[PATCH 13/34] drm/amdgpu: Convert ctx_handles to XArray

[Matthew Wilcox]

On Mon, Feb 25, 2019 at 04:59:55PM +0000, Koenig, Christian wrote:
> Am 25.02.19 um 17:39 schrieb Matthew Wilcox:
> > On Mon, Feb 25, 2019 at 05:07:24PM +0100, Christian König wrote:
> >>> -#define AMDGPU_VM_MAX_NUM_CTX			4096
> >>> +#define AMDGPU_VM_CTX_LIMIT			XA_LIMIT(0, 4095)
> >> IIRC we actually use 0 as reserved context value in some places.
> > That's OK; the ALLOC1 prevents it from using index 0.
> >
> > You can change it to be XA_LIMIT(1, 4095) if you think that'll be clearer;
> > it'll be slightly less efficient assembly (a 64-bit mov-immediate instead
> > of a 32-bit mov-immediate), but it's your driver, so it's up to you.
> 
> A code comment should do as well.
> 
> But thinking more about it please DON'T actually change the 
> AMDGPU_VM_MAX_NUM_CTX define.
> 
> That one needs to be used to calculate the reserved GPU space to map the 
> context save area, and I really don't want to deal with a XA_LIMIT in 
> that calculation :)
> 
> I'm really wondering why that doesn't go up in a boom during compilation....

Maybe that code isn't merged in Linus' tree yet?  I was basing this on
5.0-rc5 and there's no mention of AMDGPU_VM_MAX_NUM_CTX outside these
usages.  If I'd seen another usage, I wouldn't've changed it.

The rebasing I'm going to have to do on -rc1 is going to be epically
challenging.