> 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? > > > 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 > _______________________________________________ U-Boot mailing list [email protected] https://lists.denx.de/listinfo/u-boot
