Re: [PATCH RFT 5/6] serial: sh-sci: Clean sci_ports[0] after at earlycon exit

[Claudiu Beznea <claudiu.beznea@tuxon.dev>]

Hi, Geert,

On 19.12.2024 16:26, Geert Uytterhoeven wrote:
> Hi Claudiu,
> 
> On Wed, Dec 4, 2024 at 4:58 PM Claudiu <claudiu.beznea@tuxon.dev> wrote:
>> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>>
>> The early_console_setup() function initializes sci_ports[0].port with an
>> object of type struct uart_port obtained from the struct earlycon_device
>> passed as an argument to early_console_setup().
>>
>> Later, during serial port probing, the serial port used as earlycon
>> (e.g., port A) might be remapped to a different position in the sci_ports[]
>> array, and a different serial port (e.g., port B) might be assigned to slot
>> 0. For example:
>>
>> sci_ports[0] = port B
>> sci_ports[X] = port A
>>
>> In this scenario, the new port mapped at index zero (port B) retains the
>> data associated with the earlycon configuration. Consequently, after the
>> Linux boot process, any access to the serial port now mapped to
>> sci_ports[0] (port B) will block the original earlycon port (port A).
>>
>> To address this, introduce an early_console_exit() function to clean up
>> sci_ports[0] when earlycon is exited.
>>
>> To prevent the cleanup of sci_ports[0] while the serial device is still
>> being used by earlycon, introduce the struct sci_port::probing flag and
>> account for it in early_console_exit().
>>
>> Fixes: 0b0cced19ab1 ("serial: sh-sci: Add CONFIG_SERIAL_EARLYCON support")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>> ---
>>
>> Changes since the integrated patch:
>> - adjust the commit message to address Geert comments at [1]
>> - Introduce the struct sci_port::probing flag to prevent the cleanup
>>   of sci_ports[0] while the serial device is still being used by earlycon
> 
> Thanks for the update!
> 
>> --- a/drivers/tty/serial/sh-sci.c
>> +++ b/drivers/tty/serial/sh-sci.c
>> @@ -159,6 +159,7 @@ struct sci_port {
>>         bool autorts;
>>         bool tx_occurred;
>>         bool earlycon;
>> +       bool probing;
> 
> This is only used in sci_ports[0], so it can be a single global flag,
> instead of a flag embedded in each sci_port structure.
> 
>>  };
>>
>>  #define SCI_NPORTS CONFIG_SERIAL_SH_SCI_NR_UARTS
>> @@ -3386,7 +3387,8 @@ static struct plat_sci_port *sci_parse_dt(struct platform_device *pdev,
>>  static int sci_probe_single(struct platform_device *dev,
>>                                       unsigned int index,
>>                                       struct plat_sci_port *p,
>> -                                     struct sci_port *sciport)
>> +                                     struct sci_port *sciport,
>> +                                     struct resource *sci_res)
>>  {
>>         int ret;
>>
>> @@ -3433,12 +3435,15 @@ static int sci_probe_single(struct platform_device *dev,
>>                 sciport->port.flags |= UPF_HARD_FLOW;
>>         }
>>
>> -       ret = uart_add_one_port(&sci_uart_driver, &sciport->port);
>> -       if (ret) {
>> -               return ret;
>> +       if (sci_ports[0].earlycon && sci_ports[0].port.mapbase == sci_res->start) {
>> +               /*
>> +                * Skip cleanup up the sci_port[0] in early_console_exit(), this
> 
> Double up
> 
>> +                * port is the same as the earlycon one.
>> +                */
>> +               sci_ports[0].probing = true;
>>         }
>>
>> -       return 0;
>> +       return uart_add_one_port(&sci_uart_driver, &sciport->port);
>>  }
>>
>>  static int sci_probe(struct platform_device *dev)
>> @@ -3496,7 +3501,7 @@ static int sci_probe(struct platform_device *dev)
>>
>>         platform_set_drvdata(dev, sp);
>>
>> -       ret = sci_probe_single(dev, dev_id, p, sp);
>> +       ret = sci_probe_single(dev, dev_id, p, sp, res);
>>         if (ret)
>>                 return ret;
>>
>> @@ -3579,6 +3584,20 @@ sh_early_platform_init_buffer("earlyprintk", &sci_driver,
>>  #ifdef CONFIG_SERIAL_SH_SCI_EARLYCON
>>  static struct plat_sci_port port_cfg;
>>
>> +static int early_console_exit(struct console *co)
>> +{
>> +       struct sci_port *sci_port = &sci_ports[0];
>> +
>> +       /*
>> +        * Clean the slot used by earlycon. A new SCI device might
>> +        * map to this slot.
>> +        */
>> +       if (sci_port->earlycon && !sci_port->probing)
>> +               memset(sci_port, 0, sizeof(*sci_port));
> 
> Aha, so this clears sci_port.earlycon, too (cfr. my comment on
> PATCH 4/6). Still, I don't think this is sufficient: shouldn't
> sci_port.earlycon be cleared unconditionally?

I remember I had failures with unconditional clear. I'll double check it
though and adjust accordingly, if needed.

Thank you,
Claudiu

> 
>> +
>> +       return 0;
>> +}
>> +
>>  static int __init early_console_setup(struct earlycon_device *device,
>>                                       int type)
>>  {
>> @@ -3596,6 +3615,8 @@ static int __init early_console_setup(struct earlycon_device *device,
>>                        SCSCR_RE | SCSCR_TE | port_cfg.scscr);
>>
>>         device->con->write = serial_console_write;
>> +       device->con->exit = early_console_exit;
>> +
>>         return 0;
>>  }
>>  static int __init sci_early_console_setup(struct earlycon_device *device,
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds