Message-ID: <CAPY8ntCbzFkbM5fZmo3RVw5okQkVKFcR8TCHOo+xkW7wNk8MQA@mail.gmail.com>
Date:   Mon, 21 Jun 2021 12:49:14 +0100
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Maxime Ripard <maxime@...no.tech>, Marek Vasut <marex@...x.de>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        LKML <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Eric Anholt <eric@...olt.net>,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        Phil Elwell <phil@...pberrypi.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] drm/vc4: dsi: Only register our component once a DSI
 device is attached

Hi Laurent

On Sun, 20 Jun 2021 at 23:49, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Dave,
>
> On Sun, Jun 20, 2021 at 09:42:27PM +0300, Laurent Pinchart wrote:
> > On Sun, Jun 20, 2021 at 03:29:03PM +0100, Dave Stevenson wrote:
> > > On Sun, 20 Jun 2021 at 04:26, Laurent Pinchart wrote:
> > > >
> > > > Hi Maxime,
> > > >
> > > > I'm testing this, and I'm afraid it causes an issue with all the
> > > > I2C-controlled bridges. I'm focussing on the newly merged ti-sn65dsi83
> > > > driver at the moment, but other are affected the same way.
> > > >
> > > > With this patch, the DSI component is only added when the DSI device is
> > > > attached to the host with mipi_dsi_attach(). In the ti-sn65dsi83 driver,
> > > > this happens in the bridge attach callback, which is called when the
> > > > bridge is attached by a call to drm_bridge_attach() in vc4_dsi_bind().
> > > > This creates a circular dependency, and the DRM/KMS device is never
> > > > created.
> > > >
> > > > How should this be solved ? Dave, I think you have shown an interest in
> > > > the sn65dsi83 recently, any help would be appreciated. On a side note,
> > > > I've tested the ti-sn65dsi83 driver on a v5.10 RPi kernel, without much
> > > > success (on top of commit e1499baa0b0c I get a very weird frame rate -
> > > > 147 fps of 99 fps instead of 60 fps - and nothing on the screen, and on
> > > > top of the latest v5.10 RPi branch, I get lock-related warnings at every
> > > > page flip), which is why I tried v5.12 and noticed this patch. Is it
> > > > worth trying to bring up the display on the v5.10 RPi kernel in parallel
> > > > to fixing the issue introduced in this patch, or is DSI known to be
> > > > broken there ?
> > >
> > > I've been looking at SN65DSI83/4, but as I don't have any hardware
> > > I've largely been suggesting things to try to those on the forums who
> > > do [1].
> > >
> > > My branch at https://github.com/6by9/linux/tree/rpi-5.10.y-sn65dsi8x-marek
> > > is the latest one I've worked on. It's rpi-5.10.y with Marek's driver
> > > cherry-picked, and an overlay and simple-panel definition by others.
> > > It also has a rework for vc4_dsi to use pm_runtime, instead of
> > > breaking up the DSI bridge chain (which is flawed as it never calls
> > > the bridge mode_set or mode_valid functions which sn65dsi83 relies
> > > on).
> > >
> > > I ran it on Friday in the lab and encountered an issue with vc4_dsi
> > > should vc4_dsi_encoder_mode_fixup wish for a divider of 7 (required
> > > for this 800x1280 panel over 4 lanes) where it resulted in an invalid
> > > mode configuration. That resulted in patch [2] which then gave me
> > > sensible numbers.
> > >
> > > That branch with dtoverlay=vc4-kms-v3d and
> > > dtoverlay=vc4-kms-dsi-ti-sn65dsi83 created all the expected devices,
> > > and everything came up normally.
> > > It was a busy day, but I think I even stuck a scope on the clock lanes
> > > at that point and confirmed that they were at the link frequency
> > > expected.
> >
> > Thanks, I'll test your branch and will report the results.
>
> I had to apply the following diff to work around a crash:
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> index 55b6c53207f5..647426aa793a 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> @@ -525,6 +525,9 @@ static bool sn65dsi83_mode_fixup(struct drm_bridge *bridge,
>
>         /* The DSI format is always RGB888_1X24 */
>         list_for_each_entry(connector, &ddev->mode_config.connector_list, head) {
> +               if (!connector->display_info.bus_formats)
> +                       continue;
> +
>                 switch (connector->display_info.bus_formats[0]) {
>                 case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
>                         ctx->lvds_format_24bpp = false;
>
> connector->display_info.bus_formats is NULL for the HDMI connectors, as
> I have nothing connected to them, as well as for the writeback
> connector.

I'm now confused as to what I'm doing as my branch appears NOT to have
Marek's latest version of the driver as it doesn't have
sn65dsi83_mode_fixup.
I need to have another look at what's going on - I think I've got
branches confused when switching between machines :-( Remaking that
branch now.

