Message-ID: <CAAFQd5BW46w7e=H2qpOyoFXTbJJ=RsAoDWHcXXQVLPGQqgVomw@mail.gmail.com>
Date:   Tue, 27 Nov 2018 16:54:08 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Gustavo Padovan <gustavo.padovan@...labora.com>
Cc:     helen.koike@...labora.com, mzoran@...wfest.net,
        Eric Anholt <eric@...olt.net>,
        Sandy Huang <hjc@...k-chips.com>,
        Heiko Stübner <heiko@...ech.de>,
        David Airlie <airlied@...ux.ie>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <joro@...tes.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <linux-arm-kernel@...ts.infradead.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Sean Paul <seanpaul@...gle.com>, kernel@...labora.com,
        Stéphane Marchesin <marcheu@...gle.com>
Subject: Re: [PATCH v3] drm/rockchip: update cursors asynchronously through atomic.

Hi Gustavo,

On Tue, Nov 27, 2018 at 8:54 AM Gustavo Padovan
<gustavo.padovan@...labora.com> wrote:
>
> Hi Tomasz,
>
> On 11/23/18 12:27 AM, Tomasz Figa wrote:
> > Hi Helen,
> >
> > On Fri, Nov 23, 2018 at 8:31 AM Helen Koike <helen.koike@...labora.com> wrote:
> >> Hi Tomasz,
> >>
> >> On 11/20/18 4:48 AM, Tomasz Figa wrote:
> >>> Hi Helen,
> >>>
> >>> On Tue, Nov 20, 2018 at 4:08 AM Helen Koike <helen.koike@...labora.com> wrote:
> >>>> From: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> >>>>
> >>>> Add support to async updates of cursors by using the new atomic
> >>>> interface for that.
> >>>>
> >>>> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> >>>> [updated for upstream]
> >>>> Signed-off-by: Helen Koike <helen.koike@...labora.com>
> >>>>
> >>>> ---
> >>>> Hello,
> >>>>
> >>>> This is the third version of the async-plane update suport to the
> >>>> Rockchip driver.
> >>>>
> >>> Thanks for a quick respin. Please see my comments inline. (I'll try to
> >>> be better at responding from now on...)
> >>>
> >>>> I tested running igt kms_cursor_legacy and kms_atomic tests using a 96Boards Ficus.
> >>>>
> >>>> Note that before the patch, the following igt tests failed:
> >>>>
> >>>>          basic-flip-before-cursor-atomic
> >>>>          basic-flip-before-cursor-legacy
> >>>>          cursor-vs-flip-atomic
> >>>>          cursor-vs-flip-legacy
> >>>>          cursor-vs-flip-toggle
> >>>>          flip-vs-cursor-atomic
> >>>>          flip-vs-cursor-busy-crc-atomic
> >>>>          flip-vs-cursor-busy-crc-legacy
> >>>>          flip-vs-cursor-crc-atomic
> >>>>          flip-vs-cursor-crc-legacy
> >>>>          flip-vs-cursor-legacy
> >>>>
> >>>> Full log: https://people.collabora.com/~koike/results-4.20/html/
> >>>>
> >>>> Now with the patch applied the following were fixed:
> >>>>          basic-flip-before-cursor-atomic
> >>>>          basic-flip-before-cursor-legacy
> >>>>          flip-vs-cursor-atomic
> >>>>          flip-vs-cursor-legacy
> >>>>
> >>>> Full log: https://people.collabora.com/~koike/results-4.20-async/html/
> >>> Could you also test modetest, with the -C switch to test the legacy
> >>> cursor API? I remember it triggering crashes due to synchronization
> >>> issues easily.
> >> Sure. I tested with
> >> $ modetest -M rockchip -s 37:1920x1080 -C
> >>
> >> I also vary the mode but I couldn't trigger any crashes.
> >>
> >>>> Tomasz, as you mentined in v2 about waiting the hardware before updating
> >>>> the framebuffer, now I call the loop you pointed out in the async path,
> >>>> was that what you had in mind? Or do you think I would make sense to
> >>>> call the vop_crtc_atomic_flush() instead of just exposing that loop?
> >>>>
> >>>> Thanks
> >>>> Helen
> >>>>
> >>>> Changes in v3:
> >>>> - Rebased on top of drm-misc
> >>>> - Fix missing include in rockchip_drm_vop.c
> >>>> - New function vop_crtc_atomic_commit_flush
> >>>>
> >>>> Changes in v2:
> >>>> - v2: https://patchwork.freedesktop.org/patch/254180/
> >>>> - Change the framebuffer as well to cover jumpy cursor when hovering
> >>>>    text boxes or hyperlink. (Tomasz)
> >>>> - Use the PSR inhibit mechanism when accessing VOP hardware instead of
> >>>>    PSR flushing (Tomasz)
> >>>>
> >>>> Changes in v1:
> >>>> - Rebased on top of drm-misc
> >>>> - In async_check call drm_atomic_helper_check_plane_state to check that
> >>>>    the desired plane is valid and update various bits of derived state
> >>>>    (clipped coordinates etc.)
> >>>> - In async_check allow to configure new scaling in the fast path.
> >>>> - In async_update force to flush all registered PSR encoders.
> >>>> - In async_update call atomic_update directly.
