Re: [PATCH V2 2/2] irqchip/sifive-plic: Add thead,c9xx-plic support

["Heiko Stübner" <heiko@sntech.de>]

Hi,

Am Dienstag, 12. Oktober 2021, 18:40:26 CEST schrieb Anup Patel:
> On Tue, Oct 12, 2021 at 9:04 PM <guoren@kernel.org> wrote:
> >
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > thead,c9xx-plic would mask IRQ with readl(claim), so it needn't
> > mask/unmask which needed in RISC-V PLIC.
> >
> > When in IRQS_ONESHOT & IRQCHIP_EOI_THREADED path, unnecessary mask
> > operation would cause a blocking irq bug in thead,c9xx-plic. Because
> > when IRQ is disabled in c9xx, writel(hwirq, claim) would be invalid.
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Cc: Anup Patel <anup@brainfault.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Palmer Dabbelt <palmer@dabbelt.com>
> > Cc: Atish Patra <atish.patra@wdc.com>
> >
> > ---
> >
> > Changes since V2:
> >  - Add a separate compatible string "thead,c9xx-plic"
> >  - set irq_mask/unmask of "plic_chip" to NULL and point
> >    irq_enable/disable of "plic_chip" to plic_irq_mask/unmask
> >  - Add a detailed comment block in plic_init() about the
> >    differences in Claim/Completion process of RISC-V PLIC and C9xx
> >    PLIC.
> > ---
> >  drivers/irqchip/irq-sifive-plic.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
> > index cf74cfa82045..3756b1c147c3 100644
> > --- a/drivers/irqchip/irq-sifive-plic.c
> > +++ b/drivers/irqchip/irq-sifive-plic.c
> > @@ -79,6 +79,7 @@ struct plic_handler {
> >  };
> >  static int plic_parent_irq __ro_after_init;
> >  static bool plic_cpuhp_setup_done __ro_after_init;
> > +static bool disable_mask_unmask __ro_after_init;
> >  static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
> >
> >  static inline void plic_toggle(struct plic_handler *handler,
> > @@ -181,6 +182,13 @@ static int plic_irqdomain_map(struct irq_domain *d, unsigned int irq,
> >  {
> >         struct plic_priv *priv = d->host_data;
> >
> > +       if (disable_mask_unmask) {
> > +               plic_chip.irq_mask      = NULL;
> > +               plic_chip.irq_unmask    = NULL;
> > +               plic_chip.irq_enable    = plic_irq_unmask;
> > +               plic_chip.irq_disable   = plic_irq_mask;
> > +       }
> > +
> >         irq_domain_set_info(d, irq, hwirq, &plic_chip, d->host_data,
> >                             handle_fasteoi_irq, NULL, NULL);
> >         irq_set_noprobe(irq);
> > @@ -390,5 +398,14 @@ static int __init plic_init(struct device_node *node,
> >         return error;
> >  }
> >
> > +static int __init thead_c9xx_plic_init(struct device_node *node,
> > +               struct device_node *parent)
> > +{
> > +       disable_mask_unmask = true;
> 
> The plic_irqdomain_map() is called for each irq so "plic_chip"
> will be updated multiple times.
> 
> You can drop the disable_mask_unmask variable and instead
> directly update "plic_chip" here.

Actually I'd think something more dynamic might be appropriate?

I.e. don't modify the generic plic_chip structure, but define a second
one for this type of chip and reference that one in plic_irqdomain_map
depending on the block found?

According to [0] a system can have multiple PLICs and nothing
guarantees that they'll always be the same variant on future socs
[hardware engineers are very creative]

So adding more stuff that modifies static content used by all PLICs
doesn't really improve driver quality here ;-)


Heiko


[0] https://lore.kernel.org/linux-riscv/1839bf9ef91de2358a7e8ecade361f7a@www.loen.fr/T/


> 
> > +
> > +       return plic_init(node, parent);
> > +}
> > +
> >  IRQCHIP_DECLARE(sifive_plic, "sifive,plic-1.0.0", plic_init);
> >  IRQCHIP_DECLARE(riscv_plic0, "riscv,plic0", plic_init); /* for legacy systems */
> > +IRQCHIP_DECLARE(thead_c9xx_plic, "thead,c9xx-plic", thead_c9xx_plic_init);
> > --
> > 2.25.1
> >
> 
> Regards,
> Anup
> 
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