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.
>
> 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
