Re: [PATCH v2] drm/bridge: adv7533: remove dynamic lane switching from adv7533 bridge

[Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>]

Hi Adam

On 3/11/2023 9:28 AM, Adam Ford wrote:
> On Thu, Oct 13, 2022 at 3:39 AM Robert Foss <robert.foss@xxxxxxxxxx> wrote:
> > On Tue, 11 Oct 2022 at 23:11, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:
> > > adv7533 bridge tries to dynamically switch lanes based on the
> > > mode by detaching and attaching the mipi dsi device.
> > >
> > > This approach is incorrect because this method of dynamic switch of
> > > detaching and attaching the mipi dsi device also results in removing
> > > and adding the component which is not necessary.
> > >
> > > This approach is also prone to deadlocks. So for example, on the
> > > db410c whenever this path is executed with lockdep enabled,
> > > this results in a deadlock due to below ordering of locks.
> > >
> > > -> #1 (crtc_ww_class_acquire){+.+.}-{0:0}:
> > >          lock_acquire+0x6c/0x90
> > >          drm_modeset_acquire_init+0xf4/0x150
> > >          drmm_mode_config_init+0x220/0x770
> > >          msm_drm_bind+0x13c/0x654
> > >          try_to_bring_up_aggregate_device+0x164/0x1d0
> > >          __component_add+0xa8/0x174
> > >          component_add+0x18/0x2c
> > >          dsi_dev_attach+0x24/0x30
> > >          dsi_host_attach+0x98/0x14c
> > >          devm_mipi_dsi_attach+0x38/0xb0
> > >          adv7533_attach_dsi+0x8c/0x110
> > >          adv7511_probe+0x5a0/0x930
> > >          i2c_device_probe+0x30c/0x350
> > >          really_probe.part.0+0x9c/0x2b0
> > >          __driver_probe_device+0x98/0x144
> > >          driver_probe_device+0xac/0x14c
> > >          __device_attach_driver+0xbc/0x124
> > >          bus_for_each_drv+0x78/0xd0
> > >          __device_attach+0xa8/0x1c0
> > >          device_initial_probe+0x18/0x24
> > >          bus_probe_device+0xa0/0xac
> > >          deferred_probe_work_func+0x90/0xd0
> > >          process_one_work+0x28c/0x6b0
> > >          worker_thread+0x240/0x444
> > >          kthread+0x110/0x114
> > >          ret_from_fork+0x10/0x20
> > >
> > > -> #0 (component_mutex){+.+.}-{3:3}:
> > >          __lock_acquire+0x1280/0x20ac
> > >          lock_acquire.part.0+0xe0/0x230
> > >          lock_acquire+0x6c/0x90
> > >          __mutex_lock+0x84/0x400
> > >          mutex_lock_nested+0x3c/0x70
> > >          component_del+0x34/0x170
> > >          dsi_dev_detach+0x24/0x30
> > >          dsi_host_detach+0x20/0x64
> > >          mipi_dsi_detach+0x2c/0x40
> > >          adv7533_mode_set+0x64/0x90
> > >          adv7511_bridge_mode_set+0x210/0x214
> > >          drm_bridge_chain_mode_set+0x5c/0x84
> > >          crtc_set_mode+0x18c/0x1dc
> > >          drm_atomic_helper_commit_modeset_disables+0x40/0x50
> > >          msm_atomic_commit_tail+0x1d0/0x6e0
> > >          commit_tail+0xa4/0x180
> > >          drm_atomic_helper_commit+0x178/0x3b0
> > >          drm_atomic_commit+0xa4/0xe0
> > >          drm_client_modeset_commit_atomic+0x228/0x284
> > >          drm_client_modeset_commit_locked+0x64/0x1d0
> > >          drm_client_modeset_commit+0x34/0x60
> > >          drm_fb_helper_lastclose+0x74/0xcc
> > >          drm_lastclose+0x3c/0x80
> > >          drm_release+0xfc/0x114
> > >          __fput+0x70/0x224
> > >          ____fput+0x14/0x20
> > >          task_work_run+0x88/0x1a0
> > >          do_exit+0x350/0xa50
> > >          do_group_exit+0x38/0xa4
> > >          __wake_up_parent+0x0/0x34
> > >          invoke_syscall+0x48/0x114
> > >          el0_svc_common.constprop.0+0x60/0x11c
> > >          do_el0_svc+0x30/0xc0
> > >          el0_svc+0x58/0x100
> > >          el0t_64_sync_handler+0x1b0/0x1bc
> > >          el0t_64_sync+0x18c/0x190
> > >
> > > Due to above reasons, remove the dynamic lane switching
> > > code from adv7533 bridge chip and filter out the modes
> > > which would need different number of lanes as compared
> > > to the initialization time using the mode_valid callback.
> > >
> > > This can be potentially re-introduced by using the pre_enable()
> > > callback but this needs to be evaluated first whether such an
> > > approach will work so this will be done with a separate change.
> > >
> > > changes since RFC:
> > >          - Fix commit text and add TODO comment
> > >
> > > changes in v2:
> > >          - Fix checkpatch formatting errors
> > >
> > > Fixes: 62b2f026cd8e ("drm/bridge: adv7533: Change number of DSI lanes dynamically")
> > > Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/16
> > > Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > > Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > > Reviewed-by: Robert Foss <robert.foss@xxxxxxxxxx>
> > > Link: https://lore.kernel.org/r/1661797363-7564-1-git-send-email-quic_abhinavk@xxxxxxxxxxx
