On Tue, 29 Aug 2023 at 22:09, Abhinav Kumar <quic_abhin...@quicinc.com> wrote:
>
>
>
> On 8/29/2023 11:51 AM, Dmitry Baryshkov wrote:
> > On Tue, 29 Aug 2023 at 20:22, Abhinav Kumar <quic_abhin...@quicinc.com>
> > wrote:
> >>
> >>
> >>
> >> On 8/29/2023 9:43 AM, Dmitry Baryshkov wrote:
> >>> On Tue, 29 Aug 2023 at 19:37, Abhinav Kumar <quic_abhin...@quicinc.com>
> >>> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 8/29/2023 2:26 AM, Dmitry Baryshkov wrote:
> >>>>> On Tue, 29 Aug 2023 at 12:22, <neil.armstr...@linaro.org> wrote:
> >>>>>>
> >>>>>> On 28/08/2023 19:07, Abhinav Kumar wrote:
> >>>>>>> Hi Neil
> >>>>>>>
> >>>>>>> Sorry I didnt respond earlier on this thread.
> >>>>>>>
> >>>>>>> On 8/28/2023 1:49 AM, neil.armstr...@linaro.org wrote:
> >>>>>>>> Hi Jessica,
> >>>>>>>>
> >>>>>>>> On 25/08/2023 20:37, Jessica Zhang wrote:
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On 8/21/2023 3:01 AM, neil.armstr...@linaro.org wrote:
> >>>>>>>>>> Hi Maxime,
> >>>>>>>>>>
> >>>>>>>>>> On 21/08/2023 10:17, Maxime Ripard wrote:
> >>>>>>>>>>> Hi,
> >>>>>>>>>>>
> >>>>>>>>>>> On Fri, Aug 18, 2023 at 10:25:48AM +0200,
> >>>>>>>>>>> neil.armstr...@linaro.org wrote:
> >>>>>>>>>>>> On 17/08/2023 20:35, Dmitry Baryshkov wrote:
> >>>>>>>>>>>>> On 16/08/2023 10:51, neil.armstr...@linaro.org wrote:
> >>>>>>>>>>>>>> Sending HS commands will always work on any controller, it's
> >>>>>>>>>>>>>> all
> >>>>>>>>>>>>>> about LP commands. The Samsung panels you listed only send HS
> >>>>>>>>>>>>>> commands so they can use prepare_prev_first and work on any
> >>>>>>>>>>>>>> controllers.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> I think there is some misunderstanding there, supported by the
> >>>>>>>>>>>>> description of the flag.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> If I remember correctly, some hosts (sunxi) can not send DCS
> >>>>>>>>>>>>> commands after enabling video stream and switching to HS mode,
> >>>>>>>>>>>>> see
> >>>>>>>>>>>>> [1]. Thus, as you know, most of the drivers have all DSI panel
> >>>>>>>>>>>>> setup
> >>>>>>>>>>>>> commands in drm_panel_funcs::prepare() /
> >>>>>>>>>>>>> drm_bridge_funcs::pre_enable() callbacks, not paying attention
> >>>>>>>>>>>>> whether these commands are to be sent in LP or in HS mode.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Previously DSI source drivers could power on the DSI link
> >>>>>>>>>>>>> either in
> >>>>>>>>>>>>> mode_set() or in pre_enable() callbacks, with mode_set() being
> >>>>>>>>>>>>> the
> >>>>>>>>>>>>> hack to make panel/bridge drivers to be able to send commands
> >>>>>>>>>>>>> from
> >>>>>>>>>>>>> their prepare() / pre_enable() callbacks.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> With the prev_first flags being introduced, we have established
> >>>>>>>>>>>>> that
> >>>>>>>>>>>>> DSI link should be enabled in DSI host's pre_enable() callback
> >>>>>>>>>>>>> and
> >>>>>>>>>>>>> switched to HS mode (be it command or video) in the enable()
> >>>>>>>>>>>>> callback.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> So far so good.
> >>>>>>>>>>>>
> >>>>>>>>>>>> It seems coherent, I would like first to have a state of all DSI
> >>>>>>>>>>>> host
> >>>>>>>>>>>> drivers and make this would actually work first before adding the
> >>>>>>>>>>>> prev_first flag to all the required panels.
> >>>>>>>>>>>
> >>>>>>>>>>> This is definitely what we should do in an ideal world, but at
> >>>>>>>>>>> least for
> >>>>>>>>>>> sunxi there's no easy way for it at the moment. There's no
> >>>>>>>>>>> documentation
> >>>>>>>>>>> for it and the driver provided doesn't allow this to happen.
