On 2023-04-14 10:57:45, Abhinav Kumar wrote: > On 4/14/2023 10:34 AM, Marijn Suijten wrote: > > On 2023-04-14 08:48:43, Abhinav Kumar wrote: > >> On 4/14/2023 12:35 AM, Marijn Suijten wrote: > >>> On 2023-04-12 10:33:15, Abhinav Kumar wrote: > >>> [..] > >>>>> What happens if a device boots without DSC panel connected? Will > >>>>> CTL_DSC_FLUSH be zero and not (unnecessarily, I assume) flush any of the > >>>>> DSC blocks? Or could this flush uninitialized state to the block? > >>>> > >>>> If we bootup without DSC panel connected, the kernel's cfg->dsc will be > >>>> 0 and default register value of CTL_DSC_FLUSH will be 0 so it wont flush > >>>> any DSC blocks. > >>> > >>> Ack, that makes sense. However, if I connect a DSC panel, then > >>> disconnect it (now the register should be non-zero, but cfg->dsc will be > >>> zero), and then replug a non-DSC panel multiple times, it'll get flushed > >>> every time because we never clear CTL_DSC_FLUSH after that? > >> > >> If we remove it after kernel starts, that issue is there even today > >> without that change because DSI is not a hot-pluggable display so a > >> teardown wont happen when you plug out the panel. How will cfg->dsc be 0 > >> then? In that case, its not a valid test as there was no indication to > >> DRM that display was disconnected so we cannot tear it down. > > > > The patch description itself describes hot-pluggable displays, which I > > believe is the upcoming DSC support for DP? You ask how cfg->dsc can > > become zero, but this is **exactly** what the patch description > > describes, and what this patch is removing the `if` for. If we are not > > allowed to discuss that scenario because it is not currently supported, > > neither should we allow to apply this patch. > > > > With that in mind, can you re-answer the question? > > I didnt follow what needs to be re-answered. > > This patch is being sent in preparation of the DSC over DP support. This > does not handle non-hotpluggable displays. Good, because my question is specifically about *hotpluggable* displays/panels like the upcoming DSC support for DP. After all there would be no point in me suggesting to connect and disconnect non-hotpluggable displays and expect something sensible to happen, wouldn't it? Allow me to copy-paste the question again for convenience, with some minor wording changes: However, if I connect a DSC DP display, then disconnect it (now the register should be non-zero, but cfg->dsc will be zero), and then connect and reconnect a non-DSC DP display multiple times, it'll get flushed every time because we never clear CTL_DSC_FLUSH after that? And the missing part is: would multiple flushes be harmful in this case? > I do not think dynamic switch > between DSC and non-DSC of non-hotpluggable displays needs to be > discussed here as its not handled at all with or without this patch. > > We wanted to get early reviews on the patch. If you want this patch to > be absorbed when rest of DSC over DP lands, I have no concerns with > that. I wont pick this up for fixes and we will land this together with > the rest of DP over DSC. I don't mind when and where this lands, just want to have the semantics clear around persisting the value of CTL_DSC_FLUSh in the register. Regardless, this patch doesn't sound like a fix but a workaround until reset_intf_cfg() is fixed to be called at the right point, and extended to clear CTL_DSC_ACTIVE and flush the DSCs. Perhaps it shouldn't have a Fixes: tag for that reason, as you intend to reinstate this if (cfg->dsc) condition when that is done? - Marijn
