Re: [PATCH v2 7/8] tty: Add SBI debug console support to HVC SBI driver

Anup Patel
2023-10-13T15:42:07Z

On Thu, Oct 12, 2023 at 5:08 PM Björn Töpel <bjorn@kernel.org> wrote:
>
> Anup Patel <apatel@ventanamicro.com> writes:
>
> > From: Atish Patra <atishp@rivosinc.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@rivosinc.com>
> > Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> > ---
> > drivers/tty/hvc/Kconfig | 2 +-
> > drivers/tty/hvc/hvc_riscv_sbi.c | 76 ++++++++++++++++++++++++++++++---
> > 2 files changed, 70 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..da318d7f55c5 100644
> > --- a/drivers/tty/hvc/hvc_riscv_sbi.c
> > +++ b/drivers/tty/hvc/hvc_riscv_sbi.c
> > @@ -39,21 +39,83 @@ 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);
>
> What is assumed from buf here? If buf is crossing a page, you need to
> adjust the count, no?

I never saw a page crossing buffer but I will certainly address this
in the next revision.

>
> > + 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;
> > }
> > -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);
>
> And definitely adjust count here, if we're crossing a page!

Sure, I will update here as well.

Thanks,
Anup