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

[Zeng, Oak]

> -----Original Message-----
> From: Hellstrom, Thomas <thomas.hellstrom at intel.com>
> Sent: Monday, March 18, 2024 8:10 AM
> To: Brost, Matthew <matthew.brost at intel.com>; Zeng, Oak
> <oak.zeng at intel.com>
> Cc: intel-xe at lists.freedesktop.org; Welty, Brian <brian.welty at intel.com>;
> airlied at gmail.com; Ghimiray, Himal Prasad <himal.prasad.ghimiray at intel.com>
> Subject: Re: [PATCH 3/5] drm/xe: Helper to get dpa from pfn
> 
> On Thu, 2024-03-14 at 17:39 +0000, Matthew Brost wrote:
> > 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.
> 
> Please use imperative language according to the patch guidelines:
> Something like "Add a" or "Introduce A"
> 
> > >
> > > 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)
> 
> static inline header functions also need kerneldoc unless strong
> reasons not to.

Good point. Will document it.

Oak

> 
> /Thomas
> 
> 
> 
> > > +{
> > > +	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.
> >
> > > +	dpa = mr->dpa_base + offset;
> > > +	return dpa;
> > > +}
> >
> > Same as previous patch, should be *.h not a *_types.h file.
> >
> > Also as this is xe_mem_region not explictly vram. Maybe:
> >
> > s/vram_pfn_to_dpa/xe_mem_region_pfn_to_dpa/
> >
> > Matt
> >
> > > +
> > >  #endif
> > > --
> > > 2.26.3
> > >