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SubjectRe: [PATCH] drm/vc4: dsi: Only register our component once a DSI device is attached
Hi Laurent

On Fri, 2 Jul 2021 at 17:47, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Dave,
>
> On Mon, Jun 21, 2021 at 04:59:51PM +0300, Laurent Pinchart wrote:
> > On Mon, Jun 21, 2021 at 04:09:05PM +0300, Laurent Pinchart wrote:
> > > On Mon, Jun 21, 2021 at 03:56:16PM +0300, Laurent Pinchart wrote:
> > > > On Mon, Jun 21, 2021 at 12:49:14PM +0100, Dave Stevenson wrote:
> > > > > On Sun, 20 Jun 2021 at 23:49, Laurent Pinchart wrote:
> > > > > > 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've looked at that, and I'm afraid it doesn't go in the right
> > direction. The drm_encoder.crtc field is deprecated and documented as
> > only meaningful for non-atomic drivers. You're not introducing its
> > usage, but moving the configuration code from .enable() to the runtime
> > PM resume handler will make it impossible to fix this. The driver should
> > instead move to the .atomic_enable() function. If you need
> > enable/pre_enable in the DSI encoder, then you should turn it into a
> > drm_bridge.
>
> Is this something you're looking at by any chance ? I'm testing the
> ti-sn65dsi83 driver with VC4. I've spent a couple of hours debugging,
> only to realise that the vc4_dsi driver (before the rework you mention
> above) doesn't call .mode_set() on the bridges... Applying my sn65dsi83
> series that removes .mode_set() didn't help much as vc4_dsi doesn't call
> the atomic operations either :-) I'll test your branch now.

This is one of the reasons for my email earlier today - thank you for
your reply.

The current mainline vc4_dsi driver deliberately breaks the bridge
chain so that it gets called before the panel/bridge pre_enable and
can power everything up, therefore pre_enable can call host_transfer
to configure the panel/bridge over the DSI interface.
However we've both noted that it doesn't forward on the mode_set and
mode_valid calls, and my investigations say that it doesn't have
enough information to make those calls.

My branch returns the chain to normal, and tries to use pm_runtime to
power up the PHY at the first usage (host_transfer or _enable). The
PHY enable needs to know the link frequency to use, hence my question
over how that should be determined.
Currently it's coming from drm_encoder.crtc, but you say that's
deprecated. If a mode hasn't been set then we have no clock
information and bad things will happen.

On the Pi forums one person has DSI83 working with an 800x1280 panel
(Google Nexus 7 Gen 1 AIUI) using my branch, but only on 3 lanes
rather than 4. I have a suspicion it's because the mode_fixup for
burst mode has moved the panel timings too far outside the panel's
spec, hence my other question about how bridges should pick up the
panel timings independent of burst mode timings. The SN65DSI83 driver
currently programs the output LVDS side with the DSI timings and
doesn't account for burst mode.

If you want a call or to discuss your setup in more detail, then give
me a shout.
We have a DSI analyser on order now (3-4 week lead time), so hopefully
I'll soon be able to get some better visibility of what the block is
doing.

Dave

> > > > > > > > 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.
> >
> > I have that commit in my branch, but still get 125 fps instead of 60 fps
> > with kmstest --flip (after reverting commit 1c3834201272 "drm/vc4:
> > Increase the core clock based on HVS load"). I'm not sure if [2] is the
> > cause of this, but there seems to be an improvement: in my previous
> > tests, the mode was fixed up every time I would start the application,
> > with the timings getting more and more bizarre at every run :-)
> >
> > > > > > > > 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/
> > > >
> > > > The following series should fix the issue:
> > > >
> > > > [PATCH] drm/bridge: ti-sn65dsi83: Replace connector format patching with atomic_get_input_bus_fmts
> > > > [PATCH 0/5] ti-sn65dsi83: Finalize transition to atomic operations
> > > >
> > > > > > 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.
> > > >
> > > > Correct.
> > > >
> > > > > > 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.
> > > >
> > > > Maybe there's a reason why the patch the introduced
> > > > drm_atomic_get_new_or_current_crtc_state() in your branch hasn't made it
> > > > to mainline yet :-)
> > >
> > > Any chance this could be reverted from the RPi kernel v5.10 branch in
> > > the meantime ?
> > >
> > > > > > > > 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@samsung.com>
> > > > > > > > > > Signed-off-by: Maxime Ripard <maxime@cerno.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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