[bug report] drm/panthor: Add the scheduler logical block

[Dan Carpenter]

On Wed, Apr 10, 2024 at 03:11:52PM +0100, Steven Price wrote:
> On 08/04/2024 08:35, Dan Carpenter wrote:
> > Hello Boris Brezillon,
> > 
> > Commit de8548813824 ("drm/panthor: Add the scheduler logical block")
> > from Feb 29, 2024 (linux-next), leads to the following Smatch static
> > checker warning:
> > 
> > 	drivers/gpu/drm/panthor/panthor_sched.c:1153 csg_slot_sync_state_locked()
> > 	error: uninitialized symbol 'new_state'.
> > 
> > drivers/gpu/drm/panthor/panthor_sched.c
> >     1123 static void
> >     1124 csg_slot_sync_state_locked(struct panthor_device *ptdev, u32 csg_id)
> >     1125 {
> >     1126         struct panthor_csg_slot *csg_slot = &ptdev->scheduler->csg_slots[csg_id];
> >     1127         struct panthor_fw_csg_iface *csg_iface;
> >     1128         struct panthor_group *group;
> >     1129         enum panthor_group_state new_state, old_state;
> >     1130 
> >     1131         lockdep_assert_held(&ptdev->scheduler->lock);
> >     1132 
> >     1133         csg_iface = panthor_fw_get_csg_iface(ptdev, csg_id);
> >     1134         group = csg_slot->group;
> >     1135 
> >     1136         if (!group)
> >     1137                 return;
> >     1138 
> >     1139         old_state = group->state;
> >     1140         switch (csg_iface->output->ack & CSG_STATE_MASK) {
> >                                                   ^^^^^^^^^^^^^^
> > This mask is 0x7.  Should it be 0x3?  That would silence the static
> > checker warning.
> 
> The mask is correct - it's effectively a hardware register (well it's
> read/written by the firmware on the hardware). States 4-7 are officially
> "reserved" and Should Not Happen™!
> 
> I guess a "default:" case with a WARN_ON() would be the right solution.
> 
> Steve

A WARN_ON() won't silence the warning.  Plus WARN_ON() is not free in
terms of memory usage.  And they're kind of controversial these days to
be honest.

One solution would be to just ignore the static checker warning.  These
are a one time thing, and if people have questions in the future, they
can just search lore for this thread.

regards,
dan carpenter