[PATCH] drm/vmwgfx: Re-introduce drm_crtc_helper_funcs::prepare

[Daniel Vetter]

On Fri, May 03, 2024 at 10:46:40PM -0400, Zack Rusin wrote:
> On Fri, May 3, 2024 at 6:29 PM Ian Forbes <ian.forbes at broadcom.com> wrote:
> >
> > This function was removed in the referenced fixes commit and caused a
> > regression. This is because the presence of this function, even though it
> > is a noop, changes the behaviour of disable_outputs in
> > drm_atomic_helper.c:1211.
> >
> > Fixes: 7b0062036c3b ("drm/vmwgfx: Implement virtual crc generation")
> > Signed-off-by: Ian Forbes <ian.forbes at broadcom.com>
> > ---
> >  drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c b/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
> > index 2041c4d48daa..37223f95cbec 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
> > @@ -409,6 +409,10 @@ static void vmw_stdu_crtc_mode_set_nofb(struct drm_crtc *crtc)
> >                           crtc->x, crtc->y);
> >  }
> >
> > +static void vmw_stdu_crtc_helper_prepare(struct drm_crtc *crtc)
> > +{
> > +}
> > +
> >  static void vmw_stdu_crtc_atomic_disable(struct drm_crtc *crtc,
> >                                          struct drm_atomic_state *state)
> >  {
> > @@ -1463,6 +1467,7 @@ drm_plane_helper_funcs vmw_stdu_primary_plane_helper_funcs = {
> >  };
> >
> >  static const struct drm_crtc_helper_funcs vmw_stdu_crtc_helper_funcs = {
> > +       .prepare = vmw_stdu_crtc_helper_prepare,
> >         .mode_set_nofb = vmw_stdu_crtc_mode_set_nofb,
> >         .atomic_check = vmw_du_crtc_atomic_check,
> >         .atomic_begin = vmw_du_crtc_atomic_begin,
> > --
> > 2.34.1
> >
> 
> Thanks, but that doesn't look correct. We do want to make sure the
> drm_crtc_vblank_off is actually called when outputs are disabled.
> Since this is my regression it's perfectly fine if you want to hand it
> off to me and work on something else. In general you always want to
> understand what the patch that you're sending is doing before sending
> it. In this case it's pretty trivial, the commit you mention says that
> it fixes kms_pipe_crc_basic and if you run it with your patch (e.g.
> sudo ./kms_pipe_crc_basic --run-subtest disable-crc-after-crtc) you
> should notice:

Rather aside, but atomic helpers supporting the ->prepare callback in that
special way is kinda a remnant of the conversion helpers to move legacy
kms drivers to atomic.

Which means we might want to look into whether anyone still needs that, or
whether the ->atomic_disable hook is enough and then nuke that if-ladder
of compat code. Because as this bug shows, it's rather surprising special
case :-/
-Sima

> May 03 22:25:05 fedora.local kernel: ------------[ cut here ]------------
> May 03 22:25:05 fedora.local kernel: driver forgot to call drm_crtc_vblank_off()
> May 03 22:25:05 fedora.local kernel: WARNING: CPU: 2 PID: 2204 at
> drivers/gpu/drm/drm_atomic_helper.c:1232 disable_outputs+0x345/0x350
> May 03 22:25:05 fedora.local kernel: Modules linked in: snd_seq_dummy
> snd_hrtimer nf_conntrack_netbios_ns nf_conntrack_broadcast
> nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet
> nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat
> nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables
> snd_seq_midi snd_seq_midi_event qrtr vsock_loopback
> vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock
> sunrpc binfmt_misc snd_ens1371 snd_ac97_codec ac97_bus snd_seq
> intel_rapl_msr snd_pcm intel_rapl_common vmw_balloon
> intel_uncore_frequency_common isst_if_mbox_msr isst_if_common gameport
> snd_rawmidi snd_seq_device rapl snd_timer snd vmw_vmci pcspkr
> soundcore i2c_piix4 pktcdvd joydev loop nfnetlink zram vmwgfx
> crct10dif_pclmul crc32_pclmul crc32c_intel polyval_clmulni
> polyval_generic nvme ghash_clmulni_intel nvme_core sha512_ssse3
> sha256_ssse3 sha1_ssse3 drm_ttm_helper ttm nvme_auth vmxnet3 serio_raw
> ata_generic pata_acpi fuse i2c_dev
> May 03 22:25:05 fedora.local kernel: CPU: 2 PID: 2204 Comm:
> kms_pipe_crc_ba Not tainted 6.9.0-rc2-vmwgfx #5
> May 03 22:25:05 fedora.local kernel: Hardware name: VMware, Inc.
> VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00
> 11/12/2020
> May 03 22:25:05 fedora.local kernel: RIP: 0010:disable_outputs+0x345/0x350
> ... but in most cases it's not going to be so trivial. Whether you
> decide to work on this one yourself or hand it off to me - we don't
> want to trade bug for bug here, but fix both of those things.
> 
> z

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch