Hi Philipp,
On 27 Oct 2017, at 00:13, Lukasz Majewski lukma@denx.de 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 lukma@denx.de
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 - forexample
* 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
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