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

[Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>]

On 11/03/2023 23:53, Adam Ford wrote:
> On Sat, Mar 11, 2023 at 3:40 PM Dmitry Baryshkov
> <dmitry.baryshkov@xxxxxxxxxx> wrote:
> > "Hi Abhinav,
> >
> > On Sat, 11 Mar 2023 at 23:18, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:
> > > 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.
>
> Thanks to both of you for the ideas.
>
> > I went on and looked into the adv7533 datasheet. Strangely enough
> > these conditions do not correspond to the limitations from the
> > datasheet:
> > - "pixel clocks of up to 80 MHz",
> > - "each [DSI lane] running up to 800 Mbps"
> >
> > So probably the conditions should be as following:
> >
> > if (mode->clock > 80000)
> >     return MODE_CLOCK_HIGH;
>
> This is consistent with what is happening on the 7511.
>
> > if (mode->clock * bpp > 800000 * adv->num_dsi_lanes)
> >      return MODE_CLOCK_HIGH;
> >
> > See https://www.analog.com/media/en/technical-documentation/data-sheets/adv7533.pdf
>
> These numbers would need to be changed for the 7535, the device I am
> using.  So I'll submit a patch which checks these with different max
> values depending on whether or not the device is 7533 or 7535.

For adv7535 the max pixel clock seems to 148.5 MHz, max lane clock is 
891 MHz.

I'm slightly confused about adv7511, whose datasheet contains just a 
single number of '225 MHz'.

> adam
>
> > > > > > -       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.
> >
> >
> >
> > --
> > With best wishes
> > Dmitry

--
With best wishes
Dmitry