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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAYSxhpR664Od7AaWZrX0rE=iDUHo0h+4=uY=gvkFps4Hz4aew@mail.gmail.com>
Date:	Fri, 6 Dec 2013 16:31:38 -0800
From:	Tim Kryger <tim.kryger@...aro.org>
To:	James Hogan <james.hogan@...tec.com>
Cc:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	linux-serial@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Patch Tracking <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>,
	ARM Kernel List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] serial: 8250_dw: Improve unwritable LCR workaround

On Fri, Dec 6, 2013 at 3:51 PM, James Hogan <james.hogan@...tec.com> wrote:
> 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

James,

Thanks for the information.  This is really helpful.

You are right about bit 5 being a problem.  Its behavior differs
between IP versions 3.00a and 3.14c per the docs.

As for bit 7, when it doesn't change this indicates the UART was busy
and we need to do the workaround.

Would you mind testing it again using a mask of ~0x20?

Thanks,
Tim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/