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Message-ID: <d59a3140-b701-4443-b160-a880fc7fc824@tuxon.dev>
Date: Sat, 21 Dec 2024 11:39:12 +0200
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: gregkh@...uxfoundation.org, jirislaby@...nel.org,
wsa+renesas@...g-engineering.com, prabhakar.mahadev-lad.rj@...renesas.com,
lethal@...ux-sh.org, g.liakhovetski@....de, groeck@...omium.org,
mka@...omium.org, ulrich.hecht+renesas@...il.com,
ysato@...rs.sourceforge.jp, linux-kernel@...r.kernel.org,
linux-serial@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, stable@...r.kernel.org
Subject: Re: [PATCH RFT 5/6] serial: sh-sci: Clean sci_ports[0] after at
earlycon exit
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@...on.dev> wrote:
>> From: Claudiu Beznea <claudiu.beznea.uj@...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@...r.kernel.org
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...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@...ux-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
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