On Mi, 2026-07-29 at 13:54 +0530, Yashas D wrote: > > > On 29/07/26 04:07, Dominik Haller wrote: > > On Di, 2026-07-28 at 18: 23 +0530, Yashas D wrote: > This series > > adds > > 'no-hpd' device tree property support to the Cadence > MHDP8546 > > bridge > > driver for boards where the HPD line cannot be used > for > hotplug > > detection. > > > > > > > > On Di, 2026-07-28 at 18:23 +0530, Yashas D wrote: > > > This series adds 'no-hpd' device tree property support to the > > > Cadence > > > MHDP8546 bridge driver for boards where the HPD line cannot be > > > used > > > for > > > hotplug detection. > > > > > > On TI J721S2 EVMs, the HPD signal is routed to SoC pin AA24 > > > (MCASP1_ACLKX/DP0_HPD). This pin is muxed with the McASP1 audio > > > bit > > > clock; selecting DP0_HPD breaks audio. There is no alternative > > > pin > > > carrying the HPD signal which makes it impossible to use HPD > > > without loosing the audio capabilities. > > Hi Yashas, > > > > this description is not correct. On the J721S2 EVM the pin AA24 > > MCASP1_ACLKX is not used for audio. > > The pin is just floating unless this "GESI"-board with an > > additional > > ethernet interface is connect. AA24 is used as as > > MCASP1_ACLKX.RGMII1_RD0 in this case. > > See arch/arm64/boot/dts/ti/k3-j721s2-evm-gesi-exp-board.dtso > > > > Also the AA24 pin needs to be configured as HPD pin (muxmode 3) > > otherwise the mhdp firmware will not turn on the bridge. > > > > Dominik > > > > > > Hi Dominik, > > You are correct, I apologise for the error. The SoC PAD mux conflict > on AA24 is with RGMII1_RD0 (GESI ethernet expansion board), not > MCASP1 > audio. I will fix the commit message. > > The full picture on J721S2X-PM1-SOM rev E2: > > - The HPD resistor is DNI from factory, so AA24 is not physically > connected to the DP connector HPD line by default. However AA24 > must > still be configured in DP0_HPD mux mode (mode 3) for the MHDP > firmware > to operate at all — configuring it in any other mode prevents the > bridge from loading. > > - When we physically connected HPD by populating the resistor, the E2 > board failed to boot with a monitor attached. The HPD line leaks > voltage > from the monitor into the SoC while powered off, causing a PMIC > error. > This was fixed in rev E3+ with an HPD buffer. Our boards are rev > E2. > > The audio conflict in earlier message versions was our mistake. It > came from investigating whether an alternative routing path through a > board-level signal MUX chip (MUX1/MUX2) on the SOM could expose a > GPIO > for HPD — changing that MUX's port selection would have affected > audio. > That is unrelated to the SoC PAD mux and should not have been > mentioned. > > I will fix the message and send a new version. Hi Yashas,
please also update the commit description of the actual patch 2/2 as it implies at the moment that you can use the AA24 pin for other functions while using the display port. Thanks Dominik > > Thanks, > Yashas D > > > > When 'no-hpd' is set, DRM_BRIDGE_OP_HPD is omitted so the > > > framework > > > falls back to polling .detect() every ~10 seconds. Monitor > > > presence > > > is > > > determined via AUX DPCD reads instead of firmware HPD status > > > registers. > > > The .detect() callback drives cdns_mhdp_update_link_status() on > > > each > > > poll to keep mhdp->plugged current. At attach time, the driver > > > waits > > > for firmware to be ready before performing the initial AUX poll > > > since > > > no interrupt will trigger it. > > > > > > Changes since v4: > > > - Corrected the dt-binding Subject > > > > > > Link to v4: > > > https://urldefense.com/v3/__https://lore.kernel.org/ > > > > > all/[email protected]/__;!!G3vK! > > XKetSJhTJzSznMTBeoww63bvXSPD3xrWstRrf4H6AhnrM5IjIvNFa9uHVVWEYPEoe0G > > NrZXGb8IF$ > > <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2F > > urldefense.com%2Fv3%2F__https%3A%2F%2Flore.kernel.org%2Fall%2F20260 > > 630102610.1849902-1-y- > > d%40ti.com%2F__%3B!!G3vK!XKetSJhTJzSznMTBeoww63bvXSPD3xrWstRrf4H6Ah > > nrM5IjIvNFa9uHVVWEYPEoe0GNrZXGb8IF%24&data=05%7C02%7Cd.haller%40phy > > tec.de%7Ce1e53182268a4df81d1908deed4ada4b%7Ce609157c80e2446d9be39c9 > > 9c2399d29%7C0%7C0%7C639209102909756678%7CUnknown%7CTWFpbGZsb3d8eyJF > > bXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWF > > pbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=2TH3dx%2FirnEKUcHFu9vOz%2F > > ZT9JSyfcyMp%2BDjQPDUC%2F0%3D&reserved=0> > > > > > > Rahul T R (2): > > > dt-bindings: display: bridge: cdns,mhdp8546: Add no-hpd > > > property to > > > the cadence bridge > > > drm: bridge: cdns-mhdp8546: Add no-hpd property > > > > > > .../display/bridge/cdns,mhdp8546.yaml | 17 ++++++ > > > .../drm/bridge/cadence/cdns-mhdp8546-core.c | 58 > > > ++++++++++++++++- > > > -- > > > .../drm/bridge/cadence/cdns-mhdp8546-core.h | 1 + > > > 3 files changed, 69 insertions(+), 7 deletions(-) > > > > > >
