[PATCH v2 1/2] serial: ns16550: Revert "Move PCI access from ofdata_to_platdata() to probe()"

[Bin Meng]

Hi Simon,

On Mon, Apr 6, 2020 at 11:43 AM Simon Glass <sjg at chromium.org> wrote:
>
> Hi Bin,
>
> On Fri, 3 Apr 2020 at 02:35, Bin Meng <bmeng.cn at gmail.com> wrote:
> >
> > Hi Wolfgang,
> >
> > On Fri, Apr 3, 2020 at 4:26 PM Wolfgang Wallner
> > <wolfgang.wallner at br-automation.com> wrote:
> > >
> > >
> > > Hi Andy, Bin,
> > >
> > > > -----"Andy Shevchenko" <andy.shevchenko at gmail.com> schrieb: -----
> > > > On Thu, Apr 2, 2020 at 7:55 AM Bin Meng <bmeng.cn at gmail.com> wrote:
> > > > > On Thu, Apr 2, 2020 at 1:55 AM Simon Glass <sjg at chromium.org> wrote:
> > > > > > On Wed, 1 Apr 2020 at 11:39, Andy Shevchenko <andy.shevchenko at gmail.com> wrote:
> > > > > > > On Wed, Apr 01, 2020 at 10:56:26AM -0600, Simon Glass wrote:
> > > > > > > > On Wed, 1 Apr 2020 at 08:45, Andy Shevchenko <andy.shevchenko at gmail.com> wrote:
> > > > > > > > > On Wed, Apr 1, 2020 at 5:32 PM Bin Meng <bmeng.cn at gmail.com> wrote:
> > > > > > > > > > On Wed, Apr 1, 2020 at 9:58 PM Andy Shevchenko
> > > > > > > > > > <andriy.shevchenko at linux.intel.com> wrote:
> > > > > > > > > > >
> > > > > > > > > > > The commit breaks serial console on the Intel Edison.
> > > > > > > > > > >
> > > > > > > > > > > This reverts commit 720f9e1fdb0c92d3fd16e1bfc25bcbd35612675c.
> > > > > > > > > > >
> > > > > > > > > > > Signed-off-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
> > > > > > > > > > > ---
> > > > > > > > > > >  drivers/serial/ns16550.c | 40 ++++++++++++----------------------------
> > > > > > > > > > >  1 file changed, 12 insertions(+), 28 deletions(-)
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > Could you please spend some time to investigate why this breaks Intel Edison?
> > > > > > > > > >
> > > > > > > > > > Reverting this patch would mean we break other boards too as
> > > > > > > > > > Wolfgang's patch wanted to fix the breakage in the first place. Much
> > > > > > > > > > appreciated!
> > > > > > > > >
> > > > > > > > > I guess I'm wrong person here. The DM code is a complete black box to me.
> > > > > > > > > Nevertheless, I may test any provided fix / debug / etc patch by request.
> > > > > > > > >
> > > > > > > > > And I think it's fair to investigate by the one who made a regression
> > > > > > > > > in the first place.
> > > > > > > >
> > > > > > > > Given that we have conflicting breakages, we need to debug Edison.
> > > > > > >
> > > > > > > I would glad to test any suggested change or debug patch!
> > > > > > >
> > > > > > > > Does it enable the debug UART?
> > > > > > >
> > > > > > > If I am not mistaken, it does not.
> > > > > >
> > > > > > Looks like you are right. If you know the address you could do that -
> > > > > > see minnowmax for an example.
> > > > >
> > > > > Please suggest what's the best approach to proceed.
> > > >
> > > > I think I understand what happened, and Wolfgang's patch *is* a culprit.
> > > >
> > > > In serial_intel_mid.c we setup a divisor before probing the actual
> > > > device. Now, since the address retrieving has been moved further in
> > > > the initialization, we are writing to unknown registers and thus don't
> > > > properly initialize hardware.
> > >
> > > Yes, you are right, mid_serial_probe() relies on plat->base being set by
> > > ns16550_serial_ofdata_to_platdata().
> > >
> > > I was not aware that other drivers rely on ns16550 in this way.
> > > And now that I know I see that there are few more:
> > >
> > >   $ grep -r -l --include='*.c' -e ns16550_serial_probe -e ns16550_serial_ofdata_to_platdata
> > >   drivers/serial/serial_intel_mid.c
> > >   drivers/serial/serial_rockchip.c
> > >   drivers/serial/serial_omap.c
> > >   drivers/serial/ns16550.c
> > >   arch/x86/cpu/apollolake/uart.c
> > >   arch/x86/cpu/slimbootloader/serial.c
> > >
> > > This means my patch has a wider impact than what I have taken care of.
> > >
> > > @Bin: I'm fine with reverting 720f9e1 for now. I will come back with a
> > > new revision of this patch when I had the time to look at the other impacted
> > > drivers.
> > >
> > > But reverting 720f9e1 is IMHO only a temporary workaround, as the underlying
> > > problem (possible PCI access in ofdata_to_platdata()) should be fixed anyway,
> > > at least my interpretation of the comment in drivers/pci/pci-uclass.c is that
> > > this PCI access should not be there:
> > >
> > >     "A common cause of this problem is that this function is called in the
> > >     ofdata_to_platdata() method of @dev. Accessing the PCI bus in that
> > >     method is not allowed, since it has not yet been probed. To fix this,
> > >     move that access to the probe() method of @dev instead."
> > >
> >
> > Yes, when I looked at this, I wonder why the first commit was
> > introduced. Simon, could you please explain more about the DM changes
> > below?
>
> Yes, please see the cover letter for the series:
>
> https://www.mail-archive.com/u-boot@lists.denx.de/msg352249.html
>

Thanks. But still, as I described in my fix commit [1], there are
chances that any PCI based ns16550 driver might break due to the
ordering changes. Any ideas to improve that?

[1] http://patchwork.ozlabs.org/patch/1266326/

Regards,
Bin