[RFC PATCH v4 03/18] Documentation: devicetree: arm: cpus/cpu nodes bindings updates
Lorenzo Pieralisi
lorenzo.pieralisi at arm.com
Mon Jul 15 05:34:06 EDT 2013
On Fri, Jul 12, 2013 at 03:47:17PM +0100, Rob Herring wrote:
> On Fri, May 17, 2013 at 10:20 AM, Lorenzo Pieralisi
> <lorenzo.pieralisi at arm.com> wrote:
> > In order to extend the current cpu nodes bindings to newer CPUs
> > inclusive of AArch64 and to update support for older ARM CPUs this
> > patch updates device tree documentation for the cpu nodes bindings.
>
> Sorry for the long delay on this, but I'm still not happy with the binding here.
I had to ask Russell again to drop the bindings patches from the patch
system, and this is not acceptable since two months have passed and the
entire series was reviewed, acked and partially merged. I will review
these bindings again but I would like to understand who should give the final
go ahead to get these patches queued for upstreaming, I can't continue
updating this stuff forever.
> > Main changes:
> > - adds 64-bit bindings
> > - define usage of #address-cells
> > - define 32/64 dts compatibility settings
> > - defines behaviour on pre and post v7 uniprocessor systems
> > - adds ARM 11MPcore specific reg property definition
> >
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> > ---
> > Documentation/devicetree/bindings/arm/cpus.txt | 459 ++++++++++++++++++++++---
> > 1 file changed, 412 insertions(+), 47 deletions(-)
>
> [snip]
>
> > + # On ARM v8 64-bit systems, where the reg property
> > + size can be 1 or 2 cells (as defined by cpus node's
> > + #address-cells property), this property is
> > + required and matches:
> > +
> > + - On systems running the OS in AArch32:
>
> The DTS cannot change based on 32-bit or 64-bit OS.
"On systems running the OS in AArch32" implies a dependency on the
HW execution state. Since the DT is used to configure OSs I thought that
could be a valid sentence. Unfortunately this stuff is not C, so I
reiterate my point above, before changing it I would like to understand
who should say the wording is ok otherwise we could argue forever.
> > +
> > + * If the cpus node's #address-cells value is 2:
> > +
> > + The first reg cell must be set to 0.
> > +
> > + The second reg cell bits [23:0] must be set to
> > + bits [23:0] of MPIDR_EL1.
> > +
> > + All other bits in the reg cells must be set to 0.
> > +
> > + * If the cpus node's #address-cells value is 1:
> > +
> > + Bits [23:0] in the reg cell must be set to
> > + bits [23:0] in MPIDR_EL1.
> > +
> > + All other bits in the reg cell must be 0.
> > +
> > + - On systems running the OS in AArch64:
> > +
> > + * If the cpus node's #address-cells value is 2:
> > +
> > + The first reg cell bits [7:0] must be set to
> > + bits [39:32] of MPIDR_EL1.
> > +
> > + The second reg cell bits [23:0] must be set to
> > + bits [23:0] of MPIDR_EL1.
> > +
> > + All other bits in the reg cells must be set to 0.
> > +
> > + * If the cpus node's #address-cells value is 1:
> > +
> > + MPIDR_EL1[63:32] is 0 on all processors in the
> > + system.
>
> Your logic is backwards here. If the MPIDR_EL1[63:32] is 0, then
> #address-cells can be 1. You could say the upper bits are ignored and
> treated as 0. However, you should simplify all this and just mandate
> that #address-cells must be 2 for ARMv8 or more generally must match
> the size of the MPIDR. If we want to boot a 32-bit kernel, then the
> kernel will have to adapt to support this.
Fair enough I will see how I can reword it.
> > +
> > + The reg cell bits [23:0] must be set to
> > + bits [23:0] of MPIDR_EL1.
> > +
> > + All other bits in the reg cell must be set to 0.
> > +
> > + - compatible:
> > + Usage: required
> > + Value type: <string>
> > + Definition: should be one of:
> > + "arm,arm710t"
> > + "arm,arm720t"
> > + "arm,arm740t"
> > + "arm,arm7ej-s"
> > + "arm,arm7tdmi"
> > + "arm,arm7tdmi-s"
> > + "arm,arm9es"
> > + "arm,arm9ej-s"
> > + "arm,arm920t"
> > + "arm,arm922t"
> > + "arm,arm925"
> > + "arm,arm926e-s"
> > + "arm,arm926ej-s"
> > + "arm,arm940t"
> > + "arm,arm946e-s"
> > + "arm,arm966e-s"
> > + "arm,arm968e-s"
> > + "arm,arm9tdmi"
> > + "arm,arm1020e"
> > + "arm,arm1020t"
> > + "arm,arm1022e"
> > + "arm,arm1026ej-s"
> > + "arm,arm1136j-s"
> > + "arm,arm1136jf-s"
> > + "arm,arm1156t2-s"
> > + "arm,arm1156t2f-s"
> > + "arm,arm1176jzf"
> > + "arm,arm1176jz-s"
> > + "arm,arm1176jzf-s"
> > + "arm,arm11mpcore"
> > + "arm,cortex-a5"
> > + "arm,cortex-a7"
> > + "arm,cortex-a8"
> > + "arm,cortex-a9"
> > + "arm,cortex-a15"
> > + "arm,cortex-a53"
> > + "arm,cortex-a57"
> > + "arm,cortex-m0"
> > + "arm,cortex-m0+"
> > + "arm,cortex-m1"
> > + "arm,cortex-m3"
> > + "arm,cortex-m4"
> > + "arm,cortex-r4"
> > + "arm,cortex-r5"
> > + "arm,cortex-r7"
> > + "faraday,fa526"
> > + "intel,sa110"
> > + "intel,sa1100"
> > + "marvell,feroceon"
> > + "marvell,mohawk"
> > + "marvell,pj4"
> > + "marvell,sheeva-v7"
> > + "marvell,xsc3"
> > + "marvell,xscale"
> > + "qcom,krait"
> > + "qcom,scorpion"
> > + - enable-method
> > + Value type: <stringlist>
> > + Usage and definition depend on ARM architecture version and
> > + configuration:
> > + # On ARM v8 64-bit systems running the OS in AArch64,
>
> Again, the DTS can't depend on the OS type.
It was meant to make it dependent on the execution state.
> > + this property is required and must be one of:
> > + "spin-table"
> > + "psci"
> > + # On ARM 32-bit systems or ARM v8 systems running
> > + the OS in AArch32 this property is prohibited.
>
> I still don't get the distinction between 32 and 64 bit here. On
> 32-bit, you have 3 choices: psci, spin-table, or SoC specific. So make
> this property optional for 32-bit and mandatory for 64-bit.
Ok.
> > +
> > + - cpu-release-addr
> > + Usage: required for systems that have an "enable-method"
> > + property value of "spin-table".
> > + Value type: <prop-encoded-array>
> > + Definition:
> > + # On ARM v8 64-bit systems must be a two cell
> > + property identifying a 64-bit zero-initialised
> > + memory location.
>
> As I mentioned previously, isn't some wake-up method needed? Most
> systems will be in wfi or wfe rather than continuously spinning.
Mmm...this can become a minefield, wfe, wfi, CPU in reset..this needs some
thought.
Thanks,
Lorenzo
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