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

[Maxime Ripard <maxime.ripard@bootlin.com>]

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On Tue, Feb 05, 2019 at 09:44:02PM +0800, Chen-Yu Tsai wrote:
> On Tue, Feb 5, 2019 at 5:45 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> >
> > On Sat, Feb 02, 2019 at 05:52:09PM +0200, Priit Laes wrote:
> > > Recent patch of improving MP clock rate calculations by taking
> > > into account whether adjusting parent rate is allowed, have
> > > unfortunately broken eMMC support on A20 Olinuxino-Lime2-eMMC
> > > boards which fail with following error:
> > >
> > > [snip]
> > > EXT4-fs (mmcblk1p4): INFO: recovery required on readonly filesystem
> > > EXT4-fs (mmcblk1p4): write access will be enabled during recovery
> > > sunxi-mmc 1c11000.mmc: data error, sending stop command
> > > sunxi-mmc 1c11000.mmc: send stop command failed
> > > [/snip]
> > >
> > > Previously, mmc2 clock was requesting 520MHz and settling at 512MHz
> > > clock rate with following parents:
> 
> You mean 52 and 51.2 MHz.
> 
> > > [snip]
> > > pll-ddr-base        2  2        0   768000000 0     0  50000
> > >    pll-ddr-other    1  1        0   768000000 0     0  50000
> > >       mmc2          0  0        0    51200000 0     0  50000
> > > [/snip]
> > >
> > > Now, after the improvements, requested and settled rate are both
> > > 520MHz, but as mmc2 clock cannot adjust parent rate, the situation
> > > ends up like this:
> > > [snip]
> > > 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
> > > [/snip]
> > >
> > > With this patch (allowing mmc2 to set parent rate), we end up with
> > > working tree with both mmc0 (sd-card) and mmc2 (eMMC) working:
> > > [snip]
> > > pll-periph-base     3  3        0   312000000 0     0  50000
> > >    mbus             1  1        0    78000000 0     0  50000
> > >    pll-periph-sata  1  1        0    26000000 0     0  50000
> > >       sata          1  1        0    26000000 0     0  50000
> > >    pll-periph       5  5        0   156000000 0     0  50000
> > >       mmc2          0  0        0    52000000 0     0  50000
> > >       mmc0          0  0        0    39000000 0     0  50000
> > > [/snip]
> > >
> > > Fixes: 3f790433c3cb ("clk: sunxi-ng: Adjust MP clock parent rate when allowed")
> > > Signed-off-by: Priit Laes <plaes@plaes.org>
> >
> > Applied, thanks!
> > Maxime
> 
> 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.

Maxime

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

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