linux-kernel - Re: Regression: commit c9712e333809 breaks xilinx

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Date:   Thu, 12 Sep 2019 07:53:08 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Paul Thomas <pthomas8589@...il.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>,
        Michal Simek <michal.simek@...inx.com>,
        Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Regression: commit c9712e333809 breaks xilinx_uartps

On 11. 09. 19 19:04, Paul Thomas wrote:
> Hello,
> 
> As I was working with a recent 5.2 kernel with a Zynq Ultrascale+
> board I found that the serial console wasn't working with a message
> like:
>  xuartps: probe of ff000000.serial failed with error -16
> 
> I did a git bisect and found that this came from:
>  commit: c9712e3338098359a82c3f5d198c92688fa6cd26
>  serial: uartps: Use the same dynamic major number for all ports
> 
> One difference I might have is in the device-tree, I'm using a proper
> clock config (zynqmp-clk-ccf.dtsi) using the firmware clock interface.
> This is absolutely necessary, for instance, with the Ethernet
> negotiation where the macb driver needs to change the clock rate. In
> any case I believe this pushes my case to the -EPROBE_DEFER when
> devm_clk_get() fails the first time, this might not have been tested
> in with the original submission. I'm not sure this makes everything
> completely correct, but the patch below does fix the issue for me.
> 
> thanks,
> Paul
> 
> ---
>  drivers/tty/serial/xilinx_uartps.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/tty/serial/xilinx_uartps.c
> b/drivers/tty/serial/xilinx_uartps.c
> index 9dcc4d855ddd..ece7f6caa994 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -1565,6 +1565,8 @@ static int cdns_uart_probe(struct platform_device *pdev)
> 
>         cdns_uart_data->pclk = devm_clk_get(&pdev->dev, "pclk");
>         if (PTR_ERR(cdns_uart_data->pclk) == -EPROBE_DEFER) {
> +               /* If we end up defering then set uartps_major back to 0 */
> +               uartps_major = 0;
>                 rc = PTR_ERR(cdns_uart_data->pclk);
>                 goto err_out_unregister_driver;
>         }
> 

I expect that this can be problematic for all failures in probe.
What about this? Just setting up global major number if first instance
pass.
Also cleanup should be likely done in remove function too.


 diff --git a/drivers/tty/serial/xilinx_uartps.c
b/drivers/tty/serial/xilinx_uartps.c
 index f145946f659b..c1550b45d59b 100644
 --- a/drivers/tty/serial/xilinx_uartps.c
 +++ b/drivers/tty/serial/xilinx_uartps.c
 @@ -1550,7 +1550,6 @@ static int cdns_uart_probe(struct platform_device
*pdev)
                 goto err_out_id;
         }

 -       uartps_major = cdns_uart_uart_driver->tty_driver->major;
         cdns_uart_data->cdns_uart_driver = cdns_uart_uart_driver;

         /*
 @@ -1680,6 +1679,7 @@ static int cdns_uart_probe(struct platform_device
*pdev)
                 console_port = NULL;
  #endif

 +       uartps_major = cdns_uart_uart_driver->tty_driver->major;
         cdns_uart_data->cts_override =
of_property_read_bool(pdev->dev.of_node,

"cts-override");
         return 0;

Thanks,
Michal