linux-kernel - Re: [PATCH 08/11] mfd: wm5110: Update to use maple tree register cache

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Message-ID: <20230718170035.GH103419@ediswmail.ad.cirrus.com>
Date:   Tue, 18 Jul 2023 17:00:35 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Mark Brown <broonie@...nel.org>
CC:     Richard Fitzgerald <rf@...nsource.cirrus.com>,
        Lee Jones <lee@...nel.org>, <alsa-devel@...a-project.org>,
        <patches@...nsource.cirrus.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/11] mfd: wm5110: Update to use maple tree register
 cache

On Tue, Jul 18, 2023 at 03:42:00PM +0000, Charles Keepax wrote:
> On Thu, Jul 13, 2023 at 01:49:26AM +0100, Mark Brown wrote:
> > The maple tree register cache is based on a much more modern data structure
> > than the rbtree cache and makes optimisation choices which are probably
> > more appropriate for modern systems than those made by the rbtree cache. In
> > v6.5 it has also acquired the ability to generate multi-register writes in
> > sync operations, bringing performance up to parity with the rbtree cache
> > there.
> > 
> > Update the wm5110 driver to use the more modern data structure.
> > 
> > Signed-off-by: Mark Brown <broonie@...nel.org>
> > ---
> >  drivers/mfd/wm5110-tables.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mfd/wm5110-tables.c b/drivers/mfd/wm5110-tables.c
> > index 65b9b1d6daec..eba324875afd 100644
> > --- a/drivers/mfd/wm5110-tables.c
> > +++ b/drivers/mfd/wm5110-tables.c
> > @@ -3218,7 +3218,7 @@ const struct regmap_config wm5110_i2c_regmap = {
> >  	.readable_reg = wm5110_readable_register,
> >  	.volatile_reg = wm5110_volatile_register,
> >  
> > -	.cache_type = REGCACHE_RBTREE,
> > +	.cache_type = REGCACHE_MAPLE,
> >  	.reg_defaults = wm5110_reg_default,
> >  	.num_reg_defaults = ARRAY_SIZE(wm5110_reg_default),
> >  };
> > 
> > -- 
> > 2.39.2
> > 
> 
> This one appears to cause me some issues, seems to get the IRQs
> into a weird state when doing compressed stream stuff. The
> issue seems to also require commit bfa0b38c1483 ("regmap:
> maple: Implement block sync for the maple tree cache") to be
> present. So it definitely seems to relate to the cache sync,
> but not sure if it is something todo with the device itself,
> or the maple tree stuff yet.
> 

Ah... I think I see the regcache_sync sets async=true, but then
the maple tree code immediately deletes the buffer after calling
_regmap_raw_write. So its a racy use after free.

How would we feel about having the maple tree code, clear async
again?

Thanks,
Charles