Hi Lucas On Fri, 10 Jun 2022 at 08:52, Lucas Stach <l.stach@xxxxxxxxxxxxxx> wrote: > > Hi, > > Am Mittwoch, dem 11.05.2022 um 16:58 +0200 schrieb Marek Szyprowski: > > Hi Dave, > > > > On 05.04.2022 13:43, Dave Stevenson wrote: > > > On Fri, 18 Mar 2022 at 12:25, Dave Stevenson > > > <dave.stevenson@xxxxxxxxxxxxxxx> wrote: > > > > On Fri, 4 Mar 2022 at 15:18, Dave Stevenson > > > > <dave.stevenson@xxxxxxxxxxxxxxx> wrote: > > > > > Hi All > > > > A gentle ping on this series. Any comments on the approach? > > > > Thanks. > > > I realise the merge window has just closed and therefore folks have > > > been busy, but no responses on this after a month? > > > > > > Do I give up and submit a patch to document that DSI is broken and no one cares? > > > > Thanks for pointing this patchset in the 'drm: bridge: Add Samsung MIPI > > DSIM bridge' thread, otherwise I would miss it since I'm not involved > > much in the DRM development. > > > > This resolves most of the issues in the Exynos DSI and its recent > > conversion to the drm bridge framework. I've added the needed > > prepare_upstream_first flags to the panels and everything works fine > > without the bridge chain order hacks. > > > > Feel free to add: > > > > Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > > > > > > The only remaining thing to resolve is the moment of enabling DSI host. > > The proper sequence is: > > > > 1. host power on, 2. device power on, 3. host init, 4. device init, 5. > > video enable. > > > > #1 is done in dsi's pre_enable, #2 is done in panel's prepare. #3 was so > > far done in the first host transfer call, which usually happens in > > panel's prepare, then the #4 happens. Then video enable is done in the > > enable callbacks. > > > > Jagan wants to move it to the dsi host pre_enable() to let it work with > > DSI bridges controlled over different interfaces > > (https://lore.kernel.org/all/20220504114021.33265-6-jagan@xxxxxxxxxxxxxxxxxxxx/ > > ). This however fails on Exynos with DSI panels, because when dsi's > > pre_enable is called, the dsi device is not yet powered. I've discussed > > this with Andrzej Hajda and we came to the conclusion that this can be > > resolved by adding the init() callback to the struct mipi_dsi_host_ops. > > Then DSI client (next bridge or panel) would call it after powering self > > on, but before sending any DSI commands in its pre_enable/prepare functions. > > > > I've prepared a prototype of such solution. This approach finally > > resolved all the initialization issues! The bridge chain finally matches > > the hardware, no hack are needed, and everything is controlled by the > > DRM core. This prototype also includes the Jagan's patches, which add > > IMX support to Samsung DSIM. If one is interested, here is my git repo > > with all the PoC patches: > > > > https://github.com/mszyprow/linux/tree/v5.18-next-20220511-dsi-rework > > While this needs rework on the bridge chip side, I fear that we need > something like that to allow the bridge to control the sequencing of > the DSI host init. While most bridges that aren't controlled via the > DSI channel might be fine with just initializing the host right before > a video signal is driven, there are some that need a different > sequencing. > > The chip I'm currently looking at is a TC368767, where the datasheet > states that the DSI lanes must be in LP-11 before the reset is > released. While the datasheet doesn't specify what happens if that > sequence is violated, Marek Vasut found that the chip enters a test > mode if the lanes are not in LP-11 at that point and I can confirm this > observation. > Now with the TC358767 being a DSI to (e)DP converter, we need to > release the chip from reset pretty early to establish the DP AUX > connection to communicate with the display, in order to find out which > video modes we can drive. As the chip is controlled via i2c in my case, > initializing the DSI host on first DSI command transaction is out and > doing so before the bridge pre_enable is way too late. > > What I would need for this chip to work properly is an explicit call, > like the mipi_dsi_host_init() added in the PoC above, to allow the > bridge driver to kick the DSI host initialization before releasing the > chip from reset state. This is going off on a slight tangent from the original patch set, but a thought has just come to mind for this use case. For this sort of bridge device where you want to power up early (either just for LP-11 state, or for HS on the clock lane), is power up at mipi_dsi_attach, and power down at mipi_dsi_detach sufficient? We have mode_flags in struct mipi_dsi_device passed in mipi_dsi_attach, so an extra flag in there (eg MIPI_DSI_EARLY_POWER_ON) would be very easy and be a simple way to signal an alternate DSI host behaviour. It still leaves the configuration of link frequency as an open question, but potentially solves the sequencing issue. Just a thought. Perhaps dsi_attach() is still too late in the process. Dave
