On 17-08-16, 18:35, Matwey V. Kornilov wrote: > Hello, > > Does anybody know whether it is possible to implement fast_switch() > for cpufreq module used on am335x (like BeagleBone)? > I would like to use fast_switch feature in my software driver rs485 > duplex control implementation in tty/serial/8250/8250_port.c > Recently I've faced an timing issue with it. Depending on current CPU > on BeagleBone Black it takes from 40 usec to 200 usec to handle UART > IRQ. > Consequently, it takes 40-200 usec to switch transfer direction after > the last char transmitted. > It appeared that there are peripheral which start transmission after > about 60 usec after last char received (When BeagleBone is not quick > enough to switch direction to that time, the data go to nowhere). > In order to avoid input data loss, I have to set CPU governor to > `performance' on each boot. > I suppose it would be great to use CPU frequency fast switching in > UART IRQ handling when delay_rts_after_send is set to 0 in order to > avoid similar issues. You mean that you want to update frequency of the cpu from your tty driver? I am not sure if its a good idea really. CPU frequency is governed by cpufreq governors, which evaluate the load at run time and based on that take a decision to increase/decrease the frequency. -- viresh -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