> >>>>>>>>>>>
> >>>>>>>>>>> Note that I'm not trying to discourage you or something here, I'm
> >>>>>>>>>>> simply
> >>>>>>>>>>> pointing out that this will be something that we will have to
> >>>>>>>>>>> take into
> >>>>>>>>>>> account. And it's possible that other drivers are in a similar
> >>>>>>>>>>> situation.
> >>>>>>>>>>>
> >>>>>>>>>>>>> Unfortunately this change is not fully backwards-compatible.
> >>>>>>>>>>>>> This
> >>>>>>>>>>>>> requires that all DSI panels sending commands from prepare()
> >>>>>>>>>>>>> should
> >>>>>>>>>>>>> have the prepare_prev_first flag. In some sense, all such
> >>>>>>>>>>>>> patches
> >>>>>>>>>>>>> might have Fixes: 5ea6b1702781 ("drm/panel: Add
> >>>>>>>>>>>>> prepare_prev_first
> >>>>>>>>>>>>> flag to drm_panel").
> >>>>>>>>>>>>
> >>>>>>>>>>>> This kind of migration should be done *before* any possible
> >>>>>>>>>>>> regression, not the other way round.
> >>>>>>>>>>>>
> >>>>>>>>>>>> If all panels sending commands from prepare() should have the
> >>>>>>>>>>>> prepare_prev_first flag, then it should be first, check for
> >>>>>>>>>>>> regressions then continue.
> >>>>>>>>>>>>
> >>>>>>>>>>>> <snip>
> >>>>>>>>>>>>
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> I understand, but this patch doesn't qualify as a fix for
> >>>>>>>>>>>>>> 9e15123eca79 and is too late to be merged in drm-misc-next for
> >>>>>>>>>>>>>> v6.6, and since 9e15123eca79 actually breaks some support it
> >>>>>>>>>>>>>> should be reverted (+ deps) since we are late in the rc cycles.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> If we go this way, we can never reapply these patches. There
> >>>>>>>>>>>>> will be
> >>>>>>>>>>>>> no guarantee that all panel drivers are completely converted. We
> >>>>>>>>>>>>> already have a story without an observable end -
> >>>>>>>>>>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR.
> >>>>>>>>>>>>
> >>>>>>>>>>>> I don't understand this point, who would block re-applying the
> >>>>>>>>>>>> patches ?
> >>>>>>>>>>>>
> >>>>>>>>>>>> The migration to DRM_BRIDGE_ATTACH_NO_CONNECTOR was done over
> >>>>>>>>>>>> multiple
> >>>>>>>>>>>> Linux version and went smoothly because we reverted regressing
> >>>>>>>>>>>> patches
> >>>>>>>>>>>> and restarted when needed, I don't understand why we can't do
> >>>>>>>>>>>> this
> >>>>>>>>>>>> here aswell.
> >>>>>>>>>>>>
> >>>>>>>>>>>>> I'd consider that the DSI driver is correct here and it is
> >>>>>>>>>>>>> about the
> >>>>>>>>>>>>> panel drivers that require fixes patches. If you care about the
> >>>>>>>>>>>>> particular Fixes tag, I have provided one several lines above.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Unfortunately it should be done in the other way round, prepare
> >>>>>>>>>>>> for
> >>>>>>>>>>>> migration, then migrate,
> >>>>>>>>>>>>
> >>>>>>>>>>>> I mean if it's a required migration, then it should be done and
> >>>>>>>>>>>> I'll
> >>>>>>>>>>>> support it from both bridge and panel PoV.
> >>>>>>>>>>>>
> >>>>>>>>>>>> So, first this patch has the wrong Fixes tag, and I would like a
> >>>>>>>>>>>> better explanation on the commit message in any case. Then I
> >>>>>>>>>>>> would
> >>>>>>>>>>>> like to have an ack from some drm-misc maintainers before
> >>>>>>>>>>>> applying it
> >>>>>>>>>>>> because it fixes a patch that was sent via the msm tree thus per
> >>>>>>>>>>>> the
> >>>>>>>>>>>> drm-misc rules I cannot apply it via the drm-misc-next-fixes
> >>>>>>>>>>>> tree.
> >>>>>>>>>>>
> >>>>>>>>>>> Sorry, it's not clear to me what you'd like our feedback on
> >>>>>>>>>>> exactly?