I do see that Marek has sent another patch around
sn65dsi83_mode_fixup, but it'll still dereference
connector->display_info.bus_formats[0] on all connectors. Shouldn't it
only be switching on the one connector that is connected to this
bridge, not HDMI or writeback connectors? I'm not totally clear on
which connectors are in that list.
https://patchwork.freedesktop.org/patch/440175/

> Then, when running kmstest --flip, I get one warning per frame:
>
> [   29.762089] [drm:vc4_dsi_runtime_resume] *ERROR* vc4_dsi_runtime_resume:
> [   29.763200] [drm:vc4_dsi_runtime_resume] *ERROR* vc4_dsi_runtime_resume: All good
> [   29.793861] ------------[ cut here ]------------
> [   29.798572] WARNING: CPU: 2 PID: 249 at drivers/gpu/drm/drm_modeset_lock.c:246 drm_modeset_lock+0xd0/0x100
> [   29.808365] Modules linked in: ipv6 bcm2835_codec(C) bcm2835_unicam bcm2835_v4l2(C) bcm2835_isp(C) bcm2835_mmal_vchiq(C) v4l2_mem2mem v4l2_dv_timings imx296 rtc_ds1307 videobuf2_vmallom
> [   29.855284] CPU: 2 PID: 249 Comm: kworker/u8:10 Tainted: G         C        5.10.44-v8+ #23
> [   29.863756] Hardware name: Raspberry Pi Compute Module 4 Rev 1.0 (DT)
> [   29.870297] Workqueue: events_unbound commit_work
> [   29.875077] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
> [   29.881172] pc : drm_modeset_lock+0xd0/0x100
> [   29.885506] lr : drm_atomic_get_new_or_current_crtc_state+0x6c/0x110
> [   29.891950] sp : ffffffc011fcbcb0
> [   29.895308] x29: ffffffc011fcbcb0 x28: ffffff80403fe780
> [   29.900705] x27: ffffff80415a2000 x26: ffffffc0106f0000
> [   29.906100] x25: 0000000000000000 x24: ffffff80420d3c80
> [   29.911495] x23: ffffff8042174080 x22: 0000000000000038
> [   29.916890] x21: 0000000000000000 x20: ffffff80421740a8
> [   29.922284] x19: ffffffc011f8bc50 x18: 0000000000000000
> [   29.927678] x17: 0000000000000000 x16: 0000000000000000
> [   29.933072] x15: 0000000000000000 x14: 0000000000000000
> [   29.938466] x13: 0048000000000329 x12: 0326032303290320
> [   29.943860] x11: 03200000020301f4 x10: 00000000000019e0
> [   29.949255] x9 : ffffffc0106efd8c x8 : ffffff804390d5c0
> [   29.954649] x7 : 7fffffffffffffff x6 : 0000000000000001
> [   29.960043] x5 : 0000000000000001 x4 : 0000000000000001
> [   29.965436] x3 : ffffff80415a2000 x2 : ffffff804199b200
> [   29.970830] x1 : 00000000000000bc x0 : ffffffc011f8bc98
> [   29.976225] Call trace:
> [   29.978708]  drm_modeset_lock+0xd0/0x100
> [   29.982687]  drm_atomic_get_new_or_current_crtc_state+0x6c/0x110
> [   29.988781]  vc4_atomic_complete_commit+0x4e4/0x860
> [   29.993729]  commit_work+0x18/0x20
> [   29.997181]  process_one_work+0x1c4/0x4a0
> [   30.001248]  worker_thread+0x50/0x420
> [   30.004965]  kthread+0x11c/0x150
> [   30.008239]  ret_from_fork+0x10/0x20
> [   30.011865] ---[ end trace f44ae6b09cda951a ]---
>
> Does it ring any bell ?

kmstest --flip is a new one on me. kmstest from
https://cgit.freedesktop.org/drm/libdrm/tree/tests/kmstest doesn't
have such an option.
Based on Google, I'm guessing at
https://github.com/tomba/kmsxx/blob/master/utils/kmstest.cpp. Multiple
apps with the same name is always fun.

> In case this is useful information, the problem didn't occur on top of
> commit e1499baa0b0c.

e1499baa0b0c is from back in March by the looks of it.
Maxime has done a number of reworks to accessor functions since then,
so it's quite possible there's a locking issue lurking. I'll let him
comment though.

