the datasheet says. And while it may not directly
> > > > > apply to the LIME2, eMMC on newer SoCs / boards run at the slightly
> > > > > reduced rate of 50 MHz just fine.
> > > > > 
> > > > > In the commit in question, clocks without CLK_SET_RATE_PARENT
> > > > > should be using the old code (now in the if conditional block),
> > > > > i.e. the behavior should not have changed.
> > > > > 
> > > > > I don't think this actually "fixes" whatever bug was introduced,
> > > > > but only papers over the issue, and possible introduces further
> > > > > issues for other users.
> > > > 
> > > > You're right, I've overlooked that it was pll-periph being
> > > > affected. I've dropped it for now.
> > > 
> > > Any ideas what could be done. I currently have no time to debug it,
> > > but it affects existing systems.
> > 
> > I can't find what would change with that commit either if the flag
> > isn't set, so looking at the register state before and after that
> > commit would help I guess?
> 
> Register dump without the patch:
> 
> $ busybox devmem 0x01c20090
> 0x0250030E
> 
> pll-ddr-base     2 2 0   768000000          0     0  50000
>    pll-ddr-other 1 1 0   768000000          0     0  50000
>       mmc2       3 3 0    51200000          0     0  50000
> 
> Register dump with patch applied, booted from mmc0 and after mounting emmc:
> 
> $ busybox devmem 0x01c20090
> 0x8140020B
> 
> pll-periph-base  3 3 0  1200000000          0     0  50000
>    pll-periph    6 6 0   600000000          0     0  50000
>       mmc2       3 3 0    50000000          0     0  50000

I meant the whole Clock controller, ideally a diff between the two
states would be great.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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