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

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Mar 15, 2024 at 11:29:33AM -0600, Zeng, Oak wrote:
> 
> 
> > -----Original Message-----
> > From: Brost, Matthew <matthew.brost@intel.com>
> > Sent: Thursday, March 14, 2024 1:39 PM
> > To: Zeng, Oak <oak.zeng@intel.com>
> > Cc: intel-xe@lists.freedesktop.org; Hellstrom, Thomas
> > <thomas.hellstrom@intel.com>; airlied@gmail.com; Welty, Brian
> > <brian.welty@intel.com>; Ghimiray, Himal Prasad
> > <himal.prasad.ghimiray@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@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.
>  */
> 

Ah yes but still as the first argument is xe_mem_region I think the
function name should reflect that.

Matt

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