Hi Philipp, > > > On 27 Oct 2017, at 00:13, Lukasz Majewski <[email protected]> wrote: > > > > It may happen that the serial IP block is performing some ongoing > > transmission (started at e.g. board_init()) when the serial "probe" > > is called. > > > > As a result the serial port IP block is reset, so transmitted data > > is corrupted: > > > > I2C: ready > > DRAM: 1 GiB > > jSS('HH��SL_SDHC: 04 rev 0x0 > > > > This patch prevents from this situation, by defining pre_probe() > > callback in which we wait till the TX buffer is empty (from > > previous transmission): > > > > I2C: ready > > DRAM: 1 GiB > > ID: unit type 0x4 rev 0x0 > > > > All defined ->pending callbacks at ./drivers/serial are non blocking > > - just simple reading from registers and testing flags. Hence, it > > should be enough to not use any timeout from timer. > > One shall also note that we enable console very early - not all > > timers may be ready for work - adding timeout here would impose > > implicit dependency that timers are setup before serial. > > Given that this is effectively a busy polling loop, why can’t this be > done from the probe-function of serial drivers that require this > functionality?
That would be one of the options. Originally, this code was placed at iMX specific function - namely _mxc_serial_init() [1]. However, Simon suggested to solve this problem globally via DM's serial-uclass, which offers pre_probe() callback for such purpose. The problem here is the polling loop. I've checked and ->pending on real SoCs is just a read from the register - which should not block (a similar approach is used in Linux kernel). Having timeout from timer would impose dependency on timer init'ed first - before serial. [1] - https://patchwork.ozlabs.org/patch/820824/ > > > > > > > Signed-off-by: Lukasz Majewski <[email protected]> > > --- > > > > drivers/serial/serial-uclass.c | 20 ++++++++++++++++++++ > > 1 file changed, 20 insertions(+) > > > > diff --git a/drivers/serial/serial-uclass.c > > b/drivers/serial/serial-uclass.c index 2e5116f..5e6964d 100644 > > --- a/drivers/serial/serial-uclass.c > > +++ b/drivers/serial/serial-uclass.c > > @@ -420,10 +420,30 @@ static int serial_pre_remove(struct udevice > > *dev) return 0; > > } > > > > +static int serial_pre_probe(struct udevice *dev) > > +{ > > + struct dm_serial_ops *ops = serial_get_ops(dev); > > + int ret = 0; > > + > > + /* > > + * Wait for any ongoing transmission to finish - for > > example > > + * from pre-relocation enabled UART > > + */ > > + if (ops && ops->pending) > > + do { > > + ret = ops->pending(dev, false); > > + if (ret < 0) > > + break; > > + } while (ret > 0); > > + > > + return ret; > > +} > > + > > UCLASS_DRIVER(serial) = { > > .id = UCLASS_SERIAL, > > .name = "serial", > > .flags = DM_UC_FLAG_SEQ_ALIAS, > > + .pre_probe = serial_pre_probe, > > .post_probe = serial_post_probe, > > .pre_remove = serial_pre_remove, > > .per_device_auto_alloc_size = sizeof(struct > > serial_dev_priv), -- > > 2.1.4 > > > Best regards, Lukasz Majewski -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: [email protected] _______________________________________________ U-Boot mailing list [email protected] https://lists.denx.de/listinfo/u-boot
