On Mon, 23 Oct 2023 at 09:52, Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx> wrote: > > Hi Dmitry, > > Am Sonntag, 22. Oktober 2023, 12:49:41 CEST schrieb Dmitry Baryshkov: > > On Thu, 19 Oct 2023 at 14:42, Alexander Stein > > > > <alexander.stein@xxxxxxxxxxxxxxx> wrote: > > > Hi, > > > > > > Am Donnerstag, 19. Oktober 2023, 13:19:51 CEST schrieb Dmitry Baryshkov: > > > > On Thu, 19 Oct 2023 at 12:26, Maxime Ripard <mripard@xxxxxxxxxx> wrote: > > > > > On Mon, Oct 16, 2023 at 07:53:48PM +0300, Dmitry Baryshkov wrote: > > > > > > The MIPI DSI links do not fully fall into the DRM callbacks model. > > > > > > > > > > Explaining why would help > > > > > > > > A kind of explanation comes afterwards, but probably I should change > > > > the order of the phrases and expand it: > > > > > > > > The atomic_pre_enable / atomic_enable and correspondingly > > > > atomic_disable / atomic_post_disable expect that the bridge links > > > > follow a simple paradigm: either it is off, or it is on and streaming > > > > video. Thus, it is fine to just enable the link at the enable time, > > > > doing some preparations during the pre_enable. > > > > > > > > But then it causes several issues with DSI. First, some of the DSI > > > > bridges and most of the DSI panels would like to send commands over > > > > the DSI link to setup the device. Next, some of the DSI hosts have > > > > limitations on sending the commands. The proverbial sunxi DSI host can > > > > not send DSI commands after the video stream has started. Thus most of > > > > the panels have opted to send all DSI commands from pre_enable (or > > > > prepare) callback (before the video stream has started). > > > > > > > > However this leaves no good place for the DSI host to power up the DSI > > > > link. By default the host's pre_enable callback is called after the > > > > DSI bridge's pre_enable. For quite some time we were powering up the > > > > DSI link from mode_set. This doesn't look fully correct. And also we > > > > got into the issue with ps8640 bridge, which requires for the DSI link > > > > to be quiet / unpowered at the bridge's reset time. > > > > > > There are also bridges (e.g. tc358767) which require DSI-LP11 upon bridge > > > reset. And additionally this DSI-(e)DP bridge requires LP11 while > > > accessing > > > DP-AUX channel, e.g. reading EDID. So bridges need at least some control > > > over DSI line state. > > > > For sending commands in LP11 it is typical to toggle the > > MIPI_DSI_MODE_LPM flag, for example see panel-=jdi-lt070me05000.c or > > some other drives. It might be a good idea to make that more explicit. > > All suggestions here would be appreciated. > > The biggest difference between that display and the tc358767 bridge is that > the display uses DSI commands, while the bridge is using i2c transfer to issue > DP-AUX commands. There is no host_transfer [1] which would enable LP-11. > It seems this DSI-DP bridge requires LP-11/HS on DSI lanes all times. This > contradicts current Linux behaviour. I see. I took a quick glance at the driver. Does the device mark AUX as busy when there is a HS transfer? Because otherwise it might be pretty hard to synchronise DP-AUX transfers with the DSI link state. We might need to add an API for this, if the DSI hosts actually can signal the blanking / DSI LP. Side note: the driver needs some care. It doesn't support the aux-bus bindings for eDP panels, it doesn't support other bridges on top of DP connectors (but there can be e..g. dp-connector device). > > Best regards, > Alexander > > [1] https://www.kernel.org/doc/html/latest/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation -- With best wishes Dmitry
