[PATCH] tty: xilinx_uartps: Really fix id assignment

[Michal Simek]

Hi,

On 09. 07. 20 9:48, Helmut Grohne wrote:
> The problems started with the revert (18cc7ac8a28e28). The
> cdns_uart_console.index is statically assigned -1. When the port is
> registered, Linux assigns consecutive numbers to it. It turned out that
> when using ttyPS1 as console, the index is not updated as we are reusing
> the same cdns_uart_console instance for multiple ports. When registering
> ttyPS0, it gets updated from -1 to 0, but when registering ttyPS1, it
> already is 0 and not updated.
> 
> That led to 2ae11c46d5fdc4. It assigns the index prior to registering
> the uart_driver once. Unfortunately, that ended up breaking the
> situation where the probe order does not match the id order. When using
> the same device tree for both uboot and linux, it is important that the
> serial0 alias points to the console. So some boards reverse those
> aliases. This was reported by Jan Kiszka. The proposed fix was reverting
> the index assignment and going back to the previous iteration.
> 
> However such a reversed assignement (serial0 -> uart1, serial1 -> uart0)
> was already partially broken by the revert (18cc7ac8a28e28). While the
> ttyPS device works, the kmsg connection is already broken and kernel
> messages go missing. Reverting the id assignment does not fix this.
> 
> From the xilinx_uartps driver pov (after reverting the refactoring
> commits), there can be only one console. This manifests in static
> variables console_pprt and cdns_uart_console. These variables are not
> properly linked and can go out of sync. The cdns_uart_console.index is
> important for uart_add_one_port. We call that function for each port -
> one of which hopefully is the console. If it isn't, the CON_ENABLED flag
> is not set and console_port is cleared. The next cdns_uart_probe call
> then tries to register the next port using that same cdns_uart_console.
> 
> It is important that console_port and cdns_uart_console (and its index
> in particular) stay in sync. The index assignment implemented by
> Shubhrajyoti Datta is correct in principle. It just may have to happen a
> second time if the first cdns_uart_probe call didn't encounter the
> console device. And we shouldn't change the index once the console uart
> is registered.
> 
> Reported-by: Shubhrajyoti Datta <shubhrajyoti.datta at xilinx.com>
> Reported-by: Jan Kiszka <jan.kiszka at web.de>
> Link: https://lore.kernel.org/linux-serial/f4092727-d8f5-5f91-2c9f-76643aace993@siemens.com/
> Fixes: 18cc7ac8a28e28 ("Revert "serial: uartps: Register own uart console and driver structures"")
> Fixes: 2ae11c46d5fdc4 ("tty: xilinx_uartps: Fix missing id assignment to the console")
> Signed-off-by: Helmut Grohne <helmut.grohne at intenta.de>
> ---
>  drivers/tty/serial/xilinx_uartps.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index b9d672af8b65..2833f1418d6d 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -1465,7 +1465,6 @@ static int cdns_uart_probe(struct platform_device *pdev)
>  		cdns_uart_uart_driver.nr = CDNS_UART_NR_PORTS;
>  #ifdef CONFIG_SERIAL_XILINX_PS_UART_CONSOLE
>  		cdns_uart_uart_driver.cons = &cdns_uart_console;
> -		cdns_uart_console.index = id;
>  #endif
>  
>  		rc = uart_register_driver(&cdns_uart_uart_driver);
> @@ -1581,8 +1580,10 @@ static int cdns_uart_probe(struct platform_device *pdev)
>  	 * If register_console() don't assign value, then console_port pointer
>  	 * is cleanup.
>  	 */
> -	if (!console_port)
> +	if (!console_port) {
> +		cdns_uart_console.index = id;
>  		console_port = port;
> +	}
>  #endif
>  
>  	rc = uart_add_one_port(&cdns_uart_uart_driver, port);
> @@ -1595,8 +1596,10 @@ static int cdns_uart_probe(struct platform_device *pdev)
>  #ifdef CONFIG_SERIAL_XILINX_PS_UART_CONSOLE
>  	/* This is not port which is used for console that's why clean it up */
>  	if (console_port == port &&
> -	    !(cdns_uart_uart_driver.cons->flags & CON_ENABLED))
> +	    !(cdns_uart_uart_driver.cons->flags & CON_ENABLED)) {
>  		console_port = NULL;
> +		cdns_uart_console.index = -1;
> +	}
>  #endif
>  
>  	cdns_uart_data->cts_override = of_property_read_bool(pdev->dev.of_node,
> 

Thanks for the patch. I think that it will be very useful to list out
all testcases to make sure that we test all that scenarios and finally
get over it.
We are testing scenarios and likely we are missing some that we are not
able catch all issues before we submit a patch.

Thanks,
Michal