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[2a02:3100:a56c:5c01:55c4:777b:77ab:69e3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4954966a033sm30243855e9.0.2026.07.17.02.44.06 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 17 Jul 2026 02:44:07 -0700 (PDT) From: Karl Mehltretter To: Greg Kroah-Hartman , Jiri Slaby Cc: Arnd Bergmann , Nicolas Pitre , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Karl Mehltretter Subject: [PATCH v2] tty: hvc: restrict HVC_DCC to ARMv6+ and ARM64 Date: Fri, 17 Jul 2026 11:44:00 +0200 Message-Id: <20260717094400.67501-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit hvc_dcc drives the JTAG DCC via the ARMv6/v7 CP14 debug registers (mrc/mcr p14, 0, rX, c0, c1/c5, 0 in asm/dcc.h). That encoding is undefined on older ARM cores, and also on ARMv7-M, but HVC_DCC only depends on ARM, so it can be enabled on e.g. ARM926 (ARCH_MULTI_V5), where hvc_dcc_console_init() runs __dcc_putchar() at boot and takes an undefined-instruction trap before the console is up: Internal error: Oops - undefined instruction: 0 [#1] ARM PC is at hvc_dcc_check+0x50/0x8c hvc_dcc_check from hvc_dcc_console_init+0x18/0x48 hvc_dcc_console_init from console_init+0x58/0x170 Kernel panic - not syncing: Fatal exception Restrict HVC_DCC to the CPUs where that encoding is valid: the CPU_V6 || CPU_V6K || CPU_V7 set that arch/arm/include/debug/icedcc.S guards it with, plus ARM64. COMPILE_TEST keeps the driver buildable on the excluded cores, where the p14 encodings still assemble. Fixes: 16c63f8ea49c ("drivers: char: hvc: add arm JTAG DCC console support") Signed-off-by: Karl Mehltretter --- v2: add COMPILE_TEST to keep arm build coverage, per Greg's comment drivers/tty/hvc/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig index c2a4e88b328f..51320f2f9a3f 100644 --- a/drivers/tty/hvc/Kconfig +++ b/drivers/tty/hvc/Kconfig @@ -79,7 +79,7 @@ config HVC_UDBG config HVC_DCC bool "ARM JTAG DCC console" - depends on ARM || ARM64 + depends on (ARM && (CPU_V6 || CPU_V6K || CPU_V7 || COMPILE_TEST)) || ARM64 select HVC_DRIVER select SERIAL_CORE_CONSOLE help -- 2.39.5 (Apple Git-154)