Re: [PATCH 2/2] drm/bridge: ti-sn65dsi83: Fix problem with premature PLL locking

[Alexander Stein]

Hi,

Am Mittwoch, 15. Juli 2026, 16:14:42 CEST schrieb Frieder Schrempf:
> On 15.07.26 15:52, Gary Bisson wrote:
> > Hi Esben and Luca,
> > 
> > On Wed, Jul 15, 2026 at 10:52:18AM +0200, Luca Ceresoli wrote:
> >> On Sat, 11 Jul 2026 13:51:15 +0200, Esben Haabendal <esben@xxxxxxxxxx> wrote:
> >>
> >> Hi Esben,
> >>
> >> +Cc Gary
> >>
> >>> [...]
> >>>
> >>> This is the same issue as addressed in the patch by Gary Bisson [1],
> >>> but changing the ti-sn65dsi83 driver instead, so we don't have to change
> >>> all other drivers that could potentially be used with this chip.
> >>>
> >>> [1] https://lore.kernel.org/all/20260120-mtkdsi-v1-1-b0f4094f3ac3@xxxxxxxxx/
> >>
> >> AFAICU your patch would replace Gary's one. Also Gary's patch has been
> >> reported to introduce regressions but it hasn't been reverted yet. Can you
> >> reply to that thread mentioning your patch, so everybody in the discussion
> >> is aware of your alternative proposal?
> > 
> > Thanks for including me. I just tested this change and reverted my other
> > one (mtk_dsi) and confirm that it works on my Tungsten510 + SN65DSI83 +
> > tm070jdhg30 panel.
> > 
> > Tested-by: Gary Bisson <bisson.gary@xxxxxxxxx>
> > 
> > Note that the sn65dsi83 driver wasn't changed as I thought the PLL lock
> > in pre-enable was on purpose. It was introduced by Frieder with this
> > commit. Adding him to the thread to weigh in.
> > dd9e329af723 drm/bridge: ti-sn65dsi83: Fix enable/disable flow to meet spec
> 
> Thanks for the mention. This was introduced to keep the init order
> according to the datasheet. The DSI host first needs to put the DSI
> lanes into the correct state in its pre_enable(). Then the bridge needs
> to be enabled (including the PLL) in the pre_enable() of the bridge
> driver. Only after that the DSI host is allowed to stream data.
> 
> Moving the PLL init from pre_enable() to enable() probably violates this
> order. In the past this lead to sporadic issues with some hardware
> setups (depending on the display and the DSI host). Some of this is also
> described in the docs: [1]
> 
> So from the first glance, I would assume this issue needs to be fixed in
> the DSI host driver.
> 
> [1]
> https://docs.kernel.org/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation

This link says
> Ordinarily the downstream bridge DSI peripheral pre_enable will have been
> called before the DSI host. If the DSI peripheral requires LP-11 and/or the
> clock lane to be in HS mode prior to pre_enable, then it can set the
> pre_enable_prev_first flag to request the pre_enable (and post_disable)
> order to be altered to enable the DSI host first.

So IIRC if pre_enable() already requires LP-11 on data and HS on clock,
pre_enable_prev_first should be true then.

Best regards,
Alexander
-- 
TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
Amtsgericht München, HRB 105018
Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
http://www.tq-group.com/