Re: [PATCH] drm/ttm: provide default page protection for UML

[David Gow]

On Thu, Sep 2, 2021 at 10:46 PM Daniel Vetter <daniel@xxxxxxxx> wrote:
>
> On Thu, Sep 02, 2021 at 07:19:01AM +0100, Anton Ivanov wrote:
> > On 02/09/2021 06:52, Randy Dunlap wrote:
> > > On 9/1/21 10:48 PM, Anton Ivanov wrote:
> > > > On 02/09/2021 03:01, Randy Dunlap wrote:
> > > > > boot_cpu_data [struct cpuinfo_um (on UML)] does not have a struct
> > > > > member named 'x86', so provide a default page protection mode
> > > > > for CONFIG_UML.
> > > > >
> > > > > Mends this build error:
> > > > > ../drivers/gpu/drm/ttm/ttm_module.c: In function
> > > > > ‘ttm_prot_from_caching’:
> > > > > ../drivers/gpu/drm/ttm/ttm_module.c:59:24: error: ‘struct
> > > > > cpuinfo_um’ has no member named ‘x86’
> > > > >    else if (boot_cpu_data.x86 > 3)
> > > > >                          ^
> > > > >
> > > > > Fixes: 3bf3710e3718 ("drm/ttm: Add a generic TTM memcpy move for
> > > > > page-based iomem")
> > > > > Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> > > > > Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> > > > > Cc: Christian König <christian.koenig@xxxxxxx>
> > > > > Cc: Huang Rui <ray.huang@xxxxxxx>
> > > > > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > > > > Cc: Jeff Dike <jdike@xxxxxxxxxxx>
> > > > > Cc: Richard Weinberger <richard@xxxxxx>
> > > > > Cc: Anton Ivanov <anton.ivanov@xxxxxxxxxxxxxxxxxx>
> > > > > Cc: linux-um@xxxxxxxxxxxxxxxxxxx
> > > > > Cc: David Airlie <airlied@xxxxxxxx>
> > > > > Cc: Daniel Vetter <daniel@xxxxxxxx>
> > > > > ---
> > > > >   drivers/gpu/drm/ttm/ttm_module.c |    4 ++++
> > > > >   1 file changed, 4 insertions(+)
> > > > >
> > > > > --- linux-next-20210901.orig/drivers/gpu/drm/ttm/ttm_module.c
> > > > > +++ linux-next-20210901/drivers/gpu/drm/ttm/ttm_module.c
> > > > > @@ -53,6 +53,9 @@ pgprot_t ttm_prot_from_caching(enum ttm_
> > > > >       if (caching == ttm_cached)
> > > > >           return tmp;
> > > > > +#ifdef CONFIG_UML
> > > > > +    tmp = pgprot_noncached(tmp);
> > > > > +#else
> > > > >   #if defined(__i386__) || defined(__x86_64__)
> > > > >       if (caching == ttm_write_combined)
> > > > >           tmp = pgprot_writecombine(tmp);
> > > > > @@ -69,6 +72,7 @@ pgprot_t ttm_prot_from_caching(enum ttm_
> > > > >   #if defined(__sparc__)
> > > > >       tmp = pgprot_noncached(tmp);
> > > > >   #endif
> > > > > +#endif
> > > > >       return tmp;
> > > > >   }
> > > >
> > > > Patch looks OK.
> > > >
> > > > I have a question though - why all of DRM is not !UML in config. Not
> > > > like we can use them.
> > >
> > > I have no idea about that.
> > > Hopefully one of the (other) UML maintainers can answer you.
> >
> > Touche.
> >
> > We will discuss that and possibly push a patch to !UML that part of the
> > tree. IMHO it is not applicable.
>
> I thought kunit is based on top of uml, and we do want to eventually adopt
> that. Especially for helper libraries like ttm.

UML is not actually a dependency for KUnit, so it's definitely
possible to test things which aren't compatible with UML. (In fact,
there's even now some tooling support to use qemu instead on a number
of architectures.)

That being said, the KUnit tooling does use UML by default, so if it's
not too difficult to keep some level of UML support, it'll make it a
little easier (and faster) for people to run any KUnit tests.

Cheers,
-- David