On Mon, Aug 12, 2024 at 12:41:39PM +0200, Thomas Zimmermann wrote: > Hi > > Am 12.08.24 um 12:18 schrieb Daniel Vetter: > > On Mon, Aug 12, 2024 at 11:23:44AM +0200, Daniel Vetter wrote: > > > On Mon, Aug 12, 2024 at 10:28:22AM +0200, Thomas Zimmermann wrote: > > > > Amdgpu and nouveau call vga_switcheroo_process_delayed_switch() from > > > > their lastclose callbacks. Call it from drm_lastclose(), so that the > > > > driver functions can finally be removed. Only PCI devices with enabled > > > > switcheroo do the delayed switching. The call has no effect on other > > > > hardware. > > > > > > > > v2: > > > > - move change to drm_lastclose() (Sima) > > > > - update docs for vga_switcheroo_process_delayed_switch() > > > > > > > > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx> > > > A bit an aside: The entire vgaswitcheroo code is still a midlayer mess, > > > where the locking is at the wrong layers resulting in the can_switch check > > > potentially being racy. But that's a different can of worms. > > Ok I got a bit annoyed about this mess again, and I think I have a > > reasonable idea for how to address it. Not sure why this took a decade, > > and definitely only pick this up if you're really bored. > > No, definitely not. :) I don't think I have hardware for testing > vga_switcheroo. Does this still exist? It seemed to be a thing of the 2000s. Yeah good chances the old style switcheroo doesn't have many, if any users left ... -Sima > > Best regards > Thomas > > > > > - We add a new vga_switcheroo_client_tryget, which checks the current > > state, and if it's on, increments a newly added refcount (which vgw > > switheroo maintains). Otherwise it fails. Drivers call this from their > > drm_driver->open hook. This check also allows us to drop the > > layer-violating checks in drm_open_helper for drm_dev->dev_power_state. > > > > - That refcount is dropped with vga_switcheroo_client_put, called from > > drm_driver->close. If the refcount drops to 0 this function also does > > delayed switch processing. > > > > - All the can_switch callbacks get removed and instead the vgwswr code > > directly consults its own refount. > > > > With this we don't have locking inversions anymore, and the old vgw > > switcheroo code works a lot more like the new mode based on runtime pm and > > power domains. > > > > With a bit more shuffling I think we can also ditch > > drm_driver->dev_power_state: > > > > - There's one in the intel backlight code, which is annoying, since it's > > wants to know whether the current callchain is from a vga switcheroo > > state change. But doable with a little helper. > > > > - Most others just want a vga_switcheroo_client_is_off() helper, which > > should be easy. Some are even entirely redundant, at least from a cursor > > callchain check. There's no races for these because they only matter > > during system suspend, since you should not mix both runtime and classic > > vgaswitcheroo logic. We might want some checks for that in that new > > helper ... > > > > - The one in the fbdev code is annoying, because it's another race. > > Ideally instead of that check it needs a call to > > vga_switcheroo_client_tryget/put just around the call to restore modes > > (we do not want fbdev to block state switches), but that probably means > > wiring a new callback through drm_client to drivers. > > > > - Might have missed a special case ... > > > > Anyway, I got nerdsniped, had an idea, figured best to type it up. Maybe > > we want to add a link to this to todo.rst, I think we have a vgaswitcheroo > > entry already. > > > > Cheers, Sima > > > > > > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > > > > > > > --- > > > > drivers/gpu/drm/drm_file.c | 4 ++++ > > > > drivers/gpu/vga/vga_switcheroo.c | 3 +-- > > > > 2 files changed, 5 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c > > > > index 714e42b05108..513bef816ae9 100644 > > > > --- a/drivers/gpu/drm/drm_file.c > > > > +++ b/drivers/gpu/drm/drm_file.c > > > > @@ -38,6 +38,7 @@ > > > > #include <linux/pci.h> > > > > #include <linux/poll.h> > > > > #include <linux/slab.h> > > > > +#include <linux/vga_switcheroo.h> > > > > #include <drm/drm_client.h> > > > > #include <drm/drm_drv.h> > > > > @@ -404,6 +405,9 @@ void drm_lastclose(struct drm_device * dev) > > > > drm_dbg_core(dev, "driver lastclose completed\n"); > > > > drm_client_dev_restore(dev); > > > > + > > > > + if (dev_is_pci(dev->dev)) > > > > + vga_switcheroo_process_delayed_switch(); > > > > } > > > > /** > > > > diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c > > > > index 365e6ddbe90f..18f2c92beff8 100644 > > > > --- a/drivers/gpu/vga/vga_switcheroo.c > > > > +++ b/drivers/gpu/vga/vga_switcheroo.c > > > > @@ -926,8 +926,7 @@ static void vga_switcheroo_debugfs_init(struct vgasr_priv *priv) > > > > /** > > > > * vga_switcheroo_process_delayed_switch() - helper for delayed switching > > > > * > > > > - * Process a delayed switch if one is pending. DRM drivers should call this > > > > - * from their ->lastclose callback. > > > > + * Process a delayed switch if one is pending. > > > > * > > > > * Return: 0 on success. -EINVAL if no delayed switch is pending, if the client > > > > * has unregistered in the meantime or if there are other clients blocking the > > > > -- > > > > 2.46.0 > > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > -- > -- > Thomas Zimmermann > Graphics Driver Developer > SUSE Software Solutions Germany GmbH > Frankenstrasse 146, 90461 Nuernberg, Germany > GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman > HRB 36809 (AG Nuernberg) > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
