linux-kernel - Re: [PATCH v13 06/13] irqchip: Add RISC-V incoming MSI controller early driver

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Date: Tue, 20 Feb 2024 14:15:56 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Anup Patel <apatel@...tanamicro.com>, Palmer Dabbelt
 <palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>, Rob
 Herring <robh+dt@...nel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>, Frank Rowand
 <frowand.list@...il.com>, Conor Dooley <conor+dt@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>, Björn Töpel
 <bjorn@...nel.org>, Atish
 Patra <atishp@...shpatra.org>, Andrew Jones <ajones@...tanamicro.com>,
 Sunil V L <sunilvl@...tanamicro.com>, Saravana Kannan
 <saravanak@...gle.com>, Anup Patel <anup@...infault.org>,
 linux-riscv@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, Anup Patel
 <apatel@...tanamicro.com>
Subject: Re: [PATCH v13 06/13] irqchip: Add RISC-V incoming MSI controller
 early driver

On Tue, Feb 20 2024 at 11:37, Anup Patel wrote:
> The RISC-V advanced interrupt architecture (AIA) specification
> defines a new MSI controller called incoming message signalled
> interrupt controller (IMSIC) which manages MSI on per-HART (or
> per-CPU) basis. It also supports IPIs as software injected MSIs.
> (For more details refer https://github.com/riscv/riscv-aia)
>
> Let us add an early irqchip driver for RISC-V IMSIC which sets
> up the IMSIC state and provide IPIs.

s/Let us add/Add/

> +#else
> +static void imsic_ipi_starting_cpu(void)
> +{
> +}
> +
> +static void imsic_ipi_dying_cpu(void)
> +{
> +}
> +
> +static int __init imsic_ipi_domain_init(void)
> +{
> +	return 0;
> +}

Please condense this into

static void imsic_ipi_starting_cpu(void) { }
static void imsic_ipi_dying_cpu(void) { }
static int __init imsic_ipi_domain_init(void) { return 0; }

No point in wasting space for these stubs.

> + * To handle an interrupt, we read the TOPEI CSR and write zero in one
> + * instruction. If TOPEI CSR is non-zero then we translate TOPEI.ID to
> + * Linux interrupt number and let Linux IRQ subsystem handle it.
> + */
> +static void imsic_handle_irq(struct irq_desc *desc)
> +{
> +	struct irq_chip *chip = irq_desc_get_chip(desc);
> +	int err, cpu = smp_processor_id();
> +	struct imsic_vector *vec;
> +	unsigned long local_id;
> +
> +	chained_irq_enter(chip, desc);
> +
> +	while ((local_id = csr_swap(CSR_TOPEI, 0))) {
> +		local_id = local_id >> TOPEI_ID_SHIFT;
> +
> +		if (local_id == IMSIC_IPI_ID) {
> +#ifdef CONFIG_SMP

	if (IS_ENABLED(CONFIG_SMP))

> +			ipi_mux_process();
> +#endif
> +			continue;
> +		}

> +
> +/* MUST be called with lpriv->lock held */

Instead of a comment which cannot be enforced just have

        lockdep_assert_held(&lpriv->lock);

right at the top of the function. That documents the requirement and
lets lockdep yell if not followed.

> +#ifdef CONFIG_SMP
> +static void imsic_local_timer_callback(struct timer_list *timer)
> +{
> +	struct imsic_local_priv *lpriv = this_cpu_ptr(imsic->lpriv);
> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&lpriv->lock, flags);
> +	__imsic_local_sync(lpriv);
> +	raw_spin_unlock_irqrestore(&lpriv->lock, flags);
> +}
> +
> +/* MUST be called with lpriv->lock held */

Ditto

> +static void __imsic_remote_sync(struct imsic_local_priv *lpriv, unsigned int cpu)

> +void imsic_vector_mask(struct imsic_vector *vec)
> +{
> +	struct imsic_local_priv *lpriv;
> +
> +	lpriv = per_cpu_ptr(imsic->lpriv, vec->cpu);
> +	if (WARN_ON(&lpriv->vectors[vec->local_id] != vec))
> +		return;

WARN_ON_ONCE(), no?

> +bool imsic_vector_isenabled(struct imsic_vector *vec)
> +{
> +	struct imsic_local_priv *lpriv = per_cpu_ptr(imsic->lpriv, vec->cpu);
> +	unsigned long flags;
> +	bool ret;
> +
> +	raw_spin_lock_irqsave(&lpriv->lock, flags);
> +	ret = vec->enable;
> +	raw_spin_unlock_irqrestore(&lpriv->lock, flags);

I'm not sure what you are trying to protect here. vec->enable can
obviously change right after the lock is dropped. So that's just a
snapshot, which is not any better than using

          READ_ONCE(vec->enable);

and a corresponding WRITE_ONCE() at the update site, which obviously
needs serialization.

> +static void __init imsic_local_cleanup(void)
> +{
> +	int cpu;
> +	struct imsic_local_priv *lpriv;

        struct imsic_local_priv *lpriv;
	int cpu;

Please.

> +void imsic_state_offline(void)
> +{
> +#ifdef CONFIG_SMP
> +	struct imsic_local_priv *lpriv = this_cpu_ptr(imsic->lpriv);
> +#endif

You can move that into the #ifdef below.

> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&imsic->matrix_lock, flags);
> +	irq_matrix_offline(imsic->matrix);
> +	raw_spin_unlock_irqrestore(&imsic->matrix_lock, flags);
> +
> +#ifdef CONFIG_SMP
> +	raw_spin_lock_irqsave(&lpriv->lock, flags);
> +	WARN_ON_ONCE(try_to_del_timer_sync(&lpriv->timer) < 0);
> +	raw_spin_unlock_irqrestore(&lpriv->lock, flags);
> +#endif
> +}


Thanks,

        tglx