Hi Kevin... On 01/05/2011 07:26 AM, Michael Williamson wrote: > On the da850/omap-l138/am18x family of SoCs, up to three on chip UARTS may be > configured. These peripherals support the standard Tx/Rx signals as well as > CTS/RTS hardware flow control signals. The pins on these SOC's associated with > these signals are multiplexed; e.g., the pin providing UART0_TXD capability > also provides SPI0 chip select line 5 output capability. The configuration of > the pin multiplexing occurs during platform initialization (or by earlier > bootloader operations). > > There is a problem with the multiplexing implementation on these SOCs. Only > the output and output enable portions of the I/O section of the pin are > multiplexed. All peripheral input functions remain connected to a given pin > regardless of configuration. > > In many configurations of these parts, providing a UART with Tx/Rx capability > is needed, but the HW flow control capability is not. Furthermore, the pins > associated with the CTS inputs on these UARTS are often configured to support > a different peripheral, and they may be active/toggling during runtime. This > can result in false modem status (CTS) interrupts being asserted to the 8250 > driver controlling the associated Tx/Rx pins, and will impact system > performance. > > The 8250 serial driver platform data does not provide a direct mechanism to > tell the driver to disable modem status (i.e., CTS) interrupts for a given > port. As a work-around, intercept register writes to the IER and disable > modem status interrupts. > > This patch was tested using a MityDSP-L138 SOM having UART1 enabled with the > associated CTS pin connected to a clock (configured for the AHCLKX function). > > Background / problem reports related to this issue are captured in the links > below: > http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/36701.aspx > http://www.mail-archive.com/davinci-linux-open-source@xxxxxxxxxxxxxxxxxxxx/msg19524.html > > Signed-off-by: Michael Williamson <michael.williamson@xxxxxxxxxxxxxxxx> > Tested-by: Michael Williamson <michael.williamson@xxxxxxxxxxxxxxxx> > --- > This is against the linux-davinci tree. > > Changes from original proposed patch: > - instead of overriding set_termios, now override serial_out driver hook > and intercept writes to the MSR. > > An alternate patch was proposed that modified the serial core driver and added a UPF_NO_MSR > flag. There was resistance to this patch. The reasoning is that the core 8250 driver code > should not continue to get muddied by platform hacks. > I'd like to withdraw this patch. It works, but it's inefficient and ugly, and I also get the feeling it isn't going to make it in it's current form anyway. I have another patch that is limited to just the mityomapl138 platform that I would like to submit in place of this. No other board appears to have this problem, so it makes sense to constrain the fix to platform file that does. -Mike -- 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
