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

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Message-ID: <alpine.DEB.2.21.9999.1904291254300.7063@viisi.sifive.com>
Date:   Mon, 29 Apr 2019 13:02:21 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Anup Patel <anup@...infault.org>
cc:     Christoph Hellwig <hch@...radead.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Anup Patel <Anup.Patel@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jiri Slaby <jslaby@...e.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH] tty: Don't force RISCV SBI console as preferred
 console

On Fri, 26 Apr 2019, Anup Patel wrote:

> On Fri, Apr 26, 2019 at 11:51 AM Christoph Hellwig <hch@...radead.org> wrote:
> >
> > On Thu, Apr 25, 2019 at 09:41:21PM -0700, Atish Patra wrote:
> > > 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.
> >
> > I think the whole concept of the SBI console is a little dangerous.
> > It means that for one piece of physical hardware (usually the uart)
> > we have two entiries (the M-mode firmware and the OS) in control,
> > which tends to rarely end well.
> 
> I think the SBI console is only useful for early SOC bringup and early
> SOC debugging when most drivers are not available in upstream
> kernel. It cannot (and should not) be used in production deployments.

Usually the primary use-case for an abstract console interface is for 
desktop and server users.  Usually Linux distributions want a hardware 
platform-specific bootloader or BIOS to specify and control the console.  

Originally I suspect this was implemented in the SBI for semi-hosting 
purposes, but that's no longer really applicable.


- Paul