Am Freitag, den 17.07.2015, 09:10 -0400 schrieb Peter Hurley: > Hi Juergen, > > On 07/16/2015 03:40 AM, Juergen Borleis wrote: > > Whenever the UART device driver gets closed from userland, the driver > > disables the UART unit and then stops its clock to save power. > > > > The bit which disabled the UART unit is described as: > > > > "UART Enable. If this bit is set to 1, the UART is enabled. Data > > transmission and reception occurs for the UART signals. When the > > UART is disabled in the middle of transmission or reception, it > > completes the current character before stopping." > > > > The important part is the "it completes the current character". Whenever > > a reception is ongoing when the UART gets disabled (including the clock > > off) the statemachine freezes and "remembers" this state on the next > > open() and re-enabling of the unit's clock. > > > > In this case we end up receiving an additional bogus character > > immediately. > > > > The solution in this change is to move the AUART unit into its reset > > state on close() and only release it from its reset state on the next > > open(). > > > > Signed-off-by: Juergen Borleis <jbe@xxxxxxxxxxxxxx> > > --- > > > > Notes: > > v3: > > - missing newline added to an error message > > > > v2: > > - rename mxs_auart_do_reset() to mxs_auart_keep_reset() to better reflect > > what it really does > > - adapt the delay in mxs_auart_keep_reset() to wait for the reset of the > > AURAT unit to what is used in mxs_auart_reset() > > The function names and semantics are not clear. See below. [...] > > + /* bring it out of reset now */ > > + mxs_auart_reset(u); > > mxs_auart_reset() is really not resetting but simply performing a block enable. > Isn't there a generic block enable for the iMX.2x SoCs? (Maybe there should be) > > The names of these functions don't match expected operations of startup(). > Start up should be enabling the device, not keeping it in reset. > > And "keep reset" immediately followed by "reset" makes no sense. I'd call the pair mxs_auart_reset_assert and mxs_auart_reset_deassert. regards Philipp -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
