Re: [RFC PATCH 5/7] riscv: add double trap driver

[Conor Dooley <conor@kernel.org>]

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On Thu, Apr 18, 2024 at 04:26:44PM +0200, Clément Léger wrote:
> Add a small driver to request double trap enabling as well as
> registering a SSE handler for double trap. This will also be used by KVM
> SBI FWFT extension support to detect if it is possible to enable double
> trap in VS-mode.
> 
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> ---
>  arch/riscv/include/asm/sbi.h    |  1 +
>  drivers/firmware/Kconfig        |  7 +++
>  drivers/firmware/Makefile       |  1 +
>  drivers/firmware/riscv_dbltrp.c | 95 +++++++++++++++++++++++++++++++++
>  include/linux/riscv_dbltrp.h    | 19 +++++++
>  5 files changed, 123 insertions(+)
>  create mode 100644 drivers/firmware/riscv_dbltrp.c
>  create mode 100644 include/linux/riscv_dbltrp.h
> 
> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> index 744aa1796c92..9cd4ca66487c 100644
> --- a/arch/riscv/include/asm/sbi.h
> +++ b/arch/riscv/include/asm/sbi.h
> @@ -314,6 +314,7 @@ enum sbi_sse_attr_id {
>  #define SBI_SSE_ATTR_INTERRUPTED_FLAGS_SPIE	(1 << 2)
>  
>  #define SBI_SSE_EVENT_LOCAL_RAS		0x00000000
> +#define SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP	0x00000001
>  #define SBI_SSE_EVENT_GLOBAL_RAS	0x00008000
>  #define SBI_SSE_EVENT_LOCAL_PMU		0x00010000
>  #define SBI_SSE_EVENT_LOCAL_SOFTWARE	0xffff0000
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index 59f611288807..a037f6e89942 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -197,6 +197,13 @@ config RISCV_SSE_TEST
>  	  Select if you want to enable SSE extension testing at boot time.
>  	  This will run a series of test which verifies SSE sanity.
>  
> +config RISCV_DBLTRP
> +	bool "Enable Double trap handling"
> +	depends on RISCV_SSE && RISCV_SBI
> +	default n
> +	help
> +	  Select if you want to enable SSE double trap handler.
> +
>  config SYSFB
>  	bool
>  	select BOOT_VESA_SUPPORT
> diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
> index fb7b0c08c56d..ad67a1738c0f 100644
> --- a/drivers/firmware/Makefile
> +++ b/drivers/firmware/Makefile
> @@ -18,6 +18,7 @@ obj-$(CONFIG_RASPBERRYPI_FIRMWARE) += raspberrypi.o
>  obj-$(CONFIG_FW_CFG_SYSFS)	+= qemu_fw_cfg.o
>  obj-$(CONFIG_RISCV_SSE)		+= riscv_sse.o
>  obj-$(CONFIG_RISCV_SSE_TEST)	+= riscv_sse_test.o
> +obj-$(CONFIG_RISCV_DBLTRP)	+= riscv_dbltrp.o

As previously mentioned, I'd like to see all of these riscv specific
things in a riscv directory.

>  obj-$(CONFIG_SYSFB)		+= sysfb.o
>  obj-$(CONFIG_SYSFB_SIMPLEFB)	+= sysfb_simplefb.o
>  obj-$(CONFIG_TI_SCI_PROTOCOL)	+= ti_sci.o
> diff --git a/drivers/firmware/riscv_dbltrp.c b/drivers/firmware/riscv_dbltrp.c
> new file mode 100644
> index 000000000000..72f9a067e87a
> --- /dev/null
> +++ b/drivers/firmware/riscv_dbltrp.c
> @@ -0,0 +1,95 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2023 Rivos Inc.
> + */
> +
> +#define pr_fmt(fmt) "riscv-dbltrp: " fmt
> +
> +#include <linux/cpu.h>
> +#include <linux/init.h>
> +#include <linux/riscv_dbltrp.h>
> +#include <linux/riscv_sse.h>
> +
> +#include <asm/sbi.h>
> +
> +static bool double_trap_enabled;
> +
> +static int riscv_sse_dbltrp_handle(uint32_t evt, void *arg,
> +				   struct pt_regs *regs)
> +{
> +	__show_regs(regs);
> +	panic("Double trap !\n");
> +
> +	return 0;
> +}
> +
> +struct cpu_dbltrp_data {
> +	int error;
> +};
> +
> +static void
> +sbi_cpu_enable_double_trap(void *data)

This should easily fit on one line.

