linux-kernel - Re: [PATCH 06/16] tty: serial: Add 8250-core based omap driver

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Date:	Mon, 29 Sep 2014 11:38:23 +0200
From:	Frans Klaver <frans.klaver@...ns.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	<linux-serial@...r.kernel.org>, <tony@...mide.com>,
	<gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
	<balbi@...com>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 06/16] tty: serial: Add 8250-core based omap driver

On Wed, Sep 10, 2014 at 09:30:01PM +0200, Sebastian Andrzej Siewior wrote:
> +	/*
> +	 * We enable TRIG_GRANU for RX and TX and additionaly we set
> +	 * SCR_TX_EMPTY bit. The result is the following:
> +	 * - RX_TRIGGER amount of bytes in the FIFO will cause an interrupt.
> +	 * - less than RX_TRIGGER number of bytes will also cause an interrupt
> +	 *   once the UART decides that there no new bytes arriving.
> +	 * - Once THRE is enabled, the interrupt will be fired once the FIFO is
> +	 *   empty - the trigger level is ignored here.
> +	 *
> +	 * Once DMA is enabled:
> +	 * - UART will assert the TX DMA line once there is room for TX_TRIGGER
> +	 *   bytes in the TX FIFO. On each assert the DMA engine will move
> +	 *   TX_TRIGGER bytes into the FIFO.
> +	 * - UART will assert the RX DMA line once there are RX_TRIGGER bytes in
> +	 *   the FIFO and move RX_TRIGGER bytes.
> +	 * This is because treshold and trigger values are the same.

threshold

> +	/*
> +	 * It claims to be 16C750 compatible however it is a little different.
> +	 * It has EFR and has no FCR7_64byte bit. The AFE (which it claims to
> +	 * have) is enabled via EFR instead of MCR. The type is set here 8250
> +	 * just to get things going. UNKNOWN does not work for a few reasons and
> +	 * we don't need our own type since we don't use 8250's set_termios()
> +	 * and our "bugs" are handeld via the bug member.

handled

> +	 */
> +	up.port.type = PORT_8250;
> +	up.port.iotype = UPIO_MEM;
> +	up.port.flags = UPF_FIXED_PORT | UPF_FIXED_TYPE | UPF_SOFT_FLOW |
> +		UPF_HARD_FLOW;
> +	up.port.private_data = priv;
> +
> +	up.port.regshift = 2;
> +	up.port.fifosize = 64;
> +	up.tx_loadsz = 64;
> +	up.capabilities = UART_CAP_FIFO | UART_CAP_EFR | UART_CAP_SLEEP;
> +#ifdef CONFIG_PM_RUNTIME
> +	/*
> +	 * PM_RUNTIME is mostly transparent. However to do it right we need to a

need to _do_ a ...?

> +	 * TX empty interrupt before we can put the device to auto idle. So if
> +	 * PM_RUNTIME is not enabled we don't add that flag and can spare that
> +	 * one extra interrupt in the TX path.
> +	 */

<snip>

> +config SERIAL_8250_OMAP
> +	tristate "Support for OMAP internal UART (8250 based driver)"
> +	depends on SERIAL_8250 && ARCH_OMAP2PLUS
> +	help
> +	  If you have a machine based on an Texas Instruments OMAP CPU you
> +	  can enable its onboard serial ports by enabling this option.
> +
> +	  This driver is in early stage and uses ttyS instead of ttyO.
> +

I just wondered if this driver should be marked experimental?


Thanks,
Frans
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