Received-SPF: pass (google.com: domain of linux-kernel+bounces-65436-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Subject: [PATCH] tty: hvc: Don't enable the RISC-V SBI console by default
Date: Wed, 14 Feb 2024 07:34:30 -0800
Message-ID: <20240214153429.16484-2-palmer@rivosinc.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Cc: Greg KH <gregkh@linuxfoundation.org>, jirislaby@kernel.org,
  Palmer Dabbelt <palmer@rivosinc.com>, Atish Patra <atishp@rivosinc.com>, ajones@ventanamicro.com,
  apatel@ventanamicro.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
  linux-serial@vger.kernel.org, Emil Renner Berthing <kernel@esmil.dk>
From: Palmer Dabbelt <palmer@rivosinc.com>
To:         linux-riscv@lists.infradead.org

From: Palmer Dabbelt <palmer@rivosinc.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@esmil.dk>
Fixes: 88ead68e764c ("tty: Add SBI debug console support to HVC SBI driver")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.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