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:

quoted

On Tue, Jan 05, 2021 at 07:02:02PM +0200, Cristian Ciocaltea wrote:

quoted

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>

[...]

quoted

quoted

+
+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.

quoted

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