From: u.kleine-koenig@pengutronix.de (Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=) Date: Sun, 28 Sep 2014 12:18:46 +0200 Subject: [PATCH v4] ARM: zImage: add support for ARMv7-M In-Reply-To: <1411817149-5135-1-git-send-email-manabian@gmail.com> References: <1411057343-20861-1-git-send-email-manabian@gmail.com> <1411817149-5135-1-git-send-email-manabian@gmail.com> Message-ID: <20140928101846.GE31554@pengutronix.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hello Joachim, On Sat, Sep 27, 2014 at 01:25:49PM +0200, Joachim Eastwood wrote: > This patch makes it possible to enter zImage in Thumb mode for ARMv7M The official spelling is ARMv7-M. > (Cortex-M) CPUs that does not support ARM mode. The kernel entry is > also made in Thumb mode. > > Signed-off-by: Joachim Eastwood > --- > Hi, > > Updated patch with comments from Uwe Kleine-K?nig. > > Changes > v4: Preserve r1/r2. Add comment about class A/R. > v3: Use defines for ARMv7M CPU registers. > v2: Introduce AR_CLASS/M_CLASS macros. This reduces the amount > of ifdefs needed in compressed/head.S. > > Successfully tested on NXP LPC4357 (Cortex-M4). > > regards, > Joachim Eastwood > > arch/arm/boot/compressed/head.S | 28 ++++++++++++++++++++++------ > arch/arm/include/asm/unified.h | 8 ++++++++ > 2 files changed, 30 insertions(+), 6 deletions(-) > > diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S > index 413fd94b5301..0afcbb1e1d7d 100644 > --- a/arch/arm/boot/compressed/head.S > +++ b/arch/arm/boot/compressed/head.S > @@ -10,8 +10,11 @@ > */ > #include > #include > +#include > + > + AR_CLASS( .arch armv7-a ) > + M_CLASS( .arch armv7-m ) > > - .arch armv7-a > /* > * Debugging stuff > * > @@ -114,7 +117,12 @@ > * sort out different calling conventions > */ > .align > - .arm @ Always enter in ARM state > + /* > + * Always enter in ARM state for CPUs that support the ARM ISA. > + * As of today (2014) that's exactly the members of the A and R > + * classes. > + */ > + AR_CLASS( .arm ) > start: > .type start,#function > .rept 7 > @@ -132,14 +140,15 @@ start: > > THUMB( .thumb ) > 1: > - ARM_BE8( setend be ) @ go BE8 if compiled for BE8 > - mrs r9, cpsr > + ARM_BE8( setend be ) @ go BE8 if compiled for BE8 > + AR_CLASS( mrs r9, cpsr ) > #ifdef CONFIG_ARM_VIRT_EXT > bl __hyp_stub_install @ get into SVC mode, reversibly > #endif > mov r7, r1 @ save architecture ID > mov r8, r2 @ save atags pointer > > +#ifndef CONFIG_CPU_V7M > /* > * Booting from Angel - need to enter SVC mode and disable > * FIQs/IRQs (numeric definitions from angel arm.h source). > @@ -155,6 +164,7 @@ not_angel: > safe_svcmode_maskall r0 > msr spsr_cxsf, r9 @ Save the CPU boot mode in > @ SPSR > +#endif > /* > * Note that some cache flushing and other stuff may > * be needed here - is there an Angel SWI call for this? > @@ -790,6 +800,9 @@ __common_mmu_cache_on: > call_cache_fn: adr r12, proc_types > #ifdef CONFIG_CPU_CP15 > mrc p15, 0, r9, c0, c0 @ get processor ID > +#elif defined(CONFIG_CPU_V7M) > + ldr r9, =BASEADDR_V7M_SCB > + ldr r9, [r9, V7M_SCB_CPUID] > #else > ldr r9, =CONFIG_PROCESSOR_ID > #endif > @@ -945,11 +958,13 @@ proc_types: > W(b) __armv4_mmu_cache_off > W(b) __armv6_mmu_cache_flush > > +#ifndef CONFIG_CPU_V7M > .word 0x000f0000 @ new CPU Id > .word 0x000f0000 > W(b) __armv7_mmu_cache_on > W(b) __armv7_mmu_cache_off > W(b) __armv7_mmu_cache_flush > +#endif this #ifndef is needed because it is matched for V7-M CPU, but __armv7_mmu_cache_\* is wrong for these, right? So I suggest adding a comment here, something like: /* * v7-M CPUs match this entry, but the cache handling is * different to v7-A and v7-R. So this entry has to be * skipped for v7-M builds. */ Alternatives are: - Find a way to differentiate the AR and M classes. I think you cannot by just looking at the CPU ID value, so the selection of the right functions would need to become more (compl|sophist)icated. - As there is no v7-M cache architecurally defined, return early in the #elif branch above (line 803). I think the first option isn't practicable. The second is IMHO a nice alternative. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-K?nig | Industrial Linux Solutions | http://www.pengutronix.de/ |