Re: [EXT] Re: [PATCH v9 2/4] irqchip: Add IMX MU MSI controller driver

Marc Zyngier
2022-09-08T14:51:33Z

On Thu, 08 Sep 2022 15:23:53 +0100,
Frank Li <frank.li@nxp.com> wrote:
>
> >
> > On Wed, 07 Sep 2022 04:48:54 +0100,
> > Frank Li <Frank.Li@nxp.com> wrote:
> > >
> > > The MU block found in a number of Freescale/NXP SoCs supports
> > generating
> > > IRQs by writing data to a register
> > >
> > > This enables the MU block to be used as a MSI controller, by leveraging
> > > the platform-MSI API
> >
> > Missing full stop after each sentence.
>
> [Frank Li] Do you means missed "."?

Yes.

> > > diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> > > index 5e4e50122777d..e04c6521dce55 100644
> > > --- a/drivers/irqchip/Kconfig
> > > +++ b/drivers/irqchip/Kconfig
> > > @@ -470,6 +470,15 @@ config IMX_INTMUX
> > > help
> > > Support for the i.MX INTMUX interrupt multiplexer.
> > >
> > > +config IMX_MU_MSI
> > > + bool "i.MX MU work as MSI controller"
> >
> > Why bool? Doesn't it also work as a module?
>
> [Frank Li] I remember you said that irq-chip can't be removed.
> So I am not sure why need build as module.

Not being removed doesn't mean it cannot be built as a module and
loaded on demand. Why should I be forced to have this driver built-in
if my kernel is used on a variety of systems, only one of them having
this device?

> > > +
> > > +struct imx_mu_msi {
> > > + spinlock_t lock;
> > > + raw_spinlock_t reglock;
> >
> > Why two locks? Isn't one enough to protect both MSI allocation (which
> > happens once in a blue moon) and register access?
>
> [Frank Li] Previously your comment, ask me to use raw_spinlock for
> read\write register access. I don't think raw_spinlock is good for
> MSI allocation.

Why wouldn't it be good enough? I'd really like to know.

>
> >
> > Also, where are these locks initialised?
> >
>
> [Frank Li] struct imx_mu_msi is fill zero when allocated.
> Does it still need additional initialization for spinlock?

Have you heard of lockdep? Or CONFIG_DEBUG_SPINLOCK? Maybe you should
try it.

> > > + if (!pdev)
> > > + return -ENODEV;
> >
> > How can that happen?
> >
> [Frank Li] Not sure, many driver check as it.

And? Just because someone does something pointless, you have to
imitate them?

M.

--
Without deviation from the norm, progress is not possible.