linux-kernel - Re: [PATCH v3 8/9] tty: Add SBI debug console support to HVC SBI driver

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Message-ID: <20231020-f1ec2b7e384a4cfeae39966f@orel>
Date:   Fri, 20 Oct 2023 12:46:46 +0200
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Anup Patel <apatel@...tanamicro.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Atish Patra <atishp@...shpatra.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Conor Dooley <conor@...nel.org>, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-serial@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Atish Patra <atishp@...osinc.com>
Subject: Re: [PATCH v3 8/9] tty: Add SBI debug console support to HVC SBI
 driver

On Fri, Oct 20, 2023 at 12:51:39PM +0530, Anup Patel wrote:
> From: Atish Patra <atishp@...osinc.com>
> 
> RISC-V SBI specification supports advanced debug console
> support via SBI DBCN extension.
> 
> Extend the HVC SBI driver to support it.
> 
> Signed-off-by: Atish Patra <atishp@...osinc.com>
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> ---
>  drivers/tty/hvc/Kconfig         |  2 +-
>  drivers/tty/hvc/hvc_riscv_sbi.c | 82 ++++++++++++++++++++++++++++++---
>  2 files changed, 76 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
> index 4f9264d005c0..6e05c5c7bca1 100644
> --- a/drivers/tty/hvc/Kconfig
> +++ b/drivers/tty/hvc/Kconfig
> @@ -108,7 +108,7 @@ config HVC_DCC_SERIALIZE_SMP
>  
>  config HVC_RISCV_SBI
>  	bool "RISC-V SBI console support"
> -	depends on RISCV_SBI_V01
> +	depends on RISCV_SBI
>  	select HVC_DRIVER
>  	help
>  	  This enables support for console output via RISC-V SBI calls, which
> diff --git a/drivers/tty/hvc/hvc_riscv_sbi.c b/drivers/tty/hvc/hvc_riscv_sbi.c
> index 31f53fa77e4a..56da1a4b5aca 100644
> --- a/drivers/tty/hvc/hvc_riscv_sbi.c
> +++ b/drivers/tty/hvc/hvc_riscv_sbi.c
> @@ -39,21 +39,89 @@ static int hvc_sbi_tty_get(uint32_t vtermno, char *buf, int count)
>  	return i;
>  }
>  
> -static const struct hv_ops hvc_sbi_ops = {
> +static const struct hv_ops hvc_sbi_v01_ops = {
>  	.get_chars = hvc_sbi_tty_get,
>  	.put_chars = hvc_sbi_tty_put,
>  };
>  
> -static int __init hvc_sbi_init(void)
> +static int hvc_sbi_dbcn_tty_put(uint32_t vtermno, const char *buf, int count)
>  {
> -	return PTR_ERR_OR_ZERO(hvc_alloc(0, 0, &hvc_sbi_ops, 16));
> +	phys_addr_t pa;
> +	struct sbiret ret;
> +
> +	if (is_vmalloc_addr(buf)) {
> +		pa = page_to_phys(vmalloc_to_page(buf)) + offset_in_page(buf);
> +		if (PAGE_SIZE < (offset_in_page(buf) + count))

I thought checkpatch complained about uppercase constants being on the
left in comparisons.

> +			count = PAGE_SIZE - offset_in_page(buf);
> +	} else {
> +		pa = __pa(buf);
> +	}
> +
> +	if (IS_ENABLED(CONFIG_32BIT))
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_WRITE,
> +				count, lower_32_bits(pa), upper_32_bits(pa),
> +				0, 0, 0);
> +	else
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_WRITE,
> +				count, pa, 0, 0, 0, 0);
> +	if (ret.error)
> +		return 0;
> +
> +	return count;

Shouldn't we return ret.value here in case it's less than count? I see we
already do that below in get().

>  }
> -device_initcall(hvc_sbi_init);
>  
> -static int __init hvc_sbi_console_init(void)
> +static int hvc_sbi_dbcn_tty_get(uint32_t vtermno, char *buf, int count)
>  {
> -	hvc_instantiate(0, 0, &hvc_sbi_ops);
> +	phys_addr_t pa;
> +	struct sbiret ret;
> +
> +	if (is_vmalloc_addr(buf)) {
> +		pa = page_to_phys(vmalloc_to_page(buf)) + offset_in_page(buf);
> +		if (PAGE_SIZE < (offset_in_page(buf) + count))
> +			count = PAGE_SIZE - offset_in_page(buf);
> +	} else {
> +		pa = __pa(buf);
> +	}
> +
> +	if (IS_ENABLED(CONFIG_32BIT))
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_READ,
> +				count, lower_32_bits(pa), upper_32_bits(pa),
> +				0, 0, 0);
> +	else
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_READ,
> +				count, pa, 0, 0, 0, 0);
> +	if (ret.error)
> +		return 0;
> +
> +	return ret.value;
> +}
> +
> +static const struct hv_ops hvc_sbi_dbcn_ops = {
> +	.put_chars = hvc_sbi_dbcn_tty_put,
> +	.get_chars = hvc_sbi_dbcn_tty_get,
> +};
> +
> +static int __init hvc_sbi_init(void)
> +{
> +	int err;
> +
> +	if ((sbi_spec_version >= sbi_mk_version(2, 0)) &&
> +	    (sbi_probe_extension(SBI_EXT_DBCN) > 0)) {
> +		err = PTR_ERR_OR_ZERO(hvc_alloc(0, 0, &hvc_sbi_dbcn_ops, 16));

Why an outbuf size of only 16?

> +		if (err)
> +			return err;
> +		hvc_instantiate(0, 0, &hvc_sbi_dbcn_ops);
> +	} else {
> +		if (IS_ENABLED(CONFIG_RISCV_SBI_V01)) {
> +			err = PTR_ERR_OR_ZERO(hvc_alloc(0, 0, &hvc_sbi_v01_ops, 16));
> +			if (err)
> +				return err;
> +			hvc_instantiate(0, 0, &hvc_sbi_v01_ops);
> +		} else {
> +			return -ENODEV;
> +		}
> +	}
>  
>  	return 0;
>  }
> -console_initcall(hvc_sbi_console_init);
> +device_initcall(hvc_sbi_init);
> -- 
> 2.34.1
>

Thanks,
drew