On 2025-02-12 08:16:41, James A. MacInnes wrote: > On Wed, 12 Feb 2025 11:03:39 +0100 > Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx> wrote: > > > On 2025-02-11 19:42:24, James A. MacInnes wrote: > > > SDM845 DPU hardware is rev 4.0.0 per hardware document. > > > > Just checking: version 4.0.0 is not named in the code that you're > > changing: are you mentioning this because the patch you're fixing > > here [1] says that widebus is "recommended" on 5.x.x which includes > > sc7180, yet didn't account for that sc7180_dp_descs also being used > > in the SDM845 compatible which is 4.0.0? That is something worth > > mentioning in the patch description. > > > > [1]: > > https://lore.kernel.org/linux-arm-msm/20240730195012.2595980-1-quic_abhinavk@xxxxxxxxxxx/ > > That is correct. All the 'modern' Qualcomm dpus got wide-bus turned on > and as the SDM845 has not had a working Type-C port it was never tested. > > Happy to add that to my commit message. This is my second submission to > the kernel forum. Thanks, would be great to include all of this as context in some form! > > > Incorrect setting caused inop displayport. > > > > Inop doesn't seem to be a common abbreviation, there's enough space > > to spell out "inoperative". And spend some more words on _why_ this > > is an "incorrect setting" in the first place (based on the > > suggestion above)? > > > > Happy to spend many more words. Just looking to meet the requirements > for the boards and try to not ruffle any feathers. It seems to easy to > be far too verbose. I'd say: the more the merrier. Especially DRM/MSM is *flooded* with poorly-worded series, if they include a description (beyond paraphrasing the title...) at all :(. Having all this context available makes it possible to understand the debugging and thought process behind a change. Links to downstream are a great way to showcase how things are dealt with there, as it's generally the only source of "documentation" for these drivers (to hobbyist contributors like myself). > > > I am trying to remember the details from the original widebus series: > > we discussed that the INTF_CFG2_DATABUS_WIDEN flag was available > > starting with DPU 4.0.0 (IIRC, cannot find the source), yet the DSI > > host only supports it from 6G v2.5 onwards (SC7280 and up?) [2]. > > Seems a similar limitation applies to DP hosts. > > > > [2]: > > https://lore.kernel.org/linux-arm-msm/20230822-add-widebus-support-v4-4-9dc86083d6ea@xxxxxxxxxxx/ > > > > That would reflect the testing I have performed. With the wide_bus > system enabled, The MIPI display functions fine, but the Altmode > DisplayPort (type-c to DP) does not turn on a standard monitor and the > type-c to HDMI connection has either a system that does not sync > (horrific flashing) or just a single solid line. At other resolutions I > was getting vblank errors from deeper into the system. Technically the MIPI DSI display (data connection between DPU INTF and DSI host AFAIR) shouldn't be using wide_bus, AFAIK it has DSI host 6G v2.4 which doesn't support it according to the code. Thanks for taking all these suggestions! - Marijn
