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

[Yegor Yefremov <yegorslists@googlemail.com>]

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:
> > >
> > > * Tony Lindgren <tony@atomide.com> [190927 15:20]:
> > > > * Yegor Yefremov <yegorslists@googlemail.com> [190927 12:31]:
> > > > > On Fri, Sep 27, 2019 at 10:18 AM Yegor Yefremov
> > > > > <yegorslists@googlemail.com> wrote:
> > > > > >
> > > > > > I was porting my system from 3.18/4.2 to 5.3. During this process I
> > > > > > noticed that FT4232 that is attached directly to musb is not working
> > > > > > correctly when opened for the first time: tx is working but nothing
> > > > > > can be received. On the second opening everything is working fine.
> > > > > > When the same chip is connected via a USB hub - everything is working
> > > > > > from the very beginning.
> > > > > >
> > > > > > I could reproduce this issue using BeagleBone Black with omap2plus_defconfig.
> > > > > >
> > > > > > # lsusb -t
> > > > > > +/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=musb-hdrc/1p, 480M
> > > > > >     |__ Port 1: Dev 2, If 0, Class=, Driver=ftdi_sio, 480M
> > > > > >     |__ Port 1: Dev 2, If 1, Class=, Driver=ftdi_sio, 480M
> > > > > >     |__ Port 1: Dev 2, If 2, Class=, Driver=ftdi_sio, 480M
> > > > > >     |__ Port 1: Dev 2, If 3, Class=, Driver=ftdi_sio, 480M
> > > > > >
> > > > > > git bisect revealed the following:
> > > > > >
> > > > > > fdea2d09b997ba4c86e7a707a5fac87c305f2131 is the first bad commit
> > > > > > commit fdea2d09b997ba4c86e7a707a5fac87c305f2131
> > > > > > Author: Tony Lindgren <tony@atomide.com>
> > > > > > Date:   Wed Aug 31 07:19:59 2016 -0700
> > > > > >
> > > > > >     dmaengine: cppi41: Add basic PM runtime support
> > > > > >
> > > > > >     Let's keep the device enabled between cppi41_dma_issue_pending()
> > > > > >     and dmaengine_desc_get_callback_invoke() and rely on the PM runtime
> > > > > >     autoidle timeout elsewhere.
> > > > > >
> > > > > >     As the PM runtime is for whole device, not for each channel,
> > > > > >     we need to queue pending transfers if the device is PM runtime
> > > > > >     suspended. Then we start the pending transfers in PM runtime
> > > > > >     resume.
> > > > > >
> > > > > >     Signed-off-by: Tony Lindgren <tony@atomide.com>
> > > > > >     Signed-off-by: Vinod Koul <vinod.koul@intel.com>
> > > > > >
> > > > > > :040000 040000 8cf92c09083541dfdee01cc2973e73ef520f4fb1
> > > > > > a03c1a7ba8e723f7b503733c46edaa4141483265 M      drivers
> > > > > >
> > > > > > Any idea?
> > > > >
> > > > > The problems can be reproduced with other FTDI chips like FT232R.
> > > > >
> > > > > Invoking "minicom -D /dev/ttyUSB0" and typing some characters is
> > > > > enough to reproduce the issue (just in case, hw flow control should be
> > > > > disabled).
> > > > >
> > > > > cp210x based converter is working without an issue. So only FTDI chips
> > > > > are affected so far.
> > > >
> > > > Hmm OK. Maybe this could be an issue where the FTDI chip takes
> > > > longer to enumerate and cppi41 is already suspended by then?
> > > >
> > > > At least we had a similar issue with commit ae4a3e028bb8
> > > > ("dmaengine: cppi41: Fix runtime PM timeouts with USB mass
> > > > storage").
> > >
> > > 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.

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),
          },
  };

Yegor