On Mon, 2022-08-08 at 10:02 +0000, Lin, Wayne wrote: > [Public] > > > > > -----Original Message----- > > From: Lyude Paul <lyude@xxxxxxxxxx> > > Sent: Thursday, August 4, 2022 4:28 AM > > To: Lin, Wayne <Wayne.Lin@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx; > > nouveau@xxxxxxxxxxxxxxxxxxxxx; amd-gfx@xxxxxxxxxxxxxxxxxxxxx > > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>; Zuo, Jerry > > <Jerry.Zuo@xxxxxxx>; Jani Nikula <jani.nikula@xxxxxxxxx>; Imre Deak > > <imre.deak@xxxxxxxxx>; Daniel Vetter <daniel.vetter@xxxxxxxx>; Sean Paul > > <sean@xxxxxxxxxx>; Wentland, Harry <Harry.Wentland@xxxxxxx>; Li, Sun > > peng (Leo) <Sunpeng.Li@xxxxxxx>; Siqueira, Rodrigo > > <Rodrigo.Siqueira@xxxxxxx>; Deucher, Alexander > > <Alexander.Deucher@xxxxxxx>; Koenig, Christian > > <Christian.Koenig@xxxxxxx>; Pan, Xinhui <Xinhui.Pan@xxxxxxx>; David > > Airlie <airlied@xxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx>; Jani Nikula > > <jani.nikula@xxxxxxxxxxxxxxx>; Joonas Lahtinen > > <joonas.lahtinen@xxxxxxxxxxxxxxx>; Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>; > > Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>; Ben Skeggs > > <bskeggs@xxxxxxxxxx>; Karol Herbst <kherbst@xxxxxxxxxx>; Kazlauskas, > > Nicholas <Nicholas.Kazlauskas@xxxxxxx>; Li, Roman > > <Roman.Li@xxxxxxx>; Shih, Jude <Jude.Shih@xxxxxxx>; Simon Ser > > <contact@xxxxxxxxxxx>; Lakha, Bhawanpreet > > <Bhawanpreet.Lakha@xxxxxxx>; Mikita Lipski <mikita.lipski@xxxxxxx>; > > Claudio Suarez <cssk@xxxxxxxx>; Chen, Ian <Ian.Chen@xxxxxxx>; Colin Ian > > King <colin.king@xxxxxxxxx>; Wu, Hersen <hersenxs.wu@xxxxxxx>; Liu, > > Wenjing <Wenjing.Liu@xxxxxxx>; Lei, Jun <Jun.Lei@xxxxxxx>; Strauss, > > Michael <Michael.Strauss@xxxxxxx>; Ma, Leo <Hanghong.Ma@xxxxxxx>; > > Thomas Zimmermann <tzimmermann@xxxxxxx>; José Roberto de Souza > > <jose.souza@xxxxxxxxx>; He Ying <heying24@xxxxxxxxxx>; Anshuman > > Gupta <anshuman.gupta@xxxxxxxxx>; Andi Shyti > > <andi.shyti@xxxxxxxxxxxxxxx>; Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx>; > > Juston Li <juston.li@xxxxxxxxx>; Sean Paul <seanpaul@xxxxxxxxxxxx>; > > Fernando Ramos <greenfoo@xxxxxx>; Luo Jiaxing > > <luojiaxing@xxxxxxxxxx>; Javier Martinez Canillas <javierm@xxxxxxxxxx>; > > open list <linux-kernel@xxxxxxxxxxxxxxx>; open list:INTEL DRM DRIVERS > > <intel-gfx@xxxxxxxxxxxxxxxxxxxxx> > > Subject: Re: [RESEND RFC 18/18] drm/display/dp_mst: Move all payload info > > into the atomic state > > > > On Tue, 2022-07-05 at 09:10 +0000, Lin, Wayne wrote: > > > > +struct drm_dp_mst_port; > > > > + > > > > /* DP MST stream allocation (payload bandwidth number) */ > > > > struct dc_dp_mst_stream_allocation { > > > > uint8_t vcp_id; > > > > /* number of slots required for the DP stream in > > > > * transport packet */ > > > > uint8_t slot_count; > > > > + /* The MST port this is on, this is used to associate DC MST > > > > + payloads > > > > with their > > > > + * respective DRM payloads allocations, and can be ignored on non- > > > > Linux. > > > > + */ > > > > > > Is it necessary for adding this new member? Since this is for setting > > > the DC HW and not relating to drm. > > > > I don't entirely know, honestly. The reasons I did it: > > > > * Mapping things from DRM to DC and from DC to DRM is really confusing for > > outside contributors like myself, so it wasn't even really clear to me if > > there was another way to reconstruct the DRM context from the spots > > where > > we call from DC up to DM (not a typo, see next point). > > * These DC structs for MST are already layer mixing as far as I can tell, > > just not in an immediately obvious way. While this struct itself is for DC, > > there's multiple spots where we pass the DC payload structs down from > > DM to > > DC, then pass them back up from DC to DM and have to figure out how to > > reconstruct the DRM context that we actually need to use the MST helpers > > from that. So, that kind of further complicates the confusion of where > > layers should be separated. > > * As far as I'm aware with C there shouldn't be any issue with adding a > > pointer to a struct whose contents are undefined. IMHO, this is also > > preferable to just using void* because then at least you get some hint as > > to the actual type of the data and avoid the possibility of casting it to > > the wrong type. So tl;dr, on any platform even outside of Linux with a > > reasonably compliant compiler this should still build just fine. It'll even > > give you the added bonus of warning people if they try to access the > > contents of this member in DC on non-Linux platforms. If void* is preferred > > though I'm fine with switching it to that. > > > > -- > > Cheers, Lyude Paul (she/her) Software Engineer at Red Hat > > Hi Lyude, > > Thanks for your time! > I was thinking that our DC just mainly takes care of HW related programming. > Struct dc_dp_mst_stream_allocation is only used to construct a copy of the virtual > channel payload ID and slots count of payload allocation table determined by > dm/drm. ID and slots are only things required for programming HW registers. > I think there shouldn't be any spots to try to construct the DRM context from > this dc struct since there is no such concept in HW level. Our HW should only > take care of local DP link and it doesn't have overall topology info. Looking at the code I wrote again and realizing I slightly misspoke, looking at the code again I think I probably can drop this. It's likely I just got totally lost with the DC codebase and thought this was necessary when it wasn't. Will drop in the respin > > Thanks! > > Regards, > Wayne -- Cheers, Lyude Paul (she/her) Software Engineer at Red Hat