linux-kernel - Re: [PATCH v4 4/5] tty: Add SBI debug console support to HVC SBI driver

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Message-ID: <CAHBxVyG-DK9cDqPedJcR2W2=LQFumQQ_0Z0UUdbbzgju7BaAtg@mail.gmail.com>
Date:   Tue, 21 Nov 2023 00:21:11 -0800
From:   Atish Kumar Patra <atishp@...osinc.com>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Anup Patel <apatel@...tanamicro.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Conor Dooley <conor@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        linux-riscv@...ts.infradead.org, linux-serial@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/5] tty: Add SBI debug console support to HVC SBI driver

On Sun, Nov 19, 2023 at 11:16 PM Jiri Slaby <jirislaby@...nel.org> wrote:
>
> On 18. 11. 23, 4:38, Anup Patel wrote:
> > diff --git a/drivers/tty/hvc/hvc_riscv_sbi.c b/drivers/tty/hvc/hvc_riscv_sbi.c
> > index 31f53fa77e4a..697c981221b5 100644
> > --- a/drivers/tty/hvc/hvc_riscv_sbi.c
> > +++ b/drivers/tty/hvc/hvc_riscv_sbi.c
> ...
> > -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;
> > +
> > +     if (is_vmalloc_addr(buf)) {
>
> I wonder, where does this buf come from, so that you have to check for
> vmalloc?
>

When VMAP_STCK is enabled, stack allocation depends on the vmalloc.
That's why we have to if the buf is allocated using vmalloc.

> > +             pa = page_to_phys(vmalloc_to_page(buf)) + offset_in_page(buf);
> > +             if (PAGE_SIZE < (offset_in_page(buf) + count))
>
> Am I the only one who would prefer:
>    if (count + offset_in_page(buf) > PAGE_SIZE)
> ?
>
> > +                     count = PAGE_SIZE - offset_in_page(buf);
> > +     } else {
> > +             pa = __pa(buf);
> > +     }
> > +
> > +     return sbi_debug_console_read(count, pa);
> > +}
>
>
> thanks,
> --
> js
> suse labs
>