> >>>>>>>>>>
> >>>>>>>>>> So let me resume the situation:
> >>>>>>>>>>
> >>>>>>>>>> - pre_enable_prev_first was introduced in [1]
> >>>>>>>>>> - some panels made use of pre_enable_prev_first
> >>>>>>>>>> - Visionox VTDR6130 was enabled on SM8550 systems and works on
> >>>>>>>>>> v6.5 kernels and before
> >>>>>>>>>> - patch [2] was introduced on MSM DRM tree, breaking VTDR6130 on
> >>>>>>>>>> SM8550 systems (and probably other Video mode panels on Qcom
> >>>>>>>>>> platforms)
> >>>>>>>>>> - this fix was sent late, and is now too late to be merged via
> >>>>>>>>>> drm-misc-next
> >>>>>>>>>
> >>>>>>>>> Hi Neil and Maxime,
> >>>>>>>>>
> >>>>>>>>> I agree with Neil that 9e15123eca79 was the commit that introduced
> >>>>>>>>> the issue (since it changed the MSM DSI host behavior).
> >>>>>>>>>
> >>>>>>>>> However, I'm not too keen on simply reverting that patch because
> >>>>>>>>>
> >>>>>>>>> 1) it's not wrong to have the dsi_power_on in pre_enable. Arguably,
> >>>>>>>>> it actually makes more sense to power on DSI host in pre_enable
> >>>>>>>>> than in modeset (since modeset is meant for setting the bridge
> >>>>>>>>> mode), and
> >>>>>>>>
> >>>>>>>> I never objected that, it's the right path to go.
> >>>>>>>>
> >>>>>>>
> >>>>>>> Ack.
> >>>>>>>
> >>>>>>>>>
> >>>>>>>>> 2) I think it would be good practice to keep specific bridge chip
> >>>>>>>>> checks out of the DSI host driver.
> >>>>>>>>
> >>>>>>>> We discussed about a plan with Maxime and Dmitry about that, and it
> >>>>>>>> would require adding
> >>>>>>>> a proper atomic panel API to handle a "negociation" with the host
> >>>>>>>> controller.
> >>>>>>>>
> >>>>>>>
> >>>>>>> May I know what type of negotiation is needed here?
> >>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> That being said, what do you think about setting the default value
> >>>>>>>>> of prepare_prev_first to true (possibly in panel_bridge_attach)?
> >>>>>>>>
> >>>>>>>> As Dmitry pointed, all panels sending LP commands in pre_enable()
> >>>>>>>> should have prepare_prev_first to true.
> >>>>>>>>
> >>>>>>>
> >>>>>>> I wanted to respond to this earlier but didnt get a chance.
> >>>>>>>
> >>>>>>> From the documentation of this flag, this has nothing to do
> >>>>>>> whether panels are sending the LP commands (commands sent in LP mode)
> >>>>>>> OR HS commands (commands sent in HS mode).
> >>>>>>>
> >>>>>>> This is more about sending the commands whether the lanes are in LP11
> >>>>>>> state before sending the ON commands.
> >>>>>>>
> >>>>>>> 195 * The previous controller should be prepared first, before
> >>>>>>> the prepare
> >>>>>>> 196 * for the panel is called. This is largely required for DSI
> >>>>>>> panels
> >>>>>>> 197 * where the DSI host controller should be initialised to
> >>>>>>> LP-11 before
> >>>>>>> 198 * the panel is powered up.
> >>>>>>> 199 */
> >>>>>>> 200 bool prepare_prev_first;
> >>>>>>>
> >>>>>>> These are conceptually different and thats what I explained Dmitry in
> >>>>>>> our call.
> >>>>>>>
> >>>>>>> Sending ON commands in LP11 state is a requirement I have seen with
> >>>>>>> many panels and its actually the right expectation as well to send
> >>>>>>> the commands when the lanes are in a well-defined LP11 state.
> >>>>>>>
> >>>>>>> From the panels which I have seen, the opposite is never true (OR
> >>>>>>> i have never seen it this way).
> >>>>>>>
> >>>>>>> The parade chip was the only exception and that issue was never
> >>>>>>> root-caused leading us to have bridge specific handling in MSM driver.
> >>>>>>>
> >>>>>>> In other words, it would be very unlikely that a panel should be
> >>>>>>> broken or shouldn't work when the ON commands are sent when the lanes
> >>>>>>> are in LP11 state.
