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Date:   Wed, 13 Oct 2021 16:38:53 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Atish Patra <atish.patra@....com>, Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Palmer Dabbelt <palmer@...belt.com>,
        Heiko Stübner <heiko@...ech.de>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V3 2/2] irqchip/sifive-plic: Add thead,c900-plic support

On Wed, Oct 13, 2021 at 1:04 PM Anup Patel <anup@...infault.org> wrote:
>
> On Wed, Oct 13, 2021 at 6:52 AM <guoren@...nel.org> wrote:
> >
> > From: Guo Ren <guoren@...ux.alibaba.com>
> >
> > thead,c900-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,c900-plic. Because
> > when IRQ is disabled in c900, writel(hwirq, claim) would be invalid.
>
> This is a totally incorrect description.
>
> Instead of this, the commit description should say the following:
>
> 1) The irq_mask/unmask() is used by handle_fasteoi_irq() is mostly
> for ONESHOT irqs and there is no limitation in the RISC-V PLIC driver
> due to use of irq_mask/unmask() callbacks. In fact, a lot of irqchip
> drivers using handle_fasteoi_irq() also implement irq_mask/unmask().
Add irq_mask/unmask in handle_fasteoi_irq() would decrease the
performance, we also need to add this fact in the description.
>
> 2) The C9xx PLIC does not comply with the interrupt claim/completion
> process defined by the RISC-V PLIC specification because C9xx PLIC
> will mask an IRQ when it is claimed by PLIC driver (i.e. readl(claim) and
> the IRQ will be unmasked upon completion by PLIC driver (i.e. writel(claim).
> This behaviour breaks the handling of IRQS_ONESHOT by the generic
> handle_fasteoi_irq() used in the PLIC driver.
>
> 3) This patch adds an errata fix for IRQS_ONESHOT handling on
> C9xx PLIC by using irq_enable/disable() callbacks instead of
> irq_mask/unmask().
>
> In general, non-compliance of the C9xx PLIC should be treated as
> an errata so please don't project it as a feature.
>
> >
> > Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> > Cc: Anup Patel <anup@...infault.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Marc Zyngier <maz@...nel.org>
> > Cc: Palmer Dabbelt <palmer@...belt.com>
> > Cc: Atish Patra <atish.patra@....com>
> >
> > ---
> >
> > Changes since V3:
> >  - Rename "c9xx" to "c900"
> >  - Add sifive_plic_chip and thead_plic_chip for difference
> >
> > 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 | 25 +++++++++++++++++++++++--
> >  1 file changed, 23 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
> > index cf74cfa82045..5b806d823df7 100644
> > --- a/drivers/irqchip/irq-sifive-plic.c
> > +++ b/drivers/irqchip/irq-sifive-plic.c
> > @@ -166,7 +166,7 @@ static void plic_irq_eoi(struct irq_data *d)
> >         writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
> >  }
> >
> > -static struct irq_chip plic_chip = {
> > +static struct irq_chip sifive_plic_chip = {
> >         .name           = "SiFive PLIC",
> >         .irq_mask       = plic_irq_mask,
> >         .irq_unmask     = plic_irq_unmask,
> > @@ -176,12 +176,24 @@ static struct irq_chip plic_chip = {
> >  #endif
> >  };
> >
>
> Please add a detailed comment block as described by point#2
> above.
>
> > +static struct irq_chip thead_plic_chip = {
> > +       .name           = "T-Head PLIC",
> > +       .irq_disable    = plic_irq_mask,
> > +       .irq_enable     = plic_irq_unmask,
> > +       .irq_eoi        = plic_irq_eoi,
> > +#ifdef CONFIG_SMP
> > +       .irq_set_affinity = plic_set_affinity,
> > +#endif
> > +};
> > +
> > +static struct irq_chip *def_plic_chip = &sifive_plic_chip;
> > +
> >  static int plic_irqdomain_map(struct irq_domain *d, unsigned int irq,
> >                               irq_hw_number_t hwirq)
> >  {
> >         struct plic_priv *priv = d->host_data;
> >
> > -       irq_domain_set_info(d, irq, hwirq, &plic_chip, d->host_data,
> > +       irq_domain_set_info(d, irq, hwirq, def_plic_chip, d->host_data,
> >                             handle_fasteoi_irq, NULL, NULL);
> >         irq_set_noprobe(irq);
> >         irq_set_affinity(irq, &priv->lmask);
> > @@ -390,5 +402,14 @@ static int __init plic_init(struct device_node *node,
> >         return error;
> >  }
> >
> > +static int __init thead_c900_plic_init(struct device_node *node,
> > +               struct device_node *parent)
> > +{
> > +       def_plic_chip = &thead_plic_chip;
> > +
> > +       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_c900_plic, "thead,c900-plic", thead_c900_plic_init);
> > --
> > 2.25.1
> >
>
> Regards,
> Anup



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/

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