linux-kernel - [PATCH] tty: hvc: Don't enable the RISC-V SBI console by default

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Date: Wed, 14 Feb 2024 07:34:30 -0800
From: Palmer Dabbelt <palmer@...osinc.com>
To:         linux-riscv@...ts.infradead.org
Cc: Greg KH <gregkh@...uxfoundation.org>, jirislaby@...nel.org,
  Palmer Dabbelt <palmer@...osinc.com>, Atish Patra <atishp@...osinc.com>, ajones@...tanamicro.com,
  apatel@...tanamicro.com, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
  linux-serial@...r.kernel.org, Emil Renner Berthing <kernel@...il.dk>
Subject: [PATCH] tty: hvc: Don't enable the RISC-V SBI console by default

From: Palmer Dabbelt <palmer@...osinc.com>

The new SBI console has the same problem as the old one: there's only
one shared backing hardware and no synchronization, so the two drivers
end up stepping on each other.  This was the same issue the old SBI-0.1
console drivers had, but that was disabled by default when SBI-0.1 was.

So just mark the new driver as nonportable.

Reported-by: Emil Renner Berthing <kernel@...il.dk>
Fixes: 88ead68e764c ("tty: Add SBI debug console support to HVC SBI driver")
Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
---
 drivers/tty/hvc/Kconfig | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index 6e05c5c7bca1..c2a4e88b328f 100644
--- a/drivers/tty/hvc/Kconfig
+++ b/drivers/tty/hvc/Kconfig
@@ -108,13 +108,15 @@ config HVC_DCC_SERIALIZE_SMP
 
 config HVC_RISCV_SBI
 	bool "RISC-V SBI console support"
-	depends on RISCV_SBI
+	depends on RISCV_SBI && NONPORTABLE
 	select HVC_DRIVER
 	help
 	  This enables support for console output via RISC-V SBI calls, which
-	  is normally used only during boot to output printk.
+	  is normally used only during boot to output printk.  This driver
+	  conflicts with real console drivers and should not be enabled on
+	  systems that directly access the console.
 
-	  If you don't know what do to here, say Y.
+	  If you don't know what do to here, say N.
 
 config HVCS
 	tristate "IBM Hypervisor Virtual Console Server support"
-- 
2.43.0