On 2 June 2015 at 10:34, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Tue, Jun 02, 2015 at 08:18:18AM +0200, Ard Biesheuvel wrote: >> On 1 June 2015 at 23:45, Russell King - ARM Linux >> <linux@xxxxxxxxxxxxxxxx> wrote: >> > 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. > > Stop creating random interfaces with differing ways to call them. > Consistency is one of the important things. > Consistency was actually the point of my suggestion, but I see how the pre-existence of secondary_startup_arm() and your point regarding treating broken firmware as the exception may lead to the opposite conclusion. > We have three interfaces to the kernel: > > - Boot > - Secondary CPU > - Resume > > Out of those three, boot is the special one, as we have no way to > communicate what mode it is required - so we specify a mode, which > is ARM mode, except for CPUs which have no ARM mode support. > > Secondary CPU is not defined in the booting document because it's > not relevant, and it's not relevant for the same reason that the > resume entry point isn't. These entry points are not at a fixed > location in the kernel image, and the kernel has to communicate that, > along with their entry mode to the firmware. > > Therefore, firmware _does_ have the information to discover whether > the address should be called in ARM or Thumb mode, and what's more, > it should just work on those platforms which have no ARM mode support. > > If we start forcing these interfaces to be ARM mode only, we then need > the same work-arounds for them as for the boot interface. > > In other words, boot has a _valid_ reason to be different, the other > two are very similar in how they should be called. > > Besides, I'm not pandering to broken firmware. We should do the right > thing by default, which is to have sane interfaces, and only work around > stuff where needed. > > -- > FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up > according to speedtest.net. -- 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
