Messages in this thread | | | Date | Fri, 8 Jan 2021 16:10:40 +0200 | From | Cristian Ciocaltea <> | Subject | Re: [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger |
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On Fri, Jan 08, 2021 at 08:58:38AM +0100, Jiri Slaby wrote: > On 07. 01. 21, 19:16, Cristian Ciocaltea wrote: > > Hi Greg, > > > > Thank you for the review! > > > > On Thu, Jan 07, 2021 at 04:20:55PM +0100, Greg Kroah-Hartman wrote: > > > On Tue, Jan 05, 2021 at 07:02:02PM +0200, Cristian Ciocaltea wrote: > > > > Implement 'poll_put_char' and 'poll_get_char' callbacks in struct > > > > 'owl_uart_ops' that enables OWL UART to be used for kernel debugging > > > > over serial line. > > > > > > > > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com> > > > > [...] > > > > > > + > > > > +static void owl_uart_poll_put_char(struct uart_port *port, unsigned char ch) > > > > +{ > > > > + while (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_TFFU) > > > > + cpu_relax(); > > > > > > Unbounded loops? What could possibly go wrong? > > > > > > :( > > > > > > Please don't do that in the kernel, put a max bound on this. > > > > I didn't realize the issue since I had encountered this pattern in many > > other serial drivers, as well: altera_uart, arc_uart, atmel_serial, etc. > > > > > And are you _SURE_ that cpu_relax() is what you want to call here? > > > > I'm thinking of replacing the loop with 'readl_poll_timeout_atomic()', > > if that would be a better approach. > > It might be better, yes. Either way, if you add a bound to the loop, you > definitely need a more precise timing, so ndelay/udelay instead of > cpu_relax.
I will use 1-5 us for the timing, but I'm not quite sure about the overall timeout - 10 ms would suffice?
Thanks, Cristi
> thanks, > -- > js
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