> >>>> - In async_update call vop_cfg_done needed to set the vop registers and take effect.
> >>>>
> >>>>   drivers/gpu/drm/rockchip/rockchip_drm_fb.c  |  36 -------
> >>>>   drivers/gpu/drm/rockchip/rockchip_drm_psr.c |  37 +++++++
> >>>>   drivers/gpu/drm/rockchip/rockchip_drm_psr.h |   3 +
> >>>>   drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 108 +++++++++++++++++---
> >>>>   4 files changed, 131 insertions(+), 53 deletions(-)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> >>>> index ea18cb2a76c0..08bec50d9c5d 100644
> >>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> >>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> >>>> @@ -127,42 +127,6 @@ rockchip_user_fb_create(struct drm_device *dev, struct drm_file *file_priv,
> >>>>          return ERR_PTR(ret);
> >>>>   }
> >>>>
> >>>> -static void
> >>>> -rockchip_drm_psr_inhibit_get_state(struct drm_atomic_state *state)
> >>>> -{
> >>>> -       struct drm_crtc *crtc;
> >>>> -       struct drm_crtc_state *crtc_state;
> >>>> -       struct drm_encoder *encoder;
> >>>> -       u32 encoder_mask = 0;
> >>>> -       int i;
> >>>> -
> >>>> -       for_each_old_crtc_in_state(state, crtc, crtc_state, i) {
> >>>> -               encoder_mask |= crtc_state->encoder_mask;
> >>>> -               encoder_mask |= crtc->state->encoder_mask;
> >>>> -       }
> >>>> -
> >>>> -       drm_for_each_encoder_mask(encoder, state->dev, encoder_mask)
> >>>> -               rockchip_drm_psr_inhibit_get(encoder);
> >>>> -}
> >>>> -
> >>>> -static void
> >>>> -rockchip_drm_psr_inhibit_put_state(struct drm_atomic_state *state)
> >>>> -{
> >>>> -       struct drm_crtc *crtc;
> >>>> -       struct drm_crtc_state *crtc_state;
> >>>> -       struct drm_encoder *encoder;
> >>>> -       u32 encoder_mask = 0;
> >>>> -       int i;
> >>>> -
> >>>> -       for_each_old_crtc_in_state(state, crtc, crtc_state, i) {
> >>>> -               encoder_mask |= crtc_state->encoder_mask;
> >>>> -               encoder_mask |= crtc->state->encoder_mask;
> >>>> -       }
> >>>> -
> >>>> -       drm_for_each_encoder_mask(encoder, state->dev, encoder_mask)
> >>>> -               rockchip_drm_psr_inhibit_put(encoder);
> >>>> -}
> >>>> -
> >>>>   static void
> >>>>   rockchip_atomic_helper_commit_tail_rpm(struct drm_atomic_state *old_state)
> >>>>   {
> >>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_psr.c b/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
> >>>> index 01ff3c858875..22a70ab6e214 100644
> >>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
> >>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
> >>>> @@ -13,6 +13,7 @@
> >>>>    */
> >>>>
> >>>>   #include <drm/drmP.h>
> >>>> +#include <drm/drm_atomic.h>
> >>>>   #include <drm/drm_crtc_helper.h>
> >>>>
> >>>>   #include "rockchip_drm_drv.h"
> >>>> @@ -109,6 +110,42 @@ int rockchip_drm_psr_inhibit_put(struct drm_encoder *encoder)
> >>>>   }
> >>>>   EXPORT_SYMBOL(rockchip_drm_psr_inhibit_put);
> >>>>
> >>>> +void rockchip_drm_psr_inhibit_get_state(struct drm_atomic_state *state)
> >>>> +{
> >>>> +       struct drm_crtc *crtc;
> >>>> +       struct drm_crtc_state *crtc_state;
> >>>> +       struct drm_encoder *encoder;
> >>>> +       u32 encoder_mask = 0;
> >>>> +       int i;
> >>>> +
> >>>> +       for_each_old_crtc_in_state(state, crtc, crtc_state, i) {
> >>>> +               encoder_mask |= crtc_state->encoder_mask;
> >>>> +               encoder_mask |= crtc->state->encoder_mask;
> >>>> +       }
> >>>> +
> >>>> +       drm_for_each_encoder_mask(encoder, state->dev, encoder_mask)
> >>>> +               rockchip_drm_psr_inhibit_get(encoder);
> >>>> +}
> >>>> +EXPORT_SYMBOL(rockchip_drm_psr_inhibit_get_state);
> >>>> +
> >>>> +void rockchip_drm_psr_inhibit_put_state(struct drm_atomic_state *state)
> >>>> +{
> >>>> +       struct drm_crtc *crtc;
> >>>> +       struct drm_crtc_state *crtc_state;
> >>>> +       struct drm_encoder *encoder;
> >>>> +       u32 encoder_mask = 0;
> >>>> +       int i;
> >>>> +
> >>>> +       for_each_old_crtc_in_state(state, crtc, crtc_state, i) {
> >>>> +               encoder_mask |= crtc_state->encoder_mask;
> >>>> +               encoder_mask |= crtc->state->encoder_mask;
> >>>> +       }
> >>>> +
> >>>> +       drm_for_each_encoder_mask(encoder, state->dev, encoder_mask)
> >>>> +               rockchip_drm_psr_inhibit_put(encoder);
> >>>> +}
> >>>> +EXPORT_SYMBOL(rockchip_drm_psr_inhibit_put_state);
> >>>> +
> >>>>   /**
