[PATCH 3/3] drm/msm: hijack firmware fb's memory

[Rob Clark]

On Tue, Jul 11, 2017 at 10:42 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Tue, Jul 11, 2017 at 4:31 PM, Rob Clark <robdclark at gmail.com> wrote:
>> On Tue, Jul 11, 2017 at 10:03 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
>>> On Tue, Jul 11, 2017 at 3:38 PM, Rob Clark <robdclark at gmail.com> wrote:
>>>> +static unsigned long hijack_firmware_fb(struct drm_device *dev)
>>>> +{
>>>> +       struct msm_drm_private *priv = dev->dev_private;
>>>> +       unsigned long size;
>>>> +       int i;
>>>> +
>>>> +       /* if we have simplefb/efifb, find it's aperture and hijack
>>>> +        * that before we kick out the firmware fb's.
>>>> +        *
>>>> +        * TODO we probably should hold registration_lock
>>>> +        */
>>>> +       for (i = 0; i < FB_MAX; i++) {
>>>> +               struct fb_info *fb = get_fb_info(i);
>>>> +
>>>> +               if (IS_ERR_OR_NULL(fb))
>>>> +                       continue;
>>>> +
>>>> +               if (!fb->apertures->count)
>>>> +                       continue;
>>>> +
>>>> +               /* if we find efifb or simplefb, we are about to
>>>> +                * kick them out, so hijack their memory:
>>>> +                */
>>>> +               if ((strcmp(fb->fix.id, "EFI VGA") == 0) ||
>>>> +                               (strcmp(fb->fix.id, "simple") == 0)) {
>>>> +
>>>> +                       priv->vram.paddr = fb->apertures->ranges[0].base;
>>>> +                       size = fb->apertures->ranges[0].size;
>>>> +               }
>>>> +
>>>> +               put_fb_info(fb);
>>>> +
>>>> +               if (size)
>>>> +                       return size;
>>>> +       }
>>>> +
>>>> +       return 0;
>>>> +}
>>>
>>> I think this should be a helper function in at least drm_fb_helper.c,
>>> which would then fill in both base&size in a passed-in struct. But
>>> yeah this seems a lot better than the old one.
>>
>> Yeah, I guess we could do that.. but probably not in drm_fb_helper.c
>> since that is compile-time optional.  Better suggestions about where
>> it should live?  If you have fbdev but not DRM_FBDEV_EMULATION you
>> still want to do this, I think.  Otherwise we can't completely take
>> over the display setup by firmware (ie. no way to create
>> plane->state->fb).
>
> Hm right, maybe add a drm_fwfb_helper.c or so. If you look at
> i915_kick_out_vgacon(), that might be another candidate for that file.
> Putting it into fbdev itself seems like a bad idea, because
> maintenance pains.

Hmm, would it be weird to have an:

  obj-$(CONFIG_FB) += drm_fbfw_helper.o

in drm/Makefile?  Or is there a better way to do that?

I'm also wondering a bit about the CONFIG_FB=n case.. you might still
have CONFIG_EFI, so maybe we should fall back to pulling this out of
screen_info and looking for a simple-framebuffer node in the CONFIG_OF
case?

(also maybe worth noting that on ARM/ARM64 we don't have
CONFIG_VGA_CONSOLE.. so there are a lot of fun permutations..)

BR,
-R