Re: [PATCH 01/13] drm/exynos: Stop using frame_vector helpers

[John Hubbard]

On 10/7/20 2:32 PM, Daniel Vetter wrote:
> On Wed, Oct 7, 2020 at 10:33 PM John Hubbard <jhubbard@xxxxxxxxxx> wrote:
> > On 10/7/20 9:44 AM, Daniel Vetter wrote:
...
> > > @@ -398,15 +399,11 @@ static void g2d_userptr_put_dma_addr(struct g2d_data *g2d,
> > >        dma_unmap_sgtable(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt,
> > >                          DMA_BIDIRECTIONAL, 0);
> > >
> > > -     pages = frame_vector_pages(g2d_userptr->vec);
> > > -     if (!IS_ERR(pages)) {
> > > -             int i;
> > > +     for (i = 0; i < g2d_userptr->npages; i++)
> > > +             set_page_dirty_lock(g2d_userptr->pages[i]);
> > >
> > > -             for (i = 0; i < frame_vector_count(g2d_userptr->vec); i++)
> > > -                     set_page_dirty_lock(pages[i]);
> > > -     }
> > > -     put_vaddr_frames(g2d_userptr->vec);
> > > -     frame_vector_destroy(g2d_userptr->vec);
> > > +     unpin_user_pages(g2d_userptr->pages, g2d_userptr->npages);
> > > +     kvfree(g2d_userptr->pages);
> >
> > You can avoid writing your own loop, and just simplify the whole thing down to
> > two lines:
> >
> >          unpin_user_pages_dirty_lock(g2d_userptr->pages, g2d_userptr->npages,
> >                                      true);
> >          kvfree(g2d_userptr->pages);
>
> Oh nice, this is neat. I'll also roll it out in the habanalabs patch,
> that has the same thing. Well almost, it only uses set_page_dirty, not
> the _lock variant. But I have no idea whether that matters or not?


It matters. And invariably, call sites that use set_page_dirty() instead
of set_page_dirty_lock() were already wrong.  Which is why I never had to
provide anything like "unpin_user_pages_dirty (not locked)".

Although in habanalabs case, I just reviewed patch 3 and I think they *were*
correctly using set_page_dirty_lock()...

thanks,
--
John Hubbard
NVIDIA