[PATCH v2] drivers: serial: probe all uart devices

[Vabhav Sharma (OSS)]

Hi Simon,
Apology for delayed reply, Got occupied due to other business deliverables

> -----Original Message-----
> From: Simon Glass <sjg at chromium.org>
> Sent: Wednesday, September 30, 2020 10:15 PM
> To: Vabhav Sharma (OSS) <vabhav.sharma at oss.nxp.com>
> Cc: Andre Przywara <andre.przywara at arm.com>; U-Boot Mailing List <u-
> boot at lists.denx.de>; Stefan Roese <sr at denx.de>; Vabhav Sharma
> <vabhav.sharma at nxp.com>
> Subject: Re: [PATCH v2] drivers: serial: probe all uart devices
> 
> Hi Vabhav,
> 
> On Tue, 29 Sep 2020 at 11:33, Vabhav Sharma <vabhav.sharma at oss.nxp.com>
> wrote:
> >
> > From: Vabhav Sharma <vabhav.sharma at nxp.com>
> >
> > U-Boot DM model probe only single device at a time which is enabled
> > and configured using device tree or platform data method.
> >
> > PL011 UART IP is SBSA compliant and firmware does the serial port
> > set-up, initialization and let the kernel use UART port for sending
> > and receiving characters.
> >
> > Normally software talk to one serial port time but some LayerScape
> > platform require all the UART devices enabled in Linux for various use
> > case.
> >
> > Adding support to probe all enabled serial devices like SBSA compliant
> > PL011 UART ports probe and initialization by firmware.
> >
> > Signed-off-by: Vabhav Sharma <vabhav.sharma at nxp.com>
> > ---
> > v2:
> >    Incorporated Stefan review comment, Update #ifdef with macro
> >    if (IS_ENABLED)..
> > ---
> > ---
> >  drivers/serial/Kconfig         | 17 +++++++++++++++++
> >  drivers/serial/serial-uclass.c | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 47 insertions(+)
> >
> > diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig index
> > e344677..b2e30f1 100644
> > --- a/drivers/serial/Kconfig
> > +++ b/drivers/serial/Kconfig
> > @@ -134,6 +134,23 @@ config SERIAL_SEARCH_ALL
> >
> >           If unsure, say N.
> >
> > +config SERIAL_PROBE_ALL
> > +       bool "Probe all available serial devices"
> > +       depends on DM_SERIAL
> > +       default n
> 
> not needed
> 
> > +       help
> > +         The serial subsystem only probe for single serial device,
> > +         but does not probe for other remaining serial devices.
> > +         With this option set,we make probing and searching for
> > +         all available devices optional.
> > +         Normally, U-Boot talk to one serial port at a time but SBSA
> > +         compliant UART devices like PL011 require initialization
> > +         by firmware and let the kernel use serial port for sending
> > +         and receiving the characters.
> > +
> > +         If probing is not required for all remaining available
> > +         devices other than default current console device, say N.
> > +
> >  config SPL_DM_SERIAL
> >         bool "Enable Driver Model for serial drivers in SPL"
> >         depends on DM_SERIAL && SPL_DM diff --git
> > a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
> > index 0027625..d303a66 100644
> > --- a/drivers/serial/serial-uclass.c
> > +++ b/drivers/serial/serial-uclass.c
> > @@ -86,6 +86,11 @@ static void serial_find_console_or_panic(void)
> >                 uclass_first_device(UCLASS_SERIAL, &dev);
> >                 if (dev) {
> >                         gd->cur_serial_dev = dev;
> > +                       if (IS_ENABLED(CONFIG_SERIAL_PROBE_ALL)) {
> > +                               /* Scanning uclass to probe all devices */
> > +                               for (; dev; uclass_next_device(&dev))
> > +                                       ;
> 
> Please put this into a function in drivers/core/uclass.c since this is a useful
> function. E.g. uclass_probe_all(enum uclass_id)
> 
> Also you could use device_foreach_child_probe().
> 
> Can you put this in the only caller of serial_find_console_or_panic() instead?
>
Ok, Let me check the above the above functions feasibility to probe serial ports
> Do you ever have a situation where there is no serial console in U-Boot but
> you still want to probe everything? If so, a better place might be at the end
> of dm_init_and_scan().
I see, Situation is rare but possible as SBSA compliance required initialization by firmware.
> 
> Finally, do you want to do this in SPL as well, or is it enough to just do it in U-
> Boot proper? If the latter you could use
> 
> if (CONFIG_IS_ENABLED(SERIAL_PROBE_ALL)) { // do it } Regards, Simon,
Ok, Both are possible as per the requirement.

Current changes target PL011 UART IP which is SBSA compliant and accordingly used Serial uclass functions to do the needful.