RE: [RFC 5/5] powerpc/fsl: Add supported-irq-ranges for P2020

[Bharat Bhushan]

> -----Original Message-----
> From: Scott Wood [mailto:oss@xxxxxxxxxxxx]
> Sent: Wednesday, August 8, 2018 11:27 PM
> To: Bharat Bhushan <bharat.bhushan@xxxxxxx>;
> benh@xxxxxxxxxxxxxxxxxxx; paulus@xxxxxxxxx; mpe@xxxxxxxxxxxxxx;
> galak@xxxxxxxxxxxxxxxxxxx; mark.rutland@xxxxxxx;
> kstewart@xxxxxxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Cc: robh@xxxxxxxxxx; keescook@xxxxxxxxxxxx; tyreld@xxxxxxxxxxxxxxxxxx;
> joe@xxxxxxxxxxx
> Subject: Re: [RFC 5/5] powerpc/fsl: Add supported-irq-ranges for P2020
> 
> On Wed, 2018-08-08 at 06:28 +0000, Bharat Bhushan wrote:
> > > -----Original Message-----
> > > From: Scott Wood [mailto:oss@xxxxxxxxxxxx]
> > > Sent: Wednesday, August 8, 2018 11:26 AM
> > > To: Bharat Bhushan <bharat.bhushan@xxxxxxx>;
> > > benh@xxxxxxxxxxxxxxxxxxx; paulus@xxxxxxxxx; mpe@xxxxxxxxxxxxxx;
> > > galak@xxxxxxxxxxxxxxxxxxx; mark.rutland@xxxxxxx;
> > > kstewart@xxxxxxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx;
> > > devicetree@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; linux-
> > > kernel@xxxxxxxxxxxxxxx
> > > Cc: robh@xxxxxxxxxx; keescook@xxxxxxxxxxxx;
> > > tyreld@xxxxxxxxxxxxxxxxxx; joe@xxxxxxxxxxx
> > > Subject: Re: [RFC 5/5] powerpc/fsl: Add supported-irq-ranges for
> > > P2020
> > >
> > > On Wed, 2018-08-08 at 03:44 +0000, Bharat Bhushan wrote:
> > > > > -----Original Message-----
> > > > > From: Scott Wood [mailto:oss@xxxxxxxxxxxx]
> > > > > Sent: Wednesday, August 8, 2018 2:44 AM
> > > > > To: Bharat Bhushan <bharat.bhushan@xxxxxxx>;
> > > > > benh@xxxxxxxxxxxxxxxxxxx; paulus@xxxxxxxxx; mpe@xxxxxxxxxxxxxx;
> > > > > galak@xxxxxxxxxxxxxxxxxxx; mark.rutland@xxxxxxx;
> > > > > kstewart@xxxxxxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx;
> > > > > devicetree@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> > > > > linux- kernel@xxxxxxxxxxxxxxx
> > > > > Cc: robh@xxxxxxxxxx; keescook@xxxxxxxxxxxx;
> > > > > tyreld@xxxxxxxxxxxxxxxxxx; joe@xxxxxxxxxxx
> > > > > Subject: Re: [RFC 5/5] powerpc/fsl: Add supported-irq-ranges for
> > > > > P2020
> > > > >
> > > > > On Fri, 2018-07-27 at 15:18 +0530, Bharat Bhushan wrote:
> > > > > > MPIC on NXP (Freescale) P2020 supports following irq
> > > > > > ranges:
> > > > > >   > 0 - 11      (External interrupt)
> > > > > >   > 16 - 79     (Internal interrupt)
> > > > > >   > 176 - 183   (Messaging interrupt)
> > > > > >   > 224 - 231   (Shared message signaled interrupt)
> > > > >
> > > > > Why don't you convert to the 4-cell interrupt specifiers that
> > > > > make dealing with these ranges less error-prone?
> > > >
> > > > Ok , will do if we agree to have this series as per comment on
> > > > other patch.
> > >
> > > If you're concerned with errors, this would be a good things to do
> > > regardless.
> > >  Actually, it seems that p2020si-post.dtsi already uses 4-cell interrupts.
> > >
> > > What is motivating this patchset?  Is there something wrong in the
> > > existing dts files?
> >
> > There is no error in device tree. Main motivation is to improve code
> > for following reasons:
> >   - While code study it was found that if a reserved irq-number used
> > then there are no check in driver. irq will be configured as correct
> > and interrupt will never fire.
> 
> Again, a wrong interrupt number won't fire, whether an interrupt by that
> number exists or not.  I wouldn't mind a sanity check in the driver if the
> programming model made it properly discoverable, but I don't think it's
> worth messing with device trees just for this (and even less so given that
> there don't seem to be new chips coming out that this would be relevant
> for).

Fair enough, we can use MPIC version to define supported interrupts ranges. Will that be acceptable.

Thanks
-Bharat

> 
> > > > One other confusing observation I have is that "irq_count" from
> > > > platform code is given precedence over "last-interrupt-source" in
> > > > device-
> > >
> > > tree.
> > > > Should not device-tree should have precedence otherwise there is
> > > > no point using " last-interrupt-source" if platform code passes
> > > > "irq_count" in mpic_alloc().
> > >
> > > Maybe, though I don't think it matters much given that
> > > last-interrupt- source was only added to avoid having to pass
> > > irq_count in platform code.
> >
> > Thanks for clarifying;
> >
> > My understanding was that "last-interrupt-source" added to ensure that
> > we can over-ride value passed from platform code. In that case we do
> > not need to change code and can control from device tree.
> 
> The changelog says, "To avoid needing to write custom board-specific code
> to detect that scenario, allow it to be easily overridden in the device-tree,"
> where "it" means the value provided by hardware.  The goal was to pass in
> 256 without board code in the kernel, not to override the 256.
> 
> -Scott