From: Philipp Zabel <p.zabel@pengutronix.de>
To: Guenter Roeck <linux@roeck-us.net>,
Yingjoe Chen <yingjoe.chen@mediatek.com>
Cc: mark.rutland@arm.com, alsa-devel@alsa-project.org,
broonie@kernel.org, yong.liang@mediatek.com,
Jiaxin Yu <jiaxin.yu@mediatek.com>,
lgirdwood@gmail.com, tzungbi@google.com, robh+dt@kernel.org,
linux-mediatek@lists.infradead.org, eason.yen@mediatek.com,
perex@perex.cz, wim@linux-watchdog.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/4] watchdog: mtk_wdt: mt8183: Add reset controller
Date: Tue, 08 Oct 2019 16:08:39 +0200 [thread overview]
Message-ID: <1570543719.18914.7.camel@pengutronix.de> (raw)
In-Reply-To: <70b77fb3-7186-734d-3415-64acb30bab8f@roeck-us.net>
Hi Guenter, Yingjoe,
On Sat, 2019-10-05 at 07:46 -0700, Guenter Roeck wrote:
> On 10/4/19 10:59 PM, Yingjoe Chen wrote:
> > On Thu, 2019-10-03 at 06:49 -0700, Guenter Roeck wrote:
> > > On 9/27/19 3:31 AM, Jiaxin Yu wrote:
> >
> > <snip..>
> >
> >
> > > > +static int toprgu_reset_assert(struct reset_controller_dev *rcdev,
> > > > + unsigned long id)
> > > > +{
> > > > + unsigned int tmp;
> > > > + unsigned long flags;
> > > > + struct toprgu_reset *data = container_of(rcdev,
> > > > + struct toprgu_reset, rcdev);
> > > > +
> > > > + spin_lock_irqsave(&data->lock, flags);
> > > > +
> > > > + tmp = __raw_readl(data->toprgu_swrst_base + data->regofs);
> > > > + tmp |= BIT(id);
> > > > + tmp |= WDT_SWSYS_RST_KEY;
> > > > + writel(tmp, data->toprgu_swrst_base + data->regofs);
> > > > +
> > > > + spin_unlock_irqrestore(&data->lock, flags);
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +static int toprgu_reset_deassert(struct reset_controller_dev *rcdev,
> > > > + unsigned long id)
> > > > +{
> > > > + unsigned int tmp;
> > > > + unsigned long flags;
> > > > + struct toprgu_reset *data = container_of(rcdev,
> > > > + struct toprgu_reset, rcdev);
> > > > +
> > > > + spin_lock_irqsave(&data->lock, flags);
> > > > +
> > > > + tmp = __raw_readl(data->toprgu_swrst_base + data->regofs);
> > > > + tmp &= ~BIT(id);
> > > > + tmp |= WDT_SWSYS_RST_KEY;
> > > > + writel(tmp, data->toprgu_swrst_base + data->regofs);
> > > > +
> > > > + spin_unlock_irqrestore(&data->lock, flags);
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +static int toprgu_reset(struct reset_controller_dev *rcdev,
> > > > + unsigned long id)
> > > > +{
> > > > + int ret;
> > > > +
> > > > + ret = toprgu_reset_assert(rcdev, id);
> > > > + if (ret)
> > > > + return ret;
> > > > +
> > > > + return toprgu_reset_deassert(rcdev, id);
> > >
> > > Unless there is additional synchronization elsewhere, parallel calls
> > > to the -> assert, and ->reset callbacks may result in the reset being
> > > deasserted while at least one caller (the one who called the ->assert
> > > function) believes that it is still asserted.
> > >
> > > [ ... and if there _is_ additional synchronization elsewhere, the
> > > local spinlock would be unnecessary ]
> > >
> >
> > I'm not sure if this count as additional synchronization, but you could
> > get exclusive control to the reset by calling
> > reset_control_get_exclusive so others won't try to reset the component
> > while you are using it.
> >
> > In this case, you still need spinlock because other drivers might trying
> > to reset their components and they share same register.
>
> That isn't what I meant. I referred to synchronization in the reset
> controller core. AFAICS the reset controller core prevents parallel
> calls into the same reset controller driver using atomics.
No, it doesn't. The atomics in struct reset_control prevent parallel
calls on the same, reset control only, for shared reset controls.
Two calls on different reset controls can still run simultaneously on
the same rcdev.
> Unfortunately, it is not well defined if additional synchronization on
> driver level is needed - some drivers implement it, some drivers
> don't,
I think all drivers protect read/modify/write cycles to shared registers
with a spinlock. Those that don't either have separate set/clear
registers or use regmap, otherwise it might be a bug.
> and I don't find a documentation.
I am aware this is a problem.
regards
Philipp
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-10-08 14:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-27 10:31 [PATCH v2 0/4] ASoC: mt8183: fix audio playback slowly after playback Jiaxin Yu
2019-09-27 10:31 ` [PATCH v2 1/4] dt-bindings: mediatek: mt8183: Add #reset-cells Jiaxin Yu
2019-09-27 10:31 ` [PATCH v2 2/4] watchdog: mtk_wdt: mt8183: Add reset controller Jiaxin Yu
2019-09-28 17:49 ` Guenter Roeck
2019-09-30 8:17 ` Yingjoe Chen
2019-10-03 13:49 ` Guenter Roeck
2019-10-05 5:59 ` Yingjoe Chen
2019-10-05 14:46 ` Guenter Roeck
2019-10-08 14:08 ` Philipp Zabel [this message]
2019-10-05 5:50 ` Yingjoe Chen
2019-09-27 10:31 ` [PATCH v2 3/4] dt-bindings: medaitek: mt8183: add property "resets" && "reset-names" Jiaxin Yu
2019-10-08 12:53 ` Applied "dt-bindings: medaitek: mt8183: add property "resets" && "reset-names"" to the asoc tree Mark Brown
2019-09-27 10:31 ` [PATCH v2 4/4] ASoC: mt8183: fix audio playback slowly after playback during bootup Jiaxin Yu
2019-10-05 6:07 ` Yingjoe Chen
2019-10-08 12:11 ` Mark Brown
2019-10-08 12:53 ` Applied "ASoC: mt8183: fix audio playback slowly after playback during bootup" to the asoc tree Mark Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1570543719.18914.7.camel@pengutronix.de \
--to=p.zabel@pengutronix.de \
--cc=alsa-devel@alsa-project.org \
--cc=broonie@kernel.org \
--cc=eason.yen@mediatek.com \
--cc=jiaxin.yu@mediatek.com \
--cc=lgirdwood@gmail.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-mediatek@lists.infradead.org \
--cc=linux@roeck-us.net \
--cc=mark.rutland@arm.com \
--cc=perex@perex.cz \
--cc=robh+dt@kernel.org \
--cc=tzungbi@google.com \
--cc=wim@linux-watchdog.org \
--cc=yingjoe.chen@mediatek.com \
--cc=yong.liang@mediatek.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).