[PATCH] powerpc: Document xive=off option

[Cédric Le Goater]

On 5/13/19 7:39 AM, Michael Neuling wrote:
> commit 243e25112d06 ("powerpc/xive: Native exploitation of the XIVE
> interrupt controller") added an option to turn off Linux native XIVE
> usage via the xive=off kernel command line option.
> 
> This documents this option.
> 
> Signed-off-by: Michael Neuling <mikey at neuling.org>



Reviewed-by: Cédric Le Goater <clg at kaod.org>


But,

We should fix the behavior because xive=off does not work on pseries. 
This is not handled correctly in prom when CAS negotiates with the 
hypervisor which interrupt mode is to be used. 

I haven't tried this option on PowerNV.

Cheers,

C.


> ---
>  Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index c45a19d654..ee410d0ef4 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5177,6 +5177,15 @@
>  			Format:
>  			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
>  
> +	xive=		[PPC]
> +			By default on POWER9 and above, the kernel will
> +			natively use the XIVE interrupt controller. This option
> +			allows the fallback firmware mode to be used:
> +
> +			off       Fallback to firmware control of XIVE interrupt
> +				  controller on both pseries and powernv
> +				  platforms. Only useful on POWER9 and above.
> +
>  	xhci-hcd.quirks		[USB,KNL]
>  			A hex value specifying bitmask with supplemental xhci
>  			host controller quirks. Meaning of each bit can be
>