linux-kernel - Re: [PATCH v2] serial: 8250_dw: Improve unwritable LCR workaround

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Date:	Fri, 06 Dec 2013 23:51:25 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	Tim Kryger <tim.kryger@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	patches@...aro.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Jason Cooper <jason@...edaemon.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] serial: 8250_dw: Improve unwritable LCR workaround

On Friday 06 December 2013 23:29:02 James Hogan wrote:
> So it looks like the LCR does always change immediately for me in this case
> (obviously it hasn't hit the BUSY case), but not all the bits can be
> written. In particular bit 5 and bit 7 at the least. If I do this (sorry
> for whitespace munging):
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c
> b/drivers/tty/serial/8250/8250_dw.c
> index 4658e3e..722d448 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -96,7 +96,7 @@ static void dw8250_serial_out(struct uart_port *p, int
> offset, int value)
>  	if (offset == UART_LCR) {
>  		int tries = 1000;
>  		while (tries--) {
> -			if (value == p->serial_in(p, UART_LCR))
> +			if (value & ~0xa0 == p->serial_in(p, UART_LCR) & ~0xa0)
>  				return;
>  			dw8250_force_idle(p);
>  			writeb(value, p->membase + (UART_LCR << p->regshift));
> @@ -132,7 +132,7 @@ static void dw8250_serial_out32(struct uart_port *p, int
> offset, int value)
>  	if (offset == UART_LCR) {
>  		int tries = 1000;
>  		while (tries--) {
> -			if (value == p->serial_in(p, UART_LCR))
> +			if (value & ~0xa0 == p->serial_in(p, UART_LCR) & ~0xa0)

My appologies, that should have had some more brackets (I should have retested 
after cleaning up my debugging). I.e.
+			if ((value & ~0xa0) == (p->serial_in(p, UART_LCR) & ~0xa0))

Cheers
James
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