> >>>>    * rockchip_drm_psr_inhibit_get - acquire PSR inhibit on given encoder
> >>>>    * @encoder: encoder to obtain the PSR encoder
> >>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_psr.h b/drivers/gpu/drm/rockchip/rockchip_drm_psr.h
> >>>> index 860c62494496..25350ba3237b 100644
> >>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_psr.h
> >>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_psr.h
> >>>> @@ -20,6 +20,9 @@ void rockchip_drm_psr_flush_all(struct drm_device *dev);
> >>>>   int rockchip_drm_psr_inhibit_put(struct drm_encoder *encoder);
> >>>>   int rockchip_drm_psr_inhibit_get(struct drm_encoder *encoder);
> >>>>
> >>>> +void rockchip_drm_psr_inhibit_get_state(struct drm_atomic_state *state);
> >>>> +void rockchip_drm_psr_inhibit_put_state(struct drm_atomic_state *state);
> >>>> +
> >>>>   int rockchip_drm_psr_register(struct drm_encoder *encoder,
> >>>>                          int (*psr_set)(struct drm_encoder *, bool enable));
> >>>>   void rockchip_drm_psr_unregister(struct drm_encoder *encoder);
> >>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> >>>> index fb70fb486fbf..176d6e8207ed 100644
> >>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> >>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> >>>> @@ -15,6 +15,7 @@
> >>>>   #include <drm/drm.h>
> >>>>   #include <drm/drmP.h>
> >>>>   #include <drm/drm_atomic.h>
> >>>> +#include <drm/drm_atomic_uapi.h>
> >>>>   #include <drm/drm_crtc.h>
> >>>>   #include <drm/drm_crtc_helper.h>
> >>>>   #include <drm/drm_flip_work.h>
> >>>> @@ -819,10 +820,99 @@ static void vop_plane_atomic_update(struct drm_plane *plane,
> >>>>          spin_unlock(&vop->reg_lock);
> >>>>   }
> >>>>
> >>>> +static int vop_plane_atomic_async_check(struct drm_plane *plane,
> >>>> +                                       struct drm_plane_state *state)
> >>>> +{
> >>>> +       struct vop_win *vop_win = to_vop_win(plane);
> >>>> +       const struct vop_win_data *win = vop_win->data;
> >>>> +       int min_scale = win->phy->scl ? FRAC_16_16(1, 8) :
> >>>> +                                       DRM_PLANE_HELPER_NO_SCALING;
> >>>> +       int max_scale = win->phy->scl ? FRAC_16_16(8, 1) :
> >>>> +                                       DRM_PLANE_HELPER_NO_SCALING;
> >>>> +       struct drm_crtc_state *crtc_state;
> >>>> +       int ret;
> >>>> +
> >>>> +       if (plane != state->crtc->cursor)
> >>>> +               return -EINVAL;
> >>>> +
> >>>> +       if (!plane->state)
> >>>> +               return -EINVAL;
> >>>> +
> >>>> +       if (!plane->state->fb)
> >>>> +               return -EINVAL;
> >>>> +
> >>>> +       if (state->state)
> >>>> +               crtc_state = drm_atomic_get_existing_crtc_state(state->state,
> >>>> +                                                               state->crtc);
> >>>> +       else /* Special case for asynchronous cursor updates. */
> >>>> +               crtc_state = plane->crtc->state;
> >>>> +
> >>>> +       ret = drm_atomic_helper_check_plane_state(plane->state,
> >>>> +                                                 crtc_state,
> >>>> +                                                 min_scale, max_scale,
> >>>> +                                                 true, true);
> >>>> +       return ret;
> >>>> +}
> >>>> +
> >>>> +static void vop_crtc_atomic_commit_flush(struct drm_crtc *crtc,
> >>>> +                                        struct drm_crtc_state *old_crtc_state)
> >>>> +{
> >>>> +       struct drm_atomic_state *old_state = old_crtc_state->state;
> >>>> +       struct drm_plane_state *old_plane_state, *new_plane_state;
> >>>> +       struct vop *vop = to_vop(crtc);
> >>>> +       struct drm_plane *plane;
> >>>> +       int i;
> >>>> +
> >>>> +       for_each_oldnew_plane_in_state(old_state, plane, old_plane_state,
> >>>> +                                      new_plane_state, i) {
> >>> Hmm, from what I can see, we're not going through the full atomic
> >>> commit sequence, with state flip, so I'm not sure where we would get
> >>> the new state here from.
> >>>
> >>>> +               if (!old_plane_state->fb)
> >>>> +                       continue;
> >>>> +
> >>>> +               if (old_plane_state->fb == new_plane_state->fb)
> >>>> +                       continue;
> >>>> +
> >>>> +               drm_framebuffer_get(old_plane_state->fb);
> >>>> +               WARN_ON(drm_crtc_vblank_get(crtc) != 0);
> >>>> +               drm_flip_work_queue(&vop->fb_unref_work, old_plane_state->fb);
