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Subject: Re: [PATCH] tty: Don't force RISCV SBI console as preferred console
To:     Anup Patel <Anup.Patel@wdc.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>
Cc:     Christoph Hellwig <hch@infradead.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
References: <20190425133435.56065-1-anup.patel@wdc.com>
From:   Atish Patra <atish.patra@wdc.com>
Message-ID: <9a8be7ef-e62e-2a93-9170-e3dc70dfb25f@wdc.com>
Date:   Thu, 25 Apr 2019 21:41:21 -0700
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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.

If we don't need it, I suggest we should remove the config option from 
defconfig in addition to this patch.

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@vger.kernel.org
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> ---
>   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;
>   }
>