[Freedreno] [RFT PATCH 2/2] drm/msm/dsi: Stop unconditionally powering up DSI hosts at modeset

[Abhinav Kumar]

On 1/27/2023 2:33 PM, Doug Anderson wrote:
> Hi,
> 
> On Fri, Jan 27, 2023 at 10:54 AM Abhinav Kumar
> <quic_abhinavk at quicinc.com> wrote:
>>
>> On 1/13/2023 3:56 PM, Douglas Anderson wrote:
>>> In commit 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to modeset
>>> time"), we moved powering up DSI hosts to modeset time. This wasn't
>>> because it was an elegant design, but there were no better options.
>>>
>>> That commit actually ended up breaking ps8640, and thus was born
>>> commit ec7981e6c614 ("drm/msm/dsi: don't powerup at modeset time for
>>> parade-ps8640") as a temporary hack to un-break ps8640 by moving it to
>>> the old way of doing things. It turns out that ps8640 _really_ doesn't
>>> like its pre_enable() function to be called after
>>> dsi_mgr_bridge_power_on(). Specifically (from experimentation, not
>>> because I have any inside knowledge), it looks like the assertion of
>>> "RST#" in the ps8640 runtime resume handler seems like it's not
>>> allowed to happen after dsi_mgr_bridge_power_on()
>>>
>>> Recently, Dave Stevenson's series landed allowing bridges some control
>>> over pre_enable ordering. The meaty commit for our purposes is commit
>>> 4fb912e5e190 ("drm/bridge: Introduce pre_enable_prev_first to alter
>>> bridge init order"). As documented by that series, if a bridge doesn't
>>> set "pre_enable_prev_first" then we should use the old ordering.
>>>
>>> Now that we have the commit ("drm/bridge: tc358762: Set
>>> pre_enable_prev_first") we can go back to the old ordering, which also
>>> allows us to remove the ps8640 special case.
>>>
>>> One last note is that even without reverting commit 7d8e9a90509f
>>> ("drm/msm/dsi: move DSI host powerup to modeset time"), if you _just_
>>> revert the ps8640 special case and try it out then it doesn't seem to
>>> fail anymore. I spent time bisecting / debugging this and it turns out
>>> to be mostly luck, so we still want this patch to make sure it's
>>> solid. Specifically the reason it sorta works these days is because
>>> we implemented wait_hpd_asserted() in ps8640 now, plus the magic of
>>> "pm_runtime" autosuspend. The fact that we have wait_hpd_asserted()
>>> implemented means that we actually power the bridge chip up just a wee
>>> bit earlier and then the bridge happens to stay on because of
>>> autosuspend and thus ends up powered before dsi_mgr_bridge_power_on().
>>>
>>> Cc: Dave Stevenson <dave.stevenson at raspberrypi.com>
>>> Cc: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
>>> Cc: Abhinav Kumar <quic_abhinavk at quicinc.com>
>>> Signed-off-by: Douglas Anderson <dianders at chromium.org>
>>
>> Why is the patch title showing 2/2? I am not seeing any 1/2 here.
> 
> Is it a problem with your mail filters? You can see it at:
> 
> https://lore.kernel.org/r/20230113155547.RFT.1.I723a3761d57ea60c5dd754c144aed6c3b2ea6f5a@changeid/
> 
> You are listed on the "To:" line. ;-)

Ah, I see what happened. The first patch did not have freedreno CCed but 
the second one did.

So freedreno PW got confused thinking , hey where is the first patch? :)

https://patchwork.freedesktop.org/series/112824/

And so did I :)

Perhaps freedreno should be CCed on both patches because its a series.

> 
> 
>>> @@ -349,7 +297,16 @@ static void dsi_mgr_bridge_pre_enable(struct drm_bridge *bridge)
>>>    host1_en_fail:
>>>        msm_dsi_host_disable(host);
>>>    host_en_fail:
>>> -
>>> +     msm_dsi_host_disable_irq(host);
>>> +     if (is_bonded_dsi && msm_dsi1) {
>>> +             msm_dsi_host_disable_irq(msm_dsi1->host);
>>> +             msm_dsi_host_power_off(msm_dsi1->host);
>>> +     }
>>
>> In addition to Dmitry's comment of keeping the bridge_power_on() name,
>>
>> this part of the change seems independent of the patch. This was missing
>> cleanup for DSI1 (esp the disable_irq part).
>>
>> So can we break it up into two parts.
>>
>> 1) Add missing cleanup for DSI1
>> 2) Just get rid of dsi_mgr_power_on_early() and keep the call
>> dsi_mgr_bridge_power_on() in dsi_mgr_bridge_pre_enable() unconditionally.
> 
> I didn't intentionally fix any bug in my patch--I just reverted it all
> back to how it was before. ;-)
> 
No sure what I am missing here but I certainly dont see 
msm_dsi_host_disable_irq() being part of any error handling labels which 
made me think you fixed that.

> So looking more closely, it looks like overall the current code (AKA
> what's landed today and without ${SUBJECT} patch) doesn't really
> handle errors with dsi_mgr_bridge_power_on() very well. The normal
> case of calling dsi_mgr_bridge_power_on() from modeset is totally
> ignored because modeset returns no error. Then the special workaround
> for ps8640 just followed the same pattern and assumed that
> dsi_mgr_bridge_power_on() succeeded. It also assumed that if the rest
> of dsi_mgr_bridge_pre_enable() failed that it didn't need to undo
> dsi_mgr_bridge_power_on() because it wouldn't have undone it in the
> modeset case.
> 

Yes thats right.

> While the current code isn't the best, it's not like the pre_enable()
> call could have returned errors anyway. It probably wasn't truly the
> end of the world to behave the way it did.
> 
> With all that, I guess my plan would be to do as Dmitry says and just
> always call dsi_mgr_bridge_power_on() from
> dsi_mgr_bridge_pre_enable(). In the first patch I'll just do that and
> remove the ps8640 workaround. Then I can add a 2nd patch that improves
> the error handling by having dsi_mgr_bridge_power_on() return an error
> code and then adding a matching dsi_mgr_bridge_power_off() that will
> undo it and include the extra cleanup.
> 

Sounds good to me.

> -Doug