> > > ---
> > >   drivers/gpu/drm/bridge/adv7511/adv7511.h     |  3 ++-
> > >   drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 18 ++++++++++++++----
> > >   drivers/gpu/drm/bridge/adv7511/adv7533.c     | 25 +++++++++++++------------
> > >   3 files changed, 29 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511.h b/drivers/gpu/drm/bridge/adv7511/adv7511.h
> > > index a031a0cd1f18..1053d185b24c 100644
> > > --- a/drivers/gpu/drm/bridge/adv7511/adv7511.h
> > > +++ b/drivers/gpu/drm/bridge/adv7511/adv7511.h
> > > @@ -405,7 +405,8 @@ static inline int adv7511_cec_init(struct device *dev, struct adv7511 *adv7511)
> > >
> > >   void adv7533_dsi_power_on(struct adv7511 *adv);
> > >   void adv7533_dsi_power_off(struct adv7511 *adv);
> > > -void adv7533_mode_set(struct adv7511 *adv, const struct drm_display_mode *mode);
> > > +enum drm_mode_status adv7533_mode_valid(struct adv7511 *adv,
> > > +                                       const struct drm_display_mode *mode);
> > >   int adv7533_patch_registers(struct adv7511 *adv);
> > >   int adv7533_patch_cec_registers(struct adv7511 *adv);
> > >   int adv7533_attach_dsi(struct adv7511 *adv);
> > > diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > > index 38bf28720f3a..4bc7aac94a16 100644
> > > --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > > +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > > @@ -697,7 +697,7 @@ adv7511_detect(struct adv7511 *adv7511, struct drm_connector *connector)
> > >   }
> > >
> > >   static enum drm_mode_status adv7511_mode_valid(struct adv7511 *adv7511,
> > > -                             struct drm_display_mode *mode)
> > > +                             const struct drm_display_mode *mode)
> > >   {
> > >          if (mode->clock > 165000)
> > >                  return MODE_CLOCK_HIGH;
> > > @@ -791,9 +791,6 @@ static void adv7511_mode_set(struct adv7511 *adv7511,
> > >          regmap_update_bits(adv7511->regmap, 0x17,
> > >                  0x60, (vsync_polarity << 6) | (hsync_polarity << 5));
> > >
> > > -       if (adv7511->type == ADV7533 || adv7511->type == ADV7535)
> > > -               adv7533_mode_set(adv7511, adj_mode);
> > > -
> > >          drm_mode_copy(&adv7511->curr_mode, adj_mode);
> > >
> > >          /*
> > > @@ -913,6 +910,18 @@ static void adv7511_bridge_mode_set(struct drm_bridge *bridge,
> > >          adv7511_mode_set(adv, mode, adj_mode);
> > >   }
> > >
> > > +static enum drm_mode_status adv7511_bridge_mode_valid(struct drm_bridge *bridge,
> > > +                                                     const struct drm_display_info *info,
> > > +               const struct drm_display_mode *mode)
> > > +{
> > > +       struct adv7511 *adv = bridge_to_adv7511(bridge);
> > > +
> > > +       if (adv->type == ADV7533 || adv->type == ADV7535)
> > > +               return adv7533_mode_valid(adv, mode);
> > > +       else
> > > +               return adv7511_mode_valid(adv, mode);
> > > +}
> > > +
> > >   static int adv7511_bridge_attach(struct drm_bridge *bridge,
> > >                                   enum drm_bridge_attach_flags flags)
> > >   {
> > > @@ -960,6 +969,7 @@ static const struct drm_bridge_funcs adv7511_bridge_funcs = {
> > >          .enable = adv7511_bridge_enable,
> > >          .disable = adv7511_bridge_disable,
> > >          .mode_set = adv7511_bridge_mode_set,
> > > +       .mode_valid = adv7511_bridge_mode_valid,
> > >          .attach = adv7511_bridge_attach,
> > >          .detect = adv7511_bridge_detect,
> > >          .get_edid = adv7511_bridge_get_edid,
> > > diff --git a/drivers/gpu/drm/bridge/adv7511/adv7533.c b/drivers/gpu/drm/bridge/adv7511/adv7533.c
> > > index ef6270806d1d..258c79d4dab0 100644
> > > --- a/drivers/gpu/drm/bridge/adv7511/adv7533.c
> > > +++ b/drivers/gpu/drm/bridge/adv7511/adv7533.c
> > > @@ -100,26 +100,27 @@ void adv7533_dsi_power_off(struct adv7511 *adv)
> > >          regmap_write(adv->regmap_cec, 0x27, 0x0b);
> > >   }
> > >
> > > -void adv7533_mode_set(struct adv7511 *adv, const struct drm_display_mode *mode)
> > > +enum drm_mode_status adv7533_mode_valid(struct adv7511 *adv,
> > > +                                       const struct drm_display_mode *mode)
> > >   {
> > > +       int lanes;
> > >          struct mipi_dsi_device *dsi = adv->dsi;
> > > -       int lanes, ret;
> > > -
> > > -       if (adv->num_dsi_lanes != 4)
> > > -               return;
> > >
> > >          if (mode->clock > 80000)
> > >                  lanes = 4;
> > >          else
> > >                  lanes = 3;
>
> I know this thread is a bit old, but I have an i.MX8M Mini with an
> adv7535 HDMI bridge, and I'm able to display video on a 4-lane
> interface with a clock as low as 27000.

