[PATCH] lib: sbi: Enable M-mode external interrupt only for AIA

[Jessica Clarke]

On 18 Feb 2022, at 16:56, Atish Patra <atishp at rivosinc.com> wrote:
> 
> Some platforms may inject spurious M-mode external interrupt if
> the external interrupt bit is enabled in mie. We really don't
> need to enable M-mode external interrupts for platforms without
> AIA. This issue is observed in HiFive unmatched.
> 
> Keep the M-mode external interrupt disabled for non-AIA platforms.

Is this for UART1 (https://forums.sifive.com/t/spurious-interrupts-from-m-2-e-key-uart1/5478)?

Seems to be OpenSBI should not be enabling any external interrupts in
the PLIC that it doesn’t want, which should render this patch
unnecessary (though you could perhaps argue you still might as well not
unmask external interrupts if you don’t expect any). Otherwise you just
risk the same thing happening for AIA hardware and needing to do the
proper fix at a later date.

As it stands this patch is quite dubious without further exploration
and explanation of where these external interrupts are coming from.

Jess

> Signed-off-by: Atish Patra <atishp at rivosinc.com>
> ---
> lib/sbi/sbi_init.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/sbi/sbi_init.c b/lib/sbi/sbi_init.c
> index 6876eb2f0f22..76b7c5d953ec 100644
> --- a/lib/sbi/sbi_init.c
> +++ b/lib/sbi/sbi_init.c
> @@ -276,7 +276,12 @@ static void __noreturn init_coldboot(struct sbi_scratch *scratch, u32 hartid)
> 			   __func__, rc);
> 		sbi_hart_hang();
> 	}
> -	csr_set(CSR_MIE, MIP_MEIP);
> +	/**
> +	 * HiFive unmatched platform generates spurious interrupt if external
> +	 * interrupt is enabled in mie. Enable it only if AIA is present.
> +	 */
> +	if (sbi_hart_has_feature(scratch, SBI_HART_HAS_AIA))
> +		csr_set(CSR_MIE, MIP_MEIP);
> 
> 	rc = sbi_ipi_init(scratch, TRUE);
> 	if (rc) {
> @@ -377,7 +382,12 @@ static void init_warm_startup(struct sbi_scratch *scratch, u32 hartid)
> 	rc = sbi_platform_irqchip_init(plat, FALSE);
> 	if (rc)
> 		sbi_hart_hang();
> -	csr_set(CSR_MIE, MIP_MEIP);
> +	/**
> +	 * HiFive unmatched platform generates spurious interrupt if external
> +	 * interrupt is enabled in mie. Enable it only if AIA is present.
> +	 */
> +	if (sbi_hart_has_feature(scratch, SBI_HART_HAS_AIA))
> +		csr_set(CSR_MIE, MIP_MEIP);
> 
> 	rc = sbi_ipi_init(scratch, FALSE);
> 	if (rc)
> -- 
> 2.30.2
> 
> 
> -- 
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