linux-kernel - Re: [PATCH] serial: 8250_omap: Implementation of Errata i2310

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Message-ID: <9ed7e96a-c538-aac1-5b52-b7b1d72bb6a0@linux.intel.com>
Date: Fri, 14 Jun 2024 11:28:23 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Udit Kumar <u-kumar1@...com>
cc: vigneshr@...com, nm@...com, Tony Lindgren <tony@...mide.com>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, u.kleine-koenig@...gutronix.de, 
    ronald.wahl@...itan.com, thomas.richard@...tlin.com, tglx@...utronix.de, 
    LKML <linux-kernel@...r.kernel.org>, 
    linux-serial <linux-serial@...r.kernel.org>
Subject: Re: [PATCH] serial: 8250_omap: Implementation of Errata i2310

On Fri, 14 Jun 2024, Udit Kumar wrote:

> As per Errata i2310[0], Erroneous timeout can be triggered,
> if this Erroneous interrupt is not cleared then it may leads
> to strom of interrupts, therefore apply Errata i2310 solution.
> 
> [0] https://www.ti.com/lit/pdf/sprz536 page 23
> 
> Signed-off-by: Udit Kumar <u-kumar1@...com>
> ---
>  drivers/tty/serial/8250/8250_omap.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 170639d12b2a..38eb639f78d3 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -115,6 +115,10 @@
>  /* RX FIFO occupancy indicator */
>  #define UART_OMAP_RX_LVL		0x19
>  
> +/* Timeout Low and High */
> +#define UART_OMAP_TO_L                 0x26
> +#define UART_OMAP_TO_H                 0x27
> +
>  /*
>   * Copy of the genpd flags for the console.
>   * Only used if console suspend is disabled
> @@ -663,13 +667,24 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)
>  
>  	/*
>  	 * On K3 SoCs, it is observed that RX TIMEOUT is signalled after
> -	 * FIFO has been drained, in which case a dummy read of RX FIFO
> -	 * is required to clear RX TIMEOUT condition.
> +	 * FIFO has been drained or erroneously.
> +	 * So apply solution of Errata i2310 as mentioned in
> +	 * https://www.ti.com/lit/pdf/sprz536
>  	 */
>  	if (priv->habit & UART_RX_TIMEOUT_QUIRK &&
> -	    (iir & UART_IIR_RX_TIMEOUT) == UART_IIR_RX_TIMEOUT &&
> -	    serial_port_in(port, UART_OMAP_RX_LVL) == 0) {
> -		serial_port_in(port, UART_RX);
> +		(iir & UART_IIR_RX_TIMEOUT) == UART_IIR_RX_TIMEOUT) {
> +		unsigned char efr2, timeout_h, timeout_l;
> +
> +		efr2 = serial_in(up, UART_OMAP_EFR2);
> +		timeout_h = serial_in(up, UART_OMAP_TO_H);
> +		timeout_l = serial_in(up, UART_OMAP_TO_L);
> +		serial_out(up, UART_OMAP_TO_H, 0xFF);
> +		serial_out(up, UART_OMAP_TO_L, 0xFF);
> +		serial_out(up, UART_OMAP_EFR2, 0x1);

Eh, this doesn't match the workaround in the errata???

Also, don't use literals but name the bits with defines (for the correct 
bit there's probably a pre-existing define but it's not named as good as 
it could be, I'd say it should be named as 
UART_OMAP_EFR2_TIMEOUT_PERIODIC).

> +		serial_in(up, UART_IIR);
> +		serial_out(up, UART_OMAP_EFR2, efr2);
> +		serial_out(up, UART_OMAP_TO_H, timeout_h);
> +		serial_out(up, UART_OMAP_TO_L, timeout_l);

-- 
 i.