Re: [PATCH] perf/arm-cmn: don't claim resource during ioremap() for CMN700 with ACPI

[YinFengwei]

Add Jing Zhang as we will continue discussion in this thread.

On Tue, Feb 18, 2025 at 12:31:10PM +0800, Robin Murphy wrote:
> On 2025-02-18 10:58 am, YinFengwei wrote:
> > On Tue, Feb 18, 2025 at 10:31:42AM +0800, Robin Murphy wrote:
> > > On 2025-02-18 1:21 am, Yin Fengwei wrote:
> > > > Currently, arm-cmn PMU driver assumes ACPI claim resource
> > > > for CMN600 + ACPI. But with CMN700 + ACPI, the device probe
> > > > failed because of resource claim failes when ioremap() is
> > > > called:
> > > > [   10.837300] arm-cmn ARMHC700:00: error -EBUSY: can't request region for resource [mem 0x40000000-0x4fffffff]
> > > > [   10.847310] arm-cmn ARMHC700:00: probe with driver arm-cmn failed with error -16
> > > > [   10.854726] arm-cmn ARMHC700:02: error -EBUSY: can't request region for resource [mem 0x40040000000-0x4004fffffff]
> > > > [   10.865085] arm-cmn ARMHC700:02: probe with driver arm-cmn failed with error -16
> > > > 
> > > > Let CMN700 + ACPI do same as CMN600 + ACPI to allow CMN700
> > > > work in ACPI env.
> > > 
> > > No, the CMN-600 routine is a special case for CMN-600 having two nested
> > > memory resources of its own. CMN-700 and everything else only have one
> > > memory resource, so that is not appropriate. What else is claiming the
> > > region to cause a conflict?
> > Sorry. Forgot the link for the new proposed fix:
> > https://lore.kernel.org/all/Z7QYlUP6nfBNMXsv@U-V2QX163P-2032.local/
> 
> Yes, I saw that. It's a broken diff that won't even compile, with no
> explanation of what it's supposed to be trying to achieve or why. I'm not
> sure what you're asking me to comment on.
My bad. I will attatch the full patch at the end of this mail.

> 
> > My understanding is that there are two problems here:
> > 1. ACPI claim the memory range and that's why we see this -EBUSY error
> >     with correct code path for CMN700 + ACPI table.
> 
> No, it's fine to claim the exact *same* range that the ACPI companion owns;
> the identical requests just nest inside each other. I don't have a CMN-700
> to hand but here's a selection of other drivers doing just that from
> /proc/iomem on my system:
> 
> 12600000-12600fff : ARMH0011:00
>   12600000-12600fff : ARMH0011:00 ARMH0011:00
> 12610000-12610fff : ARMH0011:01
>   12610000-12610fff : ARMH0011:01 ARMH0011:01
> 126b0000-126b0fff : APMC0D0F:00
>   126b0000-126b0fff : APMC0D0F:00 APMC0D0F:00
> 126f0000-126f0fff : APMC0D81:00
>   126f0000-126f0fff : APMC0D81:00 APMC0D81:00
I believe this works only for parents/children resource node. Otherwise,
there will be conflict.

> 
> And I know people are using the CMN-700 PMU on other ACPI systems without
> issue, so there's nothing wrong with the binding or the driver in general.
> 
> The resource conflict only arises when a request overlaps an existing region
> inexactly. Either your firmware is describing the CMN incorrectly, or some
> other driver is claiming conflicting iomem regions for some reason.
No. It's not ACPI table problem. The problem is mentioned in comments of
function arm_cmn600_acpi_probe():
        /*
         * Note that devm_ioremap_resource() is dumb and won't let the platform
         * device claim cfg when the ACPI companion device has already claimed
         * root within it. But since they *are* already both claimed in the
         * appropriate name, we don't really need to do it again here anyway.
         */

So I suppose for ACPI env, we should use devm_ioremap() as cmn600 does.
And make CMN700 handling follow spec exactly.
> 
> Thanks,
> Robin.

Regards
Yin, Fengwei

Full patch here (base commit is: 2408a807bfc3f738850ef5ad5e3fd59d66168996):