> >>>>>>>
> >>>>>>> So I agree with Jessica, that we should set the default value of this
> >>>>>>> flag to true in the framework so that only the bridges/panels which
> >>>>>>> need this to be false do that explicitly. From the examples I pointed
> >>>>>>> out including MTK, even those vendors are powering on their DSI in
> >>>>>>> pre_enable() which means none of these panels will work there too.
> >>>>>>>
> >>>>>>>>>
> >>>>>>>>> It seems to me that most panel drivers send DCS commands during
> >>>>>>>>> pre_enable, so maybe it would make more sense to power on DSI host
> >>>>>>>>> before panel enable() by default. Any panel that needs DSI host to
> >>>>>>>>> be powered on later could then explicitly set the flag to false in
> >>>>>>>>> their respective drivers.
> >>>>>>>>
> >>>>>>>> A proper migration should be done, yes, but not as a fix on top of
> >>>>>>>> v6.5.
> >>>>>>>>
> >>>>>>>
> >>>>>>> I am fine to drop this fix in favor of making the prepare_prev_first
> >>>>>>> as default true but we need an agreement first. From what I can see,
> >>>>>>> parade chip will be the only one which will need this to be set to
> >>>>>>> false and we can make that change.
> >>>>>>>
> >>>>>>> Let me know if this works as a migration plan.
> >>>>>>
> >>>>>> Yep agreed, let's do this
> >>>>>>
> >>>>>> The panel's prepare_prev_first should be reversed to something like
> >>>>>> not_prepare_prev_first to make it an exception.
> >>>>>
> >>>>> This will break all non-DSI panels, which might depend on the current
> >>>>> bridge calling order.
> >>>>>
> >>>>> I started looking at the explicit DSI power up sequencing, but it will
> >>>>> take a few more days to mature.
> >>>>>
> >>>>
> >>>> May I know why this would break all non-DSI panels?
> >>>
> >>> Existing panel drivers might be depending on the init order. Do we
> >>> know for sure that none of DPI panels will be broken if there is a
> >>> video stream ongoing during the reset procedure?
> >>> Or the panel-edp, which I'm pretty sure will require
> >>> not_prepare_prev_first.
> >>>
> >>
> >> Can you please explain why would video stream be ON in pre_enable()?
> >>
> >> Even though we call msm_dsi_host_enable() in the DSI's pre_enable(), the
> >> timing engine is not enabled until the encoder's enable and the first
> >> commit after that so video stream wont be sent till then.
> >
> > You are describing the MSM DSI case. I was pointing to the fact that
> > parent's pre_enable if called too early might conflict with the next
> > bridge driver in the _generic_ case. E.g. eDP or DPI. Even if is not a
> > full-featured video stream, this state might confuse the panel. So we
> > can not blindly switch the order of pre_enable callbacks for the
> > bridge-panel pair.
> >
>
> Even if the end connector was a eDP or DPI, the input to the bridge was
> DSI so I think its unlikely that video stream was on before encoder's
> enable but I cannot speak for all these interfaces/vendors.
>
> So, to accommodate both worlds, does this work?
>
> diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
> index 9316384b4474..2b38388d4e56 100644
> --- a/drivers/gpu/drm/bridge/panel.c
> +++ b/drivers/gpu/drm/bridge/panel.c
> @@ -416,7 +416,10 @@ struct drm_bridge
> *devm_drm_panel_bridge_add_typed(struct device *dev,
> return bridge;
> }
>
> - bridge->pre_enable_prev_first = panel->prepare_prev_first;
> + if (connector_type == DRM_MODE_CONNECTOR_DSI)
> + bridge->pre_enable_prev_first = true;
> + else
> + bridge->pre_enable_prev_first = panel->prepare_prev_first;
looks like a hack.
>
> *ptr = bridge;
> devres_add(dev, ptr);
>
> >>
> >> drm_atomic_bridge_chain_pre_enable() is called before the encoder's enable.
> >>
> >> drm_atomic_bridge_chain_enable() is the one which is called after the
> >> encoder's enable().
> >>
> >>>>
> >>>> Like I said, we dont know the full details of the parade issue but I do
> >>>> not see any reason why powering on a bridge chip with the DSI lanes
> >>>> being in proper LP11 state should cause an issue. Its a well defined and
> >>>> documented state in DSI spec.
> >>>>
> >>>> On the contrary, trying to turn on a bridge chip before powering on a
> >>>> controller could have more issues as we do not know what state the lanes
> >>>> are in when the MIPI devices (panel or bridge) are powered up.
> >>>>
> >>>> This sets the expectation and handshake straight.
> >>>
> >>>
> >
> >
> >
--
With best wishes
Dmitry
