On Fri 20 Mar 09:30 PDT 2020, Evan Green wrote: > On Fri, Mar 20, 2020 at 3:22 AM Akash Asthana <akashast@xxxxxxxxxxxxxx> wrote: > > > > Hi Evan, Matthias, > > > > On 3/20/2020 1:13 AM, Matthias Kaehlcke wrote: > > > On Wed, Mar 18, 2020 at 02:24:35PM +0530, Akash Asthana wrote: > > >> Hi Matthias, > > >> > > >> On 3/17/2020 11:59 PM, Matthias Kaehlcke wrote: > > >>> Hi Akash, > > >>> > > >>> On Tue, Mar 17, 2020 at 04:27:47PM +0530, Akash Asthana wrote: > > >>>> Hi Matthias, > > >>>> > > >>>> On 3/14/2020 2:14 AM, Matthias Kaehlcke wrote: > > >>>>> Hi Akash, > > >>>>> > > >>>>> On Fri, Mar 13, 2020 at 06:42:09PM +0530, Akash Asthana wrote: > > >>>>>> V1 patch@https://patchwork.kernel.org/patch/11386469/ caused SC7180 system > > >>>>>> to reset at boot time. > > >>>>> The v1 patch isn't relevant in the commit message, please just describe the > > >>>>> problem. Also the crash only occurs when earlycon is used. > > >>>> ok > > >>>>>> As QUP core clock is shared among all the SE drivers present on particular > > >>>>>> QUP wrapper, the reset seen is due to earlycon usage after QUP core clock > > >>>>>> is put to 0 from other SE drivers before real console comes up. > > >>>>>> > > >>>>>> As earlycon can't vote for it's QUP core need, to fix this add ICC > > >>>>>> support to common/QUP wrapper driver and put vote for QUP core from > > >>>>>> probe on behalf of earlycon and remove vote during sys suspend. > > >>>>> Only removing the vote on suspend isn't ideal, the system might never get > > >>>>> suspended. That said I don't have a really good alternative suggestion. > > >>>>> > > >>>>> One thing you could possibly do is to launch a delayed work, check > > >>>>> console_device() every second or so and remove the vote when it returns > > >>>>> non-NULL. Not claiming this would be a great solution ... > > >>>>> > > >>>>> The cleanest solution might be a notifier when the early console is > > >>>>> unregistered, it seems somewhat over-engineered though ... Then again > > >>>>> other (future) uart drivers with interconnect support might run into > > >>>>> the same problem. > > >>>> We are hitting this problem because QUP core clocks are shared among all the > > >>>> SE driver present in particular QUP wrapper, if other HW controllers has > > >>>> similar architecture we will hit this issue. > > >>>> > > >>>> How about if we expose an API from common driver(geni-se) for putting QUP > > >>>> core BW vote to 0. > > >>>> > > >>>> We call this from console probe just after uart_add_one_port call (console > > >>>> resources are enabled as part of this call) to put core quota to 0 on behalf > > >>>> of earlyconsole? > > >>> From my notes from earlier debugging I have doubts this would work: > > >>> > > >>> There is a short window where the early console and the 'real' console coexist: > > >>> > > >>> [ 3.858122] printk: console [ttyMSM0] enabled > > >>> [ 3.875692] printk: bootconsole [qcom_geni0] disabled > > >>> > > >>> The reset probably occurs when the early console tries to write, but the ICC > > >>> is effectively disabled because ttyMSM0 and the other geni ports are runtime > > >>> suspended. > > >> Code flow from console driver probe(qcom_geni_serial.c) > > >> > > >> uart_add_one_port--->uart_configure_port--->{ 1) uart_change_pm(enable > > >> console resources) 2)register_console(boot to real console switch happens > > >> here)} > > >> > > >> Console resources are not disabled from anywhere before the switch happens > > >> completely. I meant to say until we saw below logs. > > >> > > >> [ 3.875692] printk: bootconsole [qcom_geni0] disabled > > >> > > >> I think the board reset issue cannot occur during the window where early > > >> console and 'real' console coexist. > > > Thanks for the clarification! Indeed my notes were only a hypothesis, I > > > don't see evidence that there is an actual downvote shortly after console > > > registration. > > > > > >> I have validated proposed solution by me, it is working fine. > > >> > > >> Currently voting is done for every QUP and not only to which earlycon is > > >> connect, with the above approach we can't remove vote from other QUPs. > > >> > > >> However we can limit voting only to earlycon QUP by removing interconnect > > >> from DT node of other QUPs. > > >> > > >> I am not sure how clean is this solution. > > > I'm more inclined towards a solution along the lines of what Evan > > > proposed, i.e. delaying the votes (either in geni or ICC) until we > > > are ready. > > > > Based on discussion I think the delayed solution is most suited if > > implemented in ICC core because other ICC client might face the similar > > problem. > > > > However for geni case I am more inclined towards below proposed solution. > > > > ----------------------------------------------------------------------------------------------------- > > > > How about if we expose an API from common driver(geni-se) for putting QUP > > core BW vote to 0. > > > > We call this from console probe just after uart_add_one_port call (console > > resources are enabled as part of this call) to put core quota to 0 on behalf > > of earlyconsole? > > This seems ok to me. Earlycon sets up a vote, and then real probe > tears it down. As long as in the shuffle of all of these things into > SE library helpers you still have a way of differentiating the > earlycon vote from the real vote. Note though that the boot console will outlive the real console when the kernel is booted with "keep_bootcon" on the command line (something I do from time to time). So rather than relying on "real probe" to signal when we can release the earlycon's icc vote I think we should specify dev->con->exit in qcom_geni_serial_earlycon_setup(), so that it will signal when the earlycon actually goes away - and until that point the clocks should just be on. > In other words, don't reuse this > early icc_path for the real UART vote. You should probably also > destroy the path once you've voted zero on it. Maintaining the early and real votes completely separate sounds like a sure way to keep this sane; and there's no drawback on having multiple votes for the same thing and rely on the framework to keep track of the various users. Regards, Bjorn
