Messages in this thread | | | Subject | Re: [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger | From | Jiri Slaby <> | Date | Fri, 8 Jan 2021 08:58:38 +0100 |
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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.
thanks, -- js
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