From mboxrd@z Thu Jan 1 00:00:00 1970 From: dave.martin@linaro.org (Dave Martin) Date: Mon, 20 Jun 2011 14:40:29 +0100 Subject: [PATCH 4/4] ARM: Documentation: clarify entry requirements for ARM versus Thumb-2 In-Reply-To: <1308577229-23681-1-git-send-email-dave.martin@linaro.org> References: <1308577229-23681-1-git-send-email-dave.martin@linaro.org> Message-ID: <1308577229-23681-5-git-send-email-dave.martin@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Currently, the kernel entry requirements are not explicit about whether the kernel should be entered in ARM or Thumb-2. Now that the boot protocol consistently requires the kernel Image or zImage to be entered in ARM state, document this requirement explicitly. A different rule will be needed for Cortex-M class CPUs as and when support for these lands upstream, since these CPUs don't support the ARM instruction set at all: a note is added to the effect that the kernel must be entered in Thumb on such systems. Signed-off-by: Dave Martin --- Documentation/arm/Booting | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-) diff --git a/Documentation/arm/Booting b/Documentation/arm/Booting index 4e686a2..a341d87 100644 --- a/Documentation/arm/Booting +++ b/Documentation/arm/Booting @@ -164,3 +164,8 @@ In either case, the following conditions must be met: - The boot loader is expected to call the kernel image by jumping directly to the first instruction of the kernel image. + On CPUs supporting the ARM instruction set, the entry must be + made in ARM state, even for a Thumb-2 kernel. + + On CPUs supporting only the Thumb instruction set such as + Cortex-M class CPUs, the entry must be made in Thumb state. -- 1.7.4.1