On 18-08-16, 12:11, Matwey V. Kornilov wrote:
> 2016-08-18 2:00 GMT+03:00 Viresh Kumar <viresh.kumar@xxxxxxxxxx>:
> > 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.
>
> I mean something like the following:
>
> static irqreturn_t omap8250_irq(int irq, void *dev_id)
> {
> struct uart_port *port = dev_id;
> struct uart_8250_port *up = up_to_u8250p(port);
> unsigned int iir;
> int ret;
>
> // fast_switch to the highest rate here
>
> #ifdef CONFIG_SERIAL_8250_DMA
> if (up->dma) {
> ret = omap_8250_dma_handle_irq(port);
> return IRQ_RETVAL(ret);
> }
> #endif
>
> serial8250_rpm_get(up);
> iir = serial_port_in(port, UART_IIR);
> ret = serial8250_handle_irq(port, iir);
> serial8250_rpm_put(up);
>
> // switch back here
>
> return IRQ_RETVAL(ret);
> }
>
> Probably, I've incorrectly understood the purpose of cpu freq fast switch.
Yes, you can't call that routine from this path directly.
--
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