> >>>> +               set_bit(VOP_PENDING_FB_UNREF, &vop->pending);
> >>>> +       }
> >>>> +}
> >>>> +
> >>>> +static void vop_plane_atomic_async_update(struct drm_plane *plane,
> >>>> +                                         struct drm_plane_state *new_state)
> >>>> +{
> >>>> +       struct vop *vop = to_vop(plane->state->crtc);
> >>>> +
> >>>> +       if (vop->crtc.state->state)
> >>>> +               vop_crtc_atomic_commit_flush(&vop->crtc, vop->crtc.state);
> >>> Since we just operate on one plane here, we could just do like this:
> >>>
> >>> if (plane->state->fb && plane->state->fb != new_state->fb) {
> >>>                 drm_framebuffer_get(plane->state->fb);
> >>>                 WARN_ON(drm_crtc_vblank_get(crtc) != 0);
> >>>                 drm_flip_work_queue(&vop->fb_unref_work, plane->state->fb);
> >>>                 set_bit(VOP_PENDING_FB_UNREF, &vop->pending);
> >>> }
> >>>
> >>> However, we cannot simply to this here, because it races with the
> >>> vblank interrupt. We need to program the hw plane with the new fb
> >>> first and trigger the update. This needs all the careful handling that
> >>> is done in vop_crtc_atomic_flush() and so my original suggestion to
> >>> just call it.
> >> vop_crtc_atomic_flush() also updates the crtc->state->event, I don't
> >> think we want that.
> > Good point, we don't want to touch the event.
> >
> >> And actually I don't think we have this race condition, please see below
> >>
> > Just to clarify, the race conditions I'm talking here are not anything
> > new to this patch alone. I had actually observed those when
> > implementing the Chrome OS downstream async cursor code before:
> >
> > https://chromium.googlesource.com/chromiumos/third_party/kernel/+/65d4ff0af3f8c7ebecad8f3b402b546f277d9225/drivers/gpu/drm/rockchip/rockchip_drm_vop.c#1015
> >
> > Note that the code there actually duplicates the current plane state,
> > updates the copy, swaps both states and then update the hardware based
> > on both new and old states, as the regular atomic commit flow would
> > do. With that, no reference counts are dropped until the old state
> > gets destroyed at the end of the function. Also note the if block that
> > handles the condition of (plane_state->fb && plane_state->fb !=
> > plane->state->fb) (plane_state is the old state after the swap).
> >
> >>> Of course to call it in its current shape, one needs to have a full
> >>> atomic state from a commit, after a flip, but we only have the new
> >>> plane state here. Perhaps you could duplicate existing state, update
> >>> the desired plane state, flip and then call vop_crtc_atomic_flush()?
> >> Could you please clarify your proposal? You mean duplicating
> >> plane->state ? I'm trying to see how this would fit it in the code.
> >> The drm_atomic_state structure at plate->state->state is actually always
> >> NULL (as an async update is applied right away).
> >>
> >>
> >>> Best regards,
> >>> Tomasz
> >>>
> >>  From your comment in v2:
> >>
> >>> Isn't this going to drop the old fb reference on the floor without
> >>> waiting for the hardware to actually stop scanning out from it?
> >> I've been trying to analyze this better, I also got some help from
> >> Gustavo Padovan, and I think there is no problem here as the
> >> configuration we are doing here will just be taken into consideration by
> >> the hardware in the next vblank, so I guess we can set and re-set
> >> plane->fb as much as we want.
> > The point here is not about setting and resetting the plane->fb
> > pointer. It's about what happens inside drm_atomic_set_fb_for_plane().
> >
> > It calls drm_framebuffer_get() for the new fb and
> > drm_framebuffer_put() for the old fb. In result, if the fb changes,
> > the old fb, which had its reference count incremented in the atomic
> > commit that set it to the plane before, has its reference count
> > decremented. Moreover, if the new reference count becomes 0,
> > drm_framebuffer_put() will immediately free the buffer.
> >
> > Freeing a buffer when the hardware is still scanning out of it isn't a
> > good idea, is it?
>
> My understanding is that in the async update path we never touch the fb
> that is still being scanned out - what you are referring as old fb. That
> is the design of async update. drm_atomic_set_fb_for_plane() replace
> pointers and refs between the fb we just received from userspace with
> the one on plane->state (that after the atomic swap holds the new state)
> which won't be scanned out until the next flip.

