Re: [PATCH] tty: Don't force RISCV SBI console as preferred console

[Atish Patra]

On 4/25/19 11:21 PM, Anup Patel wrote:
> On Fri, Apr 26, 2019 at 10:11 AM Atish Patra <atish.patra@xxxxxxx> wrote:
> > On 4/25/19 6:35 AM, Anup Patel wrote:
> > > The Linux kernel will auto-disables all boot consoles whenever it
> > > gets a preferred real console.
> > >
> > > Currently on RISC-V systems, if we have a real console which is not
> > > RISCV SBI console then boot consoles (such as earlycon=sbi) are not
> > > auto-disabled when a real console (ttyS0 or ttySIF0) is available.
> > > This results in duplicate prints at boot-time after kernel starts
> > > using real console (i.e. ttyS0 or ttySIF0) if "earlycon=" kernel
> > > parameter was passed by bootloader.
> > >
> > > The reason for above issue is that RISCV SBI console always adds
> > > itself as preferred console which is causing other real consoles
> > > to be not used as preferred console.
> >
> > Do we even need HVC_SBI console to be enabled by default? Disabling
> > CONFIG_HVC_RISCV_SBI seems to be fine while running in QEMU.
>
> Actually, HVC_SBI console is useful on boards (such as SiFive Unleashed)
> lacking upstream serial driver. It allows us to boot upstream kernel to prompt
> on such boards with just timer driver (and probably irqchip driver).
>
> Also, we should be able to use same kernel image on QEMU and SiFive
> Unleashed board so disabling CONFIG_HVC_RISCV_SBI for QEMU is
> a temporary solution.
>
> > If we don't need it, I suggest we should remove the config option from
> > defconfig in addition to this patch.
>
> Like mentioned above, HVC_SBI is useful for newer SOCs and boards
> where serial driver is not yet up-streamed.

Ok. Lets keep it then.

> Regards,
> Anup
>
> > Regards,
> > Atish
> > > Ideally "console=" kernel parameter passed by bootloaders should
> > > be the one selecting a preferred real console.
> > >
> > > This patch fixes above issue by not forcing RISCV SBI console as
> > > preferred console.
> > >
> > > Fixes: afa6b1ccfad5 ("tty: New RISC-V SBI console driver")
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
> > > ---
> > >    drivers/tty/hvc/hvc_riscv_sbi.c | 1 -
> > >    1 file changed, 1 deletion(-)
> > >
> > > diff --git a/drivers/tty/hvc/hvc_riscv_sbi.c b/drivers/tty/hvc/hvc_riscv_sbi.c
> > > index 75155bde2b88..31f53fa77e4a 100644
> > > --- a/drivers/tty/hvc/hvc_riscv_sbi.c
> > > +++ b/drivers/tty/hvc/hvc_riscv_sbi.c
> > > @@ -53,7 +53,6 @@ device_initcall(hvc_sbi_init);
> > >    static int __init hvc_sbi_console_init(void)
> > >    {
> > >        hvc_instantiate(0, 0, &hvc_sbi_ops);
> > > -     add_preferred_console("hvc", 0, NULL);
> > >
> > >        return 0;
> > >    }

Reviewed-by: Atish Patra <atish.patra@xxxxxxx>

Regards,
Atish