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

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Date:   Mon, 29 Apr 2019 12:50:42 -0700
From:   Atish Patra <atish.patra@....com>
To:     Anup Patel <anup@...infault.org>
Cc:     Anup Patel <Anup.Patel@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christoph Hellwig <hch@...radead.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] tty: Don't force RISCV SBI console as preferred console

On 4/25/19 11:21 PM, Anup Patel wrote:
> On Fri, Apr 26, 2019 at 10:11 AM Atish Patra <atish.patra@....com> 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@...r.kernel.org
>>> Signed-off-by: Anup Patel <anup.patel@....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;
>>>    }
>>>
>>
> 

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

Regards,
Atish