[PATCH 3/5] drm/xe: Helper to get dpa from pfn

[Zeng, Oak]

> -----Original Message-----
> From: Brost, Matthew <matthew.brost at intel.com>
> Sent: Thursday, March 14, 2024 1:39 PM
> To: Zeng, Oak <oak.zeng at intel.com>
> Cc: intel-xe at lists.freedesktop.org; Hellstrom, Thomas
> <thomas.hellstrom at intel.com>; airlied at gmail.com; Welty, Brian
> <brian.welty at intel.com>; Ghimiray, Himal Prasad
> <himal.prasad.ghimiray at intel.com>
> Subject: Re: [PATCH 3/5] drm/xe: Helper to get dpa from pfn
> 
> On Wed, Mar 13, 2024 at 11:35:51PM -0400, Oak Zeng wrote:
> > Since we now create struct page backing for each vram page,
> > each vram page now also has a pfn, just like system memory.
> > This allow us to calcuate device physical address from pfn.
> >
> > Signed-off-by: Oak Zeng <oak.zeng at intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_device_types.h | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/xe/xe_device_types.h
> b/drivers/gpu/drm/xe/xe_device_types.h
> > index bbea40b57e84..bf349321f037 100644
> > --- a/drivers/gpu/drm/xe/xe_device_types.h
> > +++ b/drivers/gpu/drm/xe/xe_device_types.h
> > @@ -576,4 +576,12 @@ static inline struct xe_tile *mem_region_to_tile(struct
> xe_mem_region *mr)
> >  	return container_of(mr, struct xe_tile, mem.vram);
> >  }
> >
> > +static inline u64 vram_pfn_to_dpa(struct xe_mem_region *mr, u64 pfn)
> > +{
> > +	u64 dpa;
> > +	u64 offset = (pfn << PAGE_SHIFT) - mr->hpa_base;
> 
> Can't this be negative?
> 
> e.g. if pfn == 0, offset == -mr->hpa_base.
> 
> Or is the assumption (pfn << PAGE_SHIFT) is always > mr->hpa_base?
> 
> If so can we an assert or something to ensure we using this function correctly.

Yes we can assert it. The hpa_base is the host physical base address for this memory region, while pfn should point to a page inside this memory region.

I will add an assertion.


> 
> > +	dpa = mr->dpa_base + offset;
> > +	return dpa;
> > +}
> 
> Same as previous patch, should be *.h not a *_types.h file.

Yes will fix.
> 
> Also as this is xe_mem_region not explictly vram. Maybe:
> 
> s/vram_pfn_to_dpa/xe_mem_region_pfn_to_dpa/

Xe_mem_region can only represent vram, right? I mean it can't represent system memory. Copied the definition below:

/**
 * struct xe_mem_region - memory region structure
 * This is used to describe a memory region in xe
 * device, such as HBM memory or CXL extension memory.
 */

Oak

> 
> Matt
> 
> > +
> >  #endif
> > --
> > 2.26.3
> >