Re: [PATCH 2/2 v4] drm/exynos: added userptr feature.

[KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx>]

(5/14/12 2:52 AM), Inki Dae wrote:
> > -----Original Message-----
> > From: KOSAKI Motohiro [mailto:kosaki.motohiro@xxxxxxxxx]
> > Sent: Monday, May 14, 2012 3:33 PM
> > To: Inki Dae
> > Cc: airlied@xxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; j.glisse@xxxxxxxxx;
> > minchan@xxxxxxxxxx; kyungmin.park@xxxxxxxxxxx; sw0312.kim@xxxxxxxxxxx;
> > jy0922.shim@xxxxxxxxxxx
> > Subject: Re: [PATCH 2/2 v4] drm/exynos: added userptr feature.
> >
> > > +       npages = buf->size>>  PAGE_SHIFT;
> >
> > Why round down? usually we use round up.
>
> The size was already rounded up by exynos_drm_gem_userptr_ioctl so this is
> just used to get page count.

got it.



> > > +       down_read(&current->mm->mmap_sem);
> > > +
> > > +       /*
> > > +        * Basically, all the pages from get_user_pages() can not be not
> > only
> > > +        * migrated by CMA but also swapped out.
> > > +        *
> > > +        * The migration issue.
> > > +        * - Pages reserved by CMA for some device using DMA could be
> > used by
> > > +        * kernel and if the device driver wants to use those pages
> > > +        * while being used by kernel then the pages are copied into
> > > +        * other ones allocated to migrate them and then finally,
> > > +        * the device driver can use the pages for itself.
> > > +        * Thus, migrated, the pages being accessed by DMA could be
> > changed
> > > +        * to other so this situation may incur that DMA accesses any
> > pages
> > > +        * it doesn't want.
> > > +        *
> > > +        * But the use of get_user_pages is safe from such magration
> > issue
> > > +        * because all the pages from get_user_pages CAN NOT be not only
> > > +        * migrated, but also swapped out.
> > > +        */
> > > +       get_npages = get_user_pages(current, current->mm, userptr,
> > > +                                       npages, write, 1, buf->pages,
> NULL);
> > Why force=1? It is almostly core-dump specific option. Why don't you
> > return
>
> I know that force indicates whether to force write access even  if user
> mapping is readonly.

right. and then, usually we don't want to ignore access permission. but note,
I'm only talk about generic thing. I have no knowledge drm area.



> so we just want to use pages from get_user_pages as
> read/write permission.

> > EFAULT when the page has write permission. IOW, Why your Xorg module
> > don't map memory w/ PROT_WRITE?
>
> No, Xorg can map memory w/ PROT_WRITE. Couldn't the Xorg map w/ PROT_WRITE
> if force = 1? plz, let me know if there is my missing point.

I meant, if Xorg always use PROT_WRITE, you don't need force=1.



_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/dri-devel