On Mon, 12 Apr 2021 at 16:17, Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Mon, Apr 12, 2021 at 10:05:25AM +0100, Matthew Auld wrote: > > We need to general our accessor for the page directories and tables from > > using the simple kmap_atomic to support local memory, and this setup > > must be done on acquisition of the backing storage prior to entering > > fence execution contexts. Here we replace the kmap with the object > > maping code that for simple single page shmemfs object will return a > > plain kmap, that is then kept for the lifetime of the page directory. > > > > v2: (Thomas) Rebase on dma_resv and obj->mm.lock removal. > > > > Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx> > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > So I wanted to understand what px stands for as an abbreviation, and dug > all the way down to this: > > commit 567047be2a7ede082d29f45524c287b87bd75e53 > Author: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> > Date: Thu Jun 25 18:35:12 2015 +0300 > > drm/i915/gtt: Use macros to access dma mapped pages > > I still have no idea what it means, I guess px = page. But I also > committed this, so I guess can blame myself :-) > > But while digging I've stumbled over this here > > commit 6eebfe8a10a62139d681e2f1af1386252742278b > Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Date: Fri Jul 12 08:58:18 2019 +0100 > > drm/i915/gtt: Use shallow dma pages for scratch > > > And that's some serious wtf. Yes we've done some compile-time type > casting automagic between i915_priv and dev in the past, and I think even > that was bad taste. But it was justified with that we have these > everywhere (especially in the mmio macros), and it would be a terrible > flag day. > > But I'm not seeing any need for auto-casting for these pages here, and I'm > not aware that we're doing this anywhere else in kernel code. There is > some macro-trickery in lockdep annotations, but that relies on the lockdep > map having the same struct member name in all lock types, and is not > exposed to drivers at all. > > Am I missing something, or why do we have this compile-time type casting > stuff going on in i915 page accessors? I think 'x' in the px family of macros/functions is meant in the variable/polymorphic sense, so it can potentially be a pt, pd, etc underneath. If you look at px_base() for example all it does is fish out the base GEM object from the structure, using the known-at-compile-time-type, which then lets us get at the dma address, vaddr etc. It does seem pretty magical, but seems ok to me, if it means less typing? _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
