[PATCH 01/43] drm/fbdev-generic: Do not set physical framebuffer address

[Maxime Ripard]

On Mon, Mar 18, 2024 at 08:59:01AM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 18.03.24 um 03:35 schrieb Zack Rusin:
> > On Tue, Mar 12, 2024 at 11:48 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
> > > Framebuffer memory is allocated via vmalloc() from non-contiguous
> > > physical pages. The physical framebuffer start address is therefore
> > > meaningless. Do not set it.
> > > 
> > > The value is not used within the kernel and only exported to userspace
> > > on dedicated ARM configs. No functional change is expected.
> > > 
> > > Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> > > Fixes: a5b44c4adb16 ("drm/fbdev-generic: Always use shadow buffering")
> > > Cc: Thomas Zimmermann <tzimmermann at suse.de>
> > > Cc: Javier Martinez Canillas <javierm at redhat.com>
> > > Cc: Zack Rusin <zackr at vmware.com>
> > > Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > > Cc: Maxime Ripard <mripard at kernel.org>
> > > Cc: <stable at vger.kernel.org> # v6.4+
> > > ---
> > >   drivers/gpu/drm/drm_fbdev_generic.c | 1 -
> > >   1 file changed, 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_fbdev_generic.c b/drivers/gpu/drm/drm_fbdev_generic.c
> > > index d647d89764cb9..b4659cd6285ab 100644
> > > --- a/drivers/gpu/drm/drm_fbdev_generic.c
> > > +++ b/drivers/gpu/drm/drm_fbdev_generic.c
> > > @@ -113,7 +113,6 @@ static int drm_fbdev_generic_helper_fb_probe(struct drm_fb_helper *fb_helper,
> > >          /* screen */
> > >          info->flags |= FBINFO_VIRTFB | FBINFO_READS_FAST;
> > >          info->screen_buffer = screen_buffer;
> > > -       info->fix.smem_start = page_to_phys(vmalloc_to_page(info->screen_buffer));
> > >          info->fix.smem_len = screen_size;
> > > 
> > >          /* deferred I/O */
> > > --
> > > 2.44.0
> > > 
> > Good idea. I think given that drm_leak_fbdev_smem is off by default we
> > could remove the setting of smem_start by all of the in-tree drm
> > drivers (they all have open source userspace that won't mess around
> > with fbdev fb) - it will be reset to 0 anyway. Actually, I wonder if
> > we still need drm_leak_fbdev_smem at all...
> 
> All I know is that there's an embedded userspace driver that requires that
> setting. I don't even know which hardware.

The original Mali driver (ie, lima) used to require it, that's why we
introduced it in the past.

I'm not sure if the newer versions of that driver, or if newer Mali
generations (ie, panfrost and panthor) closed source driver would
require it, so it might be worth removing if it's easy enough to revert.

Maxime
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