My understanding of async_update is that it is expected to instantly
program the hardware with the new plane state.

You can see that an async update can only happen if
drm_atomic_helper_async_check() succeeds:
https://github.com/freedesktop/drm-misc/blob/drm-misc-fixes/drivers/gpu/drm/drm_atomic_helper.c#L927

In turn drm_atomic_helper_async_check() succeeds only if all the
conditions are met:
1) No CRTC in the new state needs a modeset.
2) There is only one plane state in the new state.
3) The plane is not moved between CRTCs.
4) The plane ops include .atomic_async_update().
5) There is no fence attached to the new state.
6) Current plane state is already committed to hardware, i.e. the
hardware started scanning out according to that state.
(https://github.com/freedesktop/drm-misc/blob/drm-misc-fixes/drivers/gpu/drm/drm_atomic_helper.c#L1545)

Given that, the current plane state that the .atomic_async_update()
sees is the state that is currently used by the hardware. That in turn
means that the hardware is currently scanning out from the fb pointed
out by that state and care must be taken so that the access to it is
not taken away from the hardware until it switches to scanning out the
new fb.

> However I don't
> understand this part of the rockchip hardware, the fb is not the one
> being scanned out. Is this still a problem?

Given the above, I think this question doesn't hold anymore, right?

Best regards,
Tomasz

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