  Dave

> > > Coming back to this patch though, it isn't in 5.10 so I'm not seeing
> > > the issues. As to the exact ordering of attaches, I can't claim
> > > sufficient knowledge on that front.
> > > I can try a cherry-pick of this patch to see what goes on, but it
> > > won't be for a day or two.
> >
> > Let's see if Maxime has an opinion :-)
> >
> > > [1] Largely https://www.raspberrypi.org/forums/viewtopic.php?f=44&t=305690,
> > > but ignore about the first 5 pages of the thread as different driver
> > > versions were floating about. Most stuff after that is based on
> > > Marek's driver.
> > > [2] https://github.com/6by9/linux/commit/c3c774136a1e946109048711d16974be8d520aaa
> > >
> > > > On Tue, Jul 07, 2020 at 12:19:12PM +0200, Maxime Ripard wrote:
> > > > > If the DSI driver is the last to probe, component_add will try to run all
> > > > > the bind callbacks straight away and return the error code.
> > > > >
> > > > > However, since we depend on a power domain, we're pretty much guaranteed to
> > > > > be in that case on the BCM2711, and are just lucky on the previous SoCs
> > > > > since the v3d also depends on that power domain and is further in the probe
> > > > > order.
> > > > >
> > > > > In that case, the DSI host will not stick around in the system: the DSI
> > > > > bind callback will be executed, will not find any DSI device attached and
> > > > > will return EPROBE_DEFER, and we will then remove the DSI host and ask to
> > > > > be probed later on.
> > > > >
> > > > > But since that host doesn't stick around, DSI devices like the RaspberryPi
> > > > > touchscreen whose probe is not linked to the DSI host (unlike the usual DSI
> > > > > devices that will be probed through the call to mipi_dsi_host_register)
> > > > > cannot attach to the DSI host, and we thus end up in a situation where the
> > > > > DSI host cannot probe because the panel hasn't probed yet, and the panel
> > > > > cannot probe because the DSI host hasn't yet.
> > > > >
> > > > > In order to break this cycle, let's wait until there's a DSI device that
> > > > > attaches to the DSI host to register the component and allow to progress
> > > > > further.
> > > > >
> > > > > Suggested-by: Andrzej Hajda <a.hajda@...sung.com>
> > > > > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> > > > > ---
> > > > >  drivers/gpu/drm/vc4/vc4_dsi.c | 25 ++++++++-----------------
> > > > >  1 file changed, 8 insertions(+), 17 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> > > > > index eaf276978ee7..19aab4e7e209 100644
> > > > > --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> > > > > +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> > > > > @@ -1246,10 +1246,12 @@ static ssize_t vc4_dsi_host_transfer(struct mipi_dsi_host *host,
> > > > >       return ret;
> > > > >  }
> > > > >
> > > > > +static const struct component_ops vc4_dsi_ops;
> > > > >  static int vc4_dsi_host_attach(struct mipi_dsi_host *host,
> > > > >                              struct mipi_dsi_device *device)
> > > > >  {
> > > > >       struct vc4_dsi *dsi = host_to_dsi(host);
> > > > > +     int ret;
> > > > >
> > > > >       dsi->lanes = device->lanes;
> > > > >       dsi->channel = device->channel;
> > > > > @@ -1284,6 +1286,12 @@ static int vc4_dsi_host_attach(struct mipi_dsi_host *host,
> > > > >               return 0;
> > > > >       }
> > > > >
> > > > > +     ret = component_add(&dsi->pdev->dev, &vc4_dsi_ops);
> > > > > +     if (ret) {
> > > > > +             mipi_dsi_host_unregister(&dsi->dsi_host);
> > > > > +             return ret;
> > > > > +     }
> > > > > +
> > > > >       return 0;
> > > > >  }
> > > > >
> > > > > @@ -1662,7 +1670,6 @@ static int vc4_dsi_dev_probe(struct platform_device *pdev)
> > > > >  {
> > > > >       struct device *dev = &pdev->dev;
> > > > >       struct vc4_dsi *dsi;
> > > > > -     int ret;
> > > > >
> > > > >       dsi = devm_kzalloc(dev, sizeof(*dsi), GFP_KERNEL);
> > > > >       if (!dsi)
> > > > > @@ -1670,26 +1677,10 @@ static int vc4_dsi_dev_probe(struct platform_device *pdev)
> > > > >       dev_set_drvdata(dev, dsi);
> > > > >
> > > > >       dsi->pdev = pdev;
> > > > > -
> > > > > -     /* Note, the initialization sequence for DSI and panels is
> > > > > -      * tricky.  The component bind above won't get past its
> > > > > -      * -EPROBE_DEFER until the panel/bridge probes.  The
> > > > > -      * panel/bridge will return -EPROBE_DEFER until it has a
> > > > > -      * mipi_dsi_host to register its device to.  So, we register
> > > > > -      * the host during pdev probe time, so vc4 as a whole can then
> > > > > -      * -EPROBE_DEFER its component bind process until the panel
> > > > > -      * successfully attaches.
> > > > > -      */
> > > > >       dsi->dsi_host.ops = &vc4_dsi_host_ops;
> > > > >       dsi->dsi_host.dev = dev;
> > > > >       mipi_dsi_host_register(&dsi->dsi_host);
> > > > >
> > > > > -     ret = component_add(&pdev->dev, &vc4_dsi_ops);
> > > > > -     if (ret) {
> > > > > -             mipi_dsi_host_unregister(&dsi->dsi_host);
> > > > > -             return ret;
> > > > > -     }
> > > > > -
> > > > >       return 0;
> > > > >  }
> > > > >
>
> --
> Regards,
>
> Laurent Pinchart

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