linux-kernel - Re: [PATCH RFC 1/2] regmap: add option to disable debugfs

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Date:   Wed, 22 Jun 2022 17:27:09 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Dong Aisheng <dongas86@...il.com>
Cc:     Aisheng Dong <aisheng.dong@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        Peng Fan <peng.fan@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>
Subject: Re: [PATCH RFC 1/2] regmap: add option to disable debugfs

On Thu, Jun 23, 2022 at 12:05:46AM +0800, Dong Aisheng wrote:
> On Wed, Jun 22, 2022 at 8:36 PM Mark Brown <broonie@...nel.org> wrote:

> > On Wed, Jun 22, 2022 at 06:12:49PM +0800, Dong Aisheng wrote:
> >
> > > NOTE:  i didn't fix _regmap_write() as i.MX controls regmap write well in driver
> > > with power enabled first, so don't have issues in reality.

> > I can't tell what you think the problem is with _regmap_write()?

> Because from what I see,  _regmap_write() seems still can write to HW
> register even with cache_only mode set theoretically.

Ah, I see - we don't enforce cache_only if bypass is enabled somehow,
but we will complain if you try to enable both at the same time so I'm
not sure that's an issue?

> > > -       WARN_ON(map->cache_bypass && enable);
> > > +//     WARN_ON(map->cache_bypass && enable);

> > What is the purpose of this change?  Why would the combination of cache
> > only and bypass modes work be a good idea, and how should things behave
> > in that case?

> Because without this change, there will be a kernel dump caused by
> WARN_ON when drivers call regcache_cache_only(map, true) after power
> is off. There's no cache used in the imx blkctl driver. So map->cache_bypass
> is default to true.

cache_bypass is only going to be true if something enabled bypass, why
would a device that doesn't use a cache enable bypass?  It does get
turned on transiently by things like patching but those only make sense
if the device can be accessed so caceh_only shouldn't be on then.

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