linux-kernel - RE: [PATCH] tty: serial: fsl_lpuart: fix potential bug when using both of_alias_get_id and ida_simple

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Date:   Tue, 22 Mar 2022 02:07:48 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Shenwei Wang <shenwei.wang@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        Vabhav Sharma <vabhav.sharma@....com>
CC:     "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] tty: serial: fsl_lpuart: fix potential bug when using
 both of_alias_get_id and ida_simple_get

Hi Shenwei,

> > Subject: [PATCH] tty: serial: fsl_lpuart: fix potential bug when using
> > both of_alias_get_id and ida_simple_get
> >
> > Now fsl_lpuart driver use both of_alias_get_id() and ida_simple_get()
> > in .probe(), which has the potential bug. For example, when remove the
> > lpuart7 alias in dts, of_alias_get_id() will return error, then call
> > ida_simple_get() to allocate the id 0 for lpuart7, this may confilct
> > with the
> > lpuart4 which has alias 0.
> 
> The behavior of ida_simple_get() is to allocate an unused alias number. Do
> you see any conflict when you test?
> 

Yes, I have verified this on imx8ulp, I print the port.line value for each uart port.
When I remove the lpuart7 alias, the lpuart7 will get the id 0, same as lpuart4, which caused the lpuart7 probe fail.
ida_simple_get() cannot figure out which id has been used in the uart driver.

[    0.894549] port.line = 0 --> lpuart4
[    0.908148] port.line = 1 --> lpuart5
[    0.939844] port.line = 2 --> lpuart6
[    0.953608] port.line = 0 --> lpuart7

--- a/arch/arm64/boot/dts/freescale/imx8ulp.dtsi
+++ b/arch/arm64/boot/dts/freescale/imx8ulp.dtsi
@@ -25,7 +25,6 @@
                serial0 = &lpuart4;
                serial1 = &lpuart5;
                serial2 = &lpuart6;
-               serial3 = &lpuart7;
        };

Best regards
Sherry

> Regards,
> Shenwei
> 
> >
> >     aliases {
> > 	...
> >         serial0 = &lpuart4;
> >         serial1 = &lpuart5;
> >         serial2 = &lpuart6;
> >         serial3 = &lpuart7;
> >     }
> >
> > So remove the ida_simple_get() in .probe(), return an error directly
> > when calling
> > of_alias_get_id() fails, which is consistent with other uart drivers behavior.
> >
> > Fixes: 3bc3206e1c0f ("serial: fsl_lpuart: Remove the alias node
> > dependence")
> > Signed-off-by: Sherry Sun <sherry.sun@....com>
> > ---
> >  drivers/tty/serial/fsl_lpuart.c | 24 ++++--------------------
> >  1 file changed, 4 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > b/drivers/tty/serial/fsl_lpuart.c index 452a015825ba..40465d23d7ad
> > 100644
> > --- a/drivers/tty/serial/fsl_lpuart.c
> > +++ b/drivers/tty/serial/fsl_lpuart.c
> > @@ -239,8 +239,6 @@
> >  /* IMX lpuart has four extra unused regs located at the beginning */
> >  #define IMX_REG_OFF	0x10
> >
> > -static DEFINE_IDA(fsl_lpuart_ida);
> > -
> >  enum lpuart_type {
> >  	VF610_LPUART,
> >  	LS1021A_LPUART,
> > @@ -276,7 +274,6 @@ struct lpuart_port {
> >  	int			rx_dma_rng_buf_len;
> >  	unsigned int		dma_tx_nents;
> >  	wait_queue_head_t	dma_wait;
> > -	bool			id_allocated;
> >  };
> >
> >  struct lpuart_soc_data {
> > @@ -2716,23 +2713,18 @@ static int lpuart_probe(struct platform_device
> > *pdev)
> >
> >  	ret = of_alias_get_id(np, "serial");
> >  	if (ret < 0) {
> > -		ret = ida_simple_get(&fsl_lpuart_ida, 0, UART_NR,
> > GFP_KERNEL);
> > -		if (ret < 0) {
> > -			dev_err(&pdev->dev, "port line is full, add device
> > failed\n");
> > -			return ret;
> > -		}
> > -		sport->id_allocated = true;
> > +		dev_err(&pdev->dev, "failed to get alias id, errno %d\n", ret);
> > +		return ret;
> >  	}
> >  	if (ret >= ARRAY_SIZE(lpuart_ports)) {
> >  		dev_err(&pdev->dev, "serial%d out of range\n", ret);
> > -		ret = -EINVAL;
> > -		goto failed_out_of_range;
> > +		return -EINVAL;
> >  	}
> >  	sport->port.line = ret;
> >
> >  	ret = lpuart_enable_clks(sport);
> >  	if (ret)
> > -		goto failed_clock_enable;
> > +		return ret;
> >  	sport->port.uartclk = lpuart_get_baud_clk_rate(sport);
> >
> >  	lpuart_ports[sport->port.line] = sport; @@ -2781,10 +2773,6 @@
> > static int lpuart_probe(struct platform_device *pdev)
> >  failed_attach_port:
> >  failed_irq_request:
> >  	lpuart_disable_clks(sport);
> > -failed_clock_enable:
> > -failed_out_of_range:
> > -	if (sport->id_allocated)
> > -		ida_simple_remove(&fsl_lpuart_ida, sport->port.line);
> >  	return ret;
> >  }
> >
> > @@ -2794,9 +2782,6 @@ static int lpuart_remove(struct platform_device
> > *pdev)
> >
> >  	uart_remove_one_port(&lpuart_reg, &sport->port);
> >
> > -	if (sport->id_allocated)
> > -		ida_simple_remove(&fsl_lpuart_ida, sport->port.line);
> > -
> >  	lpuart_disable_clks(sport);
> >
> >  	if (sport->dma_tx_chan)
> > @@ -2926,7 +2911,6 @@ static int __init lpuart_serial_init(void)
> >
> >  static void __exit lpuart_serial_exit(void)  {
> > -	ida_destroy(&fsl_lpuart_ida);
> >  	platform_driver_unregister(&lpuart_driver);
> >  	uart_unregister_driver(&lpuart_reg);
> >  }
> > --
> > 2.17.1