Re: [RFC PATCH] clk: sunxi-ng: sun4i: Use CLK_SET_RATE_PARENT for mmc2 clock

From: Priit Laes <plaes@plaes.org>
To: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Chen-Yu Tsai <wens@csie.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Jernej Skrabec <jernej.skrabec@siol.net>
Subject: Re: [RFC PATCH] clk: sunxi-ng: sun4i: Use CLK_SET_RATE_PARENT for mmc2 clock
Date: Mon, 11 Feb 2019 14:35:52 +0000	[thread overview]
Message-ID: <20190211143552.2uqx6yy53dyv5lbl@plaes.org> (raw)
In-Reply-To: <20190206155227.wbkzvsdgykir4wn5@flea>

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

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