linux-kernel - Re: [PATCH v2 4/4] RISC-V: Move to the new generic IRQ handler

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Date:   Thu, 25 Jan 2018 17:31:53 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Palmer Dabbelt <palmer@...ive.com>
Cc:     linux@...linux.org.uk, catalin.marinas@....com,
        Will Deacon <will.deacon@....com>, jonas@...thpole.se,
        stefan.kristiansson@...nalahti.fi, tglx@...utronix.de,
        Christoph Hellwig <hch@...radead.org>,
        Arnd Bergmann <arnd@...db.de>, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, patches@...ups.riscv.org
Subject: Re: [PATCH v2 4/4] RISC-V: Move to the new generic IRQ handler

On Wed, Jan 24, 2018 at 07:07:56PM -0800, Palmer Dabbelt wrote:
> The old mechanism for handling IRQs on RISC-V was pretty ugly: the arch
> code looked at the Kconfig entry for our first-level irqchip driver and
> called into it directly.
> 
> This patch uses the new 0generic IRQ handling infastructure, which
> essentially just deletes a bunch of code.  This does add an additional
> load to the interrupt latency, but there's a lot of tuning left to be
> done there on RISC-V so I think it's OK for now.
> 
> Signed-off-by: Palmer Dabbelt <palmer@...ive.com>
> ---
>  arch/riscv/Kconfig            |  1 +
>  arch/riscv/include/asm/Kbuild |  1 +
>  arch/riscv/kernel/entry.S     |  5 +++--
>  arch/riscv/kernel/irq.c       | 13 -------------
>  4 files changed, 5 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 2c6adf12713a..e67f42178059 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -35,6 +35,7 @@ config RISCV
>  	select THREAD_INFO_IN_TASK
>  	select RISCV_IRQ_INTC
>  	select RISCV_TIMER
> +	select MULTI_IRQ_HANDLER
>  
>  config MMU
>  	def_bool y
> diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
> index 970460a0b492..e0d0fbe43ca2 100644
> --- a/arch/riscv/include/asm/Kbuild
> +++ b/arch/riscv/include/asm/Kbuild
> @@ -16,6 +16,7 @@ generic-y += ftrace.h
>  generic-y += futex.h
>  generic-y += hardirq.h
>  generic-y += hash.h
> +generic-y += handle_irq.h
>  generic-y += hw_irq.h
>  generic-y += ioctl.h
>  generic-y += ioctls.h
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 7404ec222406..a79869151aea 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -166,8 +166,9 @@ ENTRY(handle_exception)
>  	/* Handle interrupts */
>  	slli a0, s4, 1
>  	srli a0, a0, 1

Hi Palmer,

Do we need these shifts into a0?  I guess these were used when this was an arg
to  do_IRQ, but no longer needed since you put pt_regs into a0 in the next
instruction.

Other than that it looks good, and thanks for looking at OpenRISC too.

Acked-by: Stafford Horne <shorne@...il.com>


> -	move a1, sp /* pt_regs */
> -	tail do_IRQ
> +	move a0, sp /* pt_regs */
> +	REG_L a1, handle_arch_irq
> +	jr a1
>  1:
>  	/* Handle syscalls */
>  	li t0, EXC_SYSCALL
> diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
> index 328718e8026e..b74cbfbce2d0 100644
> --- a/arch/riscv/kernel/irq.c
> +++ b/arch/riscv/kernel/irq.c
> @@ -24,16 +24,3 @@ void __init init_IRQ(void)
>  {
>  	irqchip_init();
>  }
> -
> -asmlinkage void __irq_entry do_IRQ(unsigned int cause, struct pt_regs *regs)
> -{
> -#ifdef CONFIG_RISCV_INTC
> -	/*
> -	 * FIXME: We don't want a direct call to riscv_intc_irq here.  The plan
> -	 * is to put an IRQ domain here and let the interrupt controller
> -	 * register with that, but I poked around the arm64 code a bit and
> -	 * there might be a better way to do it (ie, something fully generic).
> -	 */
> -	riscv_intc_irq(cause, regs);
> -#endif
> -}
> -- 
> 2.13.6
>