> +{
> +	struct sbiret ret;
> +	struct cpu_dbltrp_data *cdd = data;
> +
> +	ret = sbi_ecall(SBI_EXT_FWFT, SBI_EXT_FWFT_SET,
> +			SBI_FWFT_DOUBLE_TRAP_ENABLE, 1, 0, 0, 0, 0);
> +
> +	if (ret.error) {
> +		cdd->error = 1;

If this is a boolean, make it a boolean please. All the code in this
patch treats it as one.

> +		pr_err("Failed to enable double trap on cpu %d\n", smp_processor_id());
> +	}
> +}
> +
> +static int sbi_enable_double_trap(void)
> +{
> +	struct cpu_dbltrp_data cdd = {0};
> +
> +	on_each_cpu(sbi_cpu_enable_double_trap, &cdd, 1);
> +	if (cdd.error)
> +		return -1;

Can this be an errno please?

> +
> +	double_trap_enabled = true;
> +
> +	return 0;
> +}
> +
> +bool riscv_double_trap_enabled(void)
> +{
> +	return double_trap_enabled;
> +}
> +EXPORT_SYMBOL(riscv_double_trap_enabled);

Can we just use double_trap everywhere? dbltrp reads like sound that a
beatboxer would make and this looks a lot nicer than the other functions
in the file...

> +
> +static int __init riscv_dbltrp(void)

I think this function is missing an action work - init or probe?

> +{
> +	struct sse_event *evt;
> +
> +	if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SSDBLTRP)) {
> +		pr_err("Ssdbltrp extension not available\n");
> +		return 1;
> +	}
> +
> +	if (!sbi_probe_extension(SBI_EXT_FWFT)) {
> +		pr_err("Can not enable double trap, SBI_EXT_FWFT is not available\n");
> +		return 1;
> +	}
> +
> +	if (sbi_enable_double_trap()) {
> +		pr_err("Failed to enable double trap on all cpus\n");
> +		return 1;

Why do we return 1s here, but an errno via PTR_ERR() below?
Shouldn't all of these be returning a negative errono?
This particular one should probably propagate the error it got from
sbi_enable_double_trap().

Cheers,
Conor.

> +	}
> +
> +	evt = sse_event_register(SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP, 0,
> +				 riscv_sse_dbltrp_handle, NULL);
> +	if (IS_ERR(evt)) {
> +		pr_err("SSE double trap register failed\n");
> +		return PTR_ERR(evt);
> +	}
> +
> +	sse_event_enable(evt);
> +	pr_info("Double trap handling registered\n");
> +
> +	return 0;
> +}
> +device_initcall(riscv_dbltrp);
> diff --git a/include/linux/riscv_dbltrp.h b/include/linux/riscv_dbltrp.h
> new file mode 100644
> index 000000000000..6de4f43fae6b
> --- /dev/null
> +++ b/include/linux/riscv_dbltrp.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2023 Rivos Inc.
> + */
> +
> +#ifndef __LINUX_RISCV_DBLTRP_H
> +#define __LINUX_RISCV_DBLTRP_H
> +
> +#if defined(CONFIG_RISCV_DBLTRP)
> +bool riscv_double_trap_enabled(void);
> +#else
> +
> +static inline bool riscv_double_trap_enabled(void)
> +{
> +	return false;
> +}
> +#endif
> +
> +#endif /* __LINUX_RISCV_DBLTRP_H */
> -- 
> 2.43.0
> 

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