On Tue, 16 Jul 2024 at 18:58, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: > > Hi > > Am 27.02.24 um 23:40 schrieb Dmitry Baryshkov: > > Hello, > > > > We are currently looking at checking and/or possibly redesigning the > > way the MSM DRM driver handles the HPD events and link training. > > > > After a quick glance at the drivers implementing DP support, I noticed > > following main approaches: > > - Perform link training at the atomic_enable time, don't report > > failures (mtk, analogix, zynqmp, tegra, nouveau) > > - Perform link training at the atomic_enable time, report errors using > > link_status property (i915, mhdp8546) > > - Perform link training on the plug event (msm, it8605). > > - Perform link training from the DPMS handler, also calling it from > > the enable callback (AMDGPU, radeon). > > > > It looks like the majority wins and we should move HPD to > > atomic_enable time. Is that assumption correct? > > Did you ever receive an answer to this question? I currently investigate > ast's DP code, which does link training as part of detecting the > connector state (in detect_ctx). But most other drivers do this in > atomic_enable. I wonder if ast should follow. Short answer: yes, the only proper place to do it is atomic_enable(). Long answer: I don't see a way to retrigger link training in ast_dp.c Without such change you are just shifting things around. The end-result of moving link-training to atomic_enable() is that each enable can trigger link training, possibly lowering the link rate, etc. if link training is just a status bit from the firmware that we don't control, it doesn't make real-real sense to move it. > > Best regards > Thomas > > > > > Also two related questions: > > - Is there a plan to actually make use of the link_status property? > > Intel presented it at FOSDEM 2018, but since that time it was not > > picked up by other drivers. > > > > - Is there any plan to create generic DP link training helpers? After > > glancing through the DP drivers there is a lot of similar code in the > > link training functions, with minor differences here and there. And > > it's those minor differences that bug me. It means that drivers might > > respond differently to similar devices. Or that there might be minor > > bugs here and there. > > > > -- > -- > Thomas Zimmermann > Graphics Driver Developer > SUSE Software Solutions Germany GmbH > Frankenstrasse 146, 90461 Nuernberg, Germany > GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman > HRB 36809 (AG Nuernberg) > -- With best wishes Dmitry
