Re: musb: cppi41: broken high speed FTDI functionality when connected to musb directly

[Sebastian Reichel <sre@kernel.org>]

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Hi,

On Mon, Sep 30, 2019 at 08:23:30AM -0700, Tony Lindgren wrote:
> * Tony Lindgren <tony@atomide.com> [190930 14:57]:
> > * Yegor Yefremov <yegorslists@googlemail.com> [190930 08:20]:
> > > On Mon, Sep 30, 2019 at 8:59 AM Yegor Yefremov
> > > <yegorslists@googlemail.com> wrote:
> > > >
> > > > On Sat, Sep 28, 2019 at 6:09 PM Yegor Yefremov
> > > > <yegorslists@googlemail.com> wrote:
> > > > >
> > > > > On Fri, Sep 27, 2019 at 5:57 PM Tony Lindgren <tony@atomide.com> wrote:
> > > > > > Looks like I'm unable to reproduce this with bbb and FT232R
> > > > > > USB UART.
> > > > > >
> > > > > > I tried v5.3 with omap2plus_defconfig, then boot, load musb
> > > > > > and ftdi-sio modules, then connect ftdi directly to bbb,
> > > > > > and then run "minicom -D /dev/ttyUSB0" on bbb and it works
> > > > > > just fine for me.
> > > > > >
> > > > > > I tried also rebooting the device inbetween in case it only
> > > > > > happens on the first connect after boot but still no luck
> > > > > > reproducing.
> > > > >
> > > > > Strange. I've used a loopback to check whether the characters will be echoed.
> > > > > FTDI cable was connected all the time so that I could check RX right after boot.
> > > > > Both Buildroot and OpenWrt rootfs's showed this behaviour.
> > > > >
> > > > > > Maybe try adding some debug prints to cppi41_runtime_suspend()
> > > > > > and cppi41_runtime_resume() to see if gets runtime suspended
> > > > > > too early?
> > > > >
> > > > > Will do on Mo.
> > > >
> > > > I've added the printks to both routines and the result is quite
> > > > interesting. On the system with a directly attached FTDI both routines
> > > > will be always invoked before (resume) and after (suspend) the
> > > > test/minicom i.e. during the USB initialization.
> > > >
> > > > On the systems with a USB hub, these routines will be invoked only
> > > > during the USB initialization and the last invocation is resume.
> > > > During the test, there are no invocations.
> > 
> > Hmm OK thanks. Hard to say still based on that what might be missing.
> > 
> > I just tried also musb and phy built-in with FTDI connected on
> > boot, but still no luck reproducing the issue here.
> > 
> > > Removing PM routines workarounds the issue. Quick and dirty.
> > > 
> > >  static struct platform_driver cpp41_dma_driver = {
> > >           .probe  = cppi41_dma_probe,
> > >           .remove = cppi41_dma_remove,
> > >           .driver = {
> > >                   .name = "cppi41-dma-engine",
> > >                   /*.pm = &cppi41_pm_ops,*/
> > >                   .of_match_table = of_match_ptr(cppi41_dma_ids),
> > >           },
> > >   };
> > 
> > Well doing something like this to disable autosuspend might
> > be less intrusive until this one is fixed:
> > 
> > # echo on > /sys/bus/platform/drivers/musb-hdrc/musb-hdrc.1/power/control
> > 
> > But before that, maybe try with control set to auto, and increase the
> > autosuspend_delay_ms from 500 ms to let's say 2500 ms:
> > 
> > # echo 2500 > /sys/bus/platform/drivers/musb-hdrc/musb-hdrc.1/power/autosuspend_delay_ms
> > 
> > That is assuming the musb instance is 1 on your board, replace
> > with musb-hdrc.0 if a different interface from bbb.
> 
> Actually playing with the cppi41 timeout might be more suitable here,
> they use the same module clock from what I remember though. So
> maybe increase the cppi41 autosuspend_timeout from 100 ms to 500 ms
> or higher:
> 
> # echo 500 > /sys/bus/platform/drivers/cppi41-dma-engine/47400000.dma-controller/power/autosuspend_delay_ms
> 
> If changing the autosuspend_timeout_ms value does not help, then
> try setting control to on there.

I did not check the details, but from the cover-letter this might be
woth looking into:

https://lore.kernel.org/lkml/20190930161205.18803-1-johan@kernel.org/

-- Sebastian

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