Looks like this condition is not tracking how low the bridge can support 
with 4 lanes but how high you can support with 3 lanes. Thats the issue.

This condition has been this way since the original bridge driver:

drm/bridge: adv7533: Change number of DSI lanes dynamically

Yes, its possible that with 4 lanes you can support a lower rate but 
with 3 lanes you cannot support a higher one. So that needs to be handled.

The extra conditional's intention was to make sure that if you try to 
switch to a mode which has a different number of lanes than what was set 
in the device tree (basically dynamic mode switch) then fail that.

So perhaps this condition can be modified to :

if (num_dsi_lanes < 4 && mode->clock > 80000)
	return MODE_BAD;

I think that should fix your issue. You can set the number of lanes to 4 
for your board if it supports that using the DT node adi,dsi-lanes.

> > > -       if (lanes != dsi->lanes) {
> > > -               mipi_dsi_detach(dsi);
> > > -               dsi->lanes = lanes;
> > > -               ret = mipi_dsi_attach(dsi);
> > > -               if (ret)
> > > -                       dev_err(&dsi->dev, "failed to change host lanes\n");
> > > -       }
> > > +       /*
> > > +        * TODO: add support for dynamic switching of lanes
> > > +        * by using the bridge pre_enable() op . Till then filter
> > > +        * out the modes which shall need different number of lanes
> > > +        * than what was configured in the device tree.
> > > +        */
> > > +       if (lanes != dsi->lanes)
> > > +               return MODE_BAD;
> > > +
>
> My board doesn't currently support dynamic switching, but I'd like to
> keep 4-lanes all the time.  However, this return eliminates several
> resolutions that I can successfully display.
> I'd like to eliminate this error, so it works on the imx8m
> mini/nano/plus, but I am not sure the best approach without breaking
> someone else's board.
>  > I was thinking I could add a flag to disable dynamic switching.  If
> that flag is set, we'd return MODE_OK here.
>
> Does anyone have any suggestions on an apporach?
>
> adam

I am thinking of this solution

if (num_dsi_lanes < 4 && mode->clock > 80000)
	return MODE_BAD;

So lets say some user tried to set number of lanes to 3 but tries a mode 
needing > 80000 clock then fail.

That way we still dont support dynamic mode switch but also dont limit 
the modes which can be supported with 4 lanes.

> > > +       return MODE_OK;
> > >   }
> > >
> > >   int adv7533_patch_registers(struct adv7511 *adv)
> > > --
> > > 2.7.4
> >
> > Applied to drm-misc-next.