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
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