Re: [PATCH 2/3] irqchip/gic: Use 0x10000 offset to access GICC_DIR on STM32MP2

[Christian Bruel <christian.bruel@foss.st.com>]

On 4/3/25 19:50, Marc Zyngier wrote:
> On Thu, 03 Apr 2025 13:28:04 +0100,
> Christian Bruel <christian.bruel@foss.st.com> wrote:
>>
>> When GIC_4KNOT64K bit in the GIC configuration register is
>> 0 (64KB), address block is modified in such a way than only the
>> first 4KB of the GIC cpu interface are accessible with default
>> offsets.
>> With this bit mapping GICC_DIR register is accessible at
>> offset 0x10000 instead of 0x1000, thus remap accordingly
> 
> And I'm pretty sure the whole of the GICC range is correctly
> accessible at offset 0xF000, giving you the full 8kB you need. That's
> because each page of the GIC is aliased over two 64kB blocks, as per
> the integration guidelines so that MMU isolation can be provided on a
> 64kB boundary.

Thanks a lot for this explanation, indeed this works like a charm.

> 
> Funnily enough, all it takes is to adjust GICC region. You can either:
> 
> - make it 128kB wide, and the driver will take care of it (details in
>    gic_check_eoimode()). On one of my boxes that is similarly
>    configured, I get:
> 
>    [    0.000000] NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0
>    [    0.000000] GIC: Adjusting CPU interface base to 0x00000000780af000
>    [    0.000000] Root IRQ handler: gic_handle_irq
>    [    0.000000] GIC: Using split EOI/Deactivate mode
> 
>    See below for what I expect to be the correct fix.
>    
> - make it 8kB wide from offset 0xF000.

I checked both and they work. I will go for the former to show real 8kB 
size to be exposed in the DT. And there are a few other platforms that
use this alias

> 
> Unless the ST HW folks have been even more creative, none of this
> overly complicated stuff should be necessary. Just describe the HW
> correctly.

I was unable to find this information in the GIC-400 trm 
(https://developer.arm.com/documentation/ddi0471/b/programmers-model/gic-400-register-map). 
Now I also prefer to use GICC alias at
offset 0xf000 as suggested rather than the quirk solution

thank you very much

Christian

> 
> 	M.
> 
> diff --git a/arch/arm64/boot/dts/st/stm32mp251.dtsi b/arch/arm64/boot/dts/st/stm32mp251.dtsi
> index f3c6cdfd7008..97b7a7106a02 100644
> --- a/arch/arm64/boot/dts/st/stm32mp251.dtsi
> +++ b/arch/arm64/boot/dts/st/stm32mp251.dtsi
> @@ -120,7 +120,7 @@ intc: interrupt-controller@4ac00000 {
>   		#address-cells = <1>;
>   		interrupt-controller;
>   		reg = <0x0 0x4ac10000 0x0 0x1000>,
> -		      <0x0 0x4ac20000 0x0 0x2000>,
> +		      <0x0 0x4ac20000 0x0 0x20000>,
>   		      <0x0 0x4ac40000 0x0 0x2000>,
>   		      <0x0 0x4ac60000 0x0 0x2000>;
>   	};
>