On 1 June 2015 at 23:45, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Mon, Jun 01, 2015 at 01:22:00PM -0700, Stephen Boyd wrote: >> The standard boot protocol on ARM requires CPUs to be entered in >> the ARM state, unless they don't support the ARM instruction set >> (see Documentation/arm/Booting). On THUMB2 kernels, we assume >> the firmware can determine what state to enter the kernel in, but >> some firmwares don't honor the thumb bit. Make the cpu_resume >> symbol an ARM symbol, so that firmwares that honor the thumb bit >> will enter the kernel in ARM state and firmwares that don't honor >> the thumb bit will be able to enter the kernel in ARM state >> without more changes. >> >> This fixes a problem reported by Kevin Hilman where the ifc6410 >> fails to boot for THUMB2 kernels because the platform's firmware >> always enters the kernel in ARM mode from deep idle states. > > Please do this differently. The default should be (as we do with > the SMP secondary entry path) to assume that the firmware does the > right thing. > > So, if we want an ARM-mode entry point, please use: > > + .arm > +ENTRY(cpu_resume_arm) > + THUMB( badr r9, 1f ) @ Kernel is entered in ARM. > + THUMB( bx r9 ) @ If this is a Thumb-2 kernel, > + THUMB( .thumb ) @ switch to Thumb now. > + THUMB(1: ) > > Don't forget an ENDPROC() for the new symbol. Buggy platforms then > use cpu_resume_arm instead of cpu_resume. > OK, I think that was Stephen intention at first, but I suggested this instead. The point is that it is safer and more tidy to make these entry points ARM only throughout, and switch to Thumb2 only if THUMB2_KERNEL. This way, since all firmwares (except ARMv7-M, but let's disregard that for now) are known to be able to enter/resume into the kernel in ARM mode, this is more robust in the face of new platforms and firmware revisions of existing platforms. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
