[PATCH] char/agp: Disable frontend without CONFIG_DRM_LEGACY

[Thomas Zimmermann]

Hi

Am 18.11.20 um 09:53 schrieb Daniel Vetter:
> On Wed, Nov 18, 2020 at 9:24 AM Christian König
> <christian.koenig at amd.com> wrote:
>>
>> Am 18.11.20 um 09:02 schrieb Thomas Zimmermann:
>>> Hi
>>>
>>> Am 17.11.20 um 22:40 schrieb Daniel Vetter:
>>>> It's probably full of bugs ready for exploiting by userspace. And
>>>> there's not going to be any userspace for this without any of the drm
>>>> legacy drivers enabled too. So just couple it together.
>>>>
>>>> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
>>>> Cc: David Airlie <airlied at linux.ie>
>>>> Cc: Adam Jackson <ajax at redhat.com>
>>>> ---
>>>>    drivers/char/agp/Makefile | 6 +++++-
>>>>    drivers/char/agp/agp.h    | 5 +++++
>>>>    2 files changed, 10 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/char/agp/Makefile b/drivers/char/agp/Makefile
>>>> index cb2497d157f6..90ed8c789e48 100644
>>>> --- a/drivers/char/agp/Makefile
>>>> +++ b/drivers/char/agp/Makefile
>>>> @@ -1,7 +1,11 @@
>>>>    # SPDX-License-Identifier: GPL-2.0
>>>> -agpgart-y := backend.o frontend.o generic.o isoch.o
>>>> +agpgart-y := backend.o generic.o isoch.o
>>>>
>>>> +ifeq ($(CONFIG_DRM_LEGACY),y)
>>>>    agpgart-$(CONFIG_COMPAT)   += compat_ioctl.o
>>>> +agpgart-y                   += frontend.o
>>>> +endif
>>>> +
>>>>
>>>>    obj-$(CONFIG_AGP)          += agpgart.o
>>>>    obj-$(CONFIG_AGP_ALI)              += ali-agp.o
>>>> diff --git a/drivers/char/agp/agp.h b/drivers/char/agp/agp.h
>>>> index 4eb1c772ded7..bb09d64cd51e 100644
>>>> --- a/drivers/char/agp/agp.h
>>>> +++ b/drivers/char/agp/agp.h
>>>> @@ -186,8 +186,13 @@ int agp_add_bridge(struct agp_bridge_data *bridge);
>>>>    void agp_remove_bridge(struct agp_bridge_data *bridge);
>>>>
>>>>    /* Frontend routines. */
>>>> +#if IS_ENABLED(CONFIG_DRM_LEGACY)
>>>>    int agp_frontend_initialize(void);
>>>>    void agp_frontend_cleanup(void);
>>>> +#else
>>>> +static inline int agp_frontend_initialize(void) { return 0; }
>>>> +static inline void agp_frontend_cleanup(void) {}
>>>> +#endif
>>> There's one non-legacy driver that uses these agp structures, which is
>>> radeon. Does this change affect radeon?
>>
>> Nouveau uses AGP as well, but I'm not sure if both drivers use any of
>> this stuff.
> 
> frontend = /dev/agp chardev interface for userspace drivers. If you're
> looking at kernel drivers, you're looking at the wrong thing, the
> kernel-internal interface is in char/agp/backend.c and still enabled.
> So no impact at all on any kernel code.
> 
> Now the impact this does have on kms drivers using agp is that there's
> no longer a userspace ioctl interface to change the agp setup and
> mappings and fight the kms driver (which assumes it's fully in control
> of agp configuration).

Thanks for clarifying. I'm certainly not qualified, but still

Acked-by: Thomas Zimmermann <tzimmermann at suse.de>

Best regards
Thomas

> -Daniel
> 
>>
>> Regards,
>> Christian.
>>
>>>
>>> Best regards
>>> Thomas
>>>
>>>>
>>>>    /* Generic routines. */
>>>>    void agp_generic_enable(struct agp_bridge_data *bridge, u32 mode);
>>>>
>>
> 
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer
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