Am 10.06.22 um 09:52 schrieb Lucas Stach: > 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. The SN65DSI84 also has this requirement according to the datasheet. > 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. So to sum up on the missing parts: 1. This series needs more reviews, but is generally agreed on. 2. Jagan will integrate Marek's mipi_dsi_host_init() PoC when respinning his series "drm: bridge: Add Samsung MIPI DSIM bridge". 3. Bridge drivers need to be adjusted to call mipi_dsi_host_init() if required. Did I get anything wrong here, or is there some point that I'm missing? Jagan, do you have any plan to pick up the threads? Thanks Frieder
