linux-kernel - Re: [PATCH 3/4] serial: 8250_dw: Add UPF_FIXED

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Date:	Wed, 22 Jul 2015 08:38:59 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Noam Camus <noamc@...hip.com>
CC:	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Alexey.Brodkin@...opsys.com, vgupta@...opsys.com,
	gregkh@...uxfoundation.org, jslaby@...e.com
Subject: Re: [PATCH 3/4] serial: 8250_dw: Add UPF_FIXED_TYPE to flags

Hi Noam,

On 07/22/2015 05:34 AM, Noam Camus wrote:
> From: Noam Camus <noamc@...hip.com>
> 
> Always add UPF_FIXED_TYPE to flags so autoconf() will be skipped.
> We do that since autoconf() performs many writes to LCR that cause
> BUSY interrupt.
> The problem with such interrupt is that driver is not yet called to
> request_irq() and generic IRQ subsystem will mask the UART line.
> 
> Signed-off-by: Noam Camus <noamc@...hip.com>
> ---
>  drivers/tty/serial/8250/8250_dw.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index 1a57105..620f983 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -362,6 +362,14 @@ static int dw8250_probe_of(struct uart_port *p,
>  	if (has_ucv)
>  		dw8250_setup_port(up);
>  
> +	/* Writing to LCR may cause BUSY interrupt before we
> +	 * register the IRQ line.
> +	 * Currently autoconf() uses several writes to LCR.
> +	 * In order to avoid calling to autoconf() always add
> +	 * following flag.
> +	 */
> +	p->flags |= UPF_FIXED_TYPE;

Why only for devicetree DW8250's?  Don't all DW8250's have this LCR "feature"?

And what port type does this id DW8250's as, PORT_8250? Except with fifos,
autoflow control, dma, etc.?

If the port type is being fixed, then please fix it to a new port type.

> +
>  	/* if we have a valid fifosize, try hooking up DMA here */
>  	if (p->fifosize) {
>  		up->dma = &data->dma;
> 

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