From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH v2 1/4] tty: serial: Add 8250 earlycon to support noinit option Date: Sun, 01 Feb 2015 22:45:12 -0500 Message-ID: <54CEF2C8.1050808@hurleysoftware.com> References: <1421068104-30463-1-git-send-email-eddie.huang@mediatek.com> <1421068104-30463-2-git-send-email-eddie.huang@mediatek.com> <54CE53F3.5040709@hurleysoftware.com> <54CE6FD9.5030606@hurleysoftware.com> <1422846994.5512.25.camel@mtksdaap41> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1422846994.5512.25.camel@mtksdaap41> Sender: linux-doc-owner@vger.kernel.org To: Eddie Huang Cc: Rob Herring , Mark Rutland , Greg Kroah-Hartman , Matthias Brugger , devicetree@vger.kernel.org, Vladimir Murzin , srv_heupstream@mediatek.com, Pawel Moll , Ian Campbell , Catalin Marinas , Jonathan Corbet , Will Deacon , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, yh.chen@mediatek.com, Howard Chen , Ashwin Chaugule , linux-serial@vger.kernel.org, Kumar Gala , "Joe.C" , Jiri Slaby , linux-arm-kernel@lists.infradead.org, Alan Cox List-Id: devicetree@vger.kernel.org On 02/01/2015 10:16 PM, Eddie Huang wrote: > Hi Peter, > > On Sun, 2015-02-01 at 13:26 -0500, Peter Hurley wrote: >> On 02/01/2015 11:27 AM, Peter Hurley wrote: >>> Hi Eddie, >>> >>> On 01/12/2015 08:08 AM, Eddie Huang wrote: >>>> Add earlycon support not only baudrate option, but also add noinit option. >>>> If use noinit option, 8250 earlycon will not init serial hardware and use >>>> loader setting. >>> >>> I see this went into Greg's tty-testing branch. >>> >>> The only point of this is to not program the divisor, right? >>> >>> I ask because early_serial8250_setup() could already handle this without >>> extra options by simply not doing divisor programming if no baud option is >>> present. >> >> Does the patch below work for your use-case? >> >> [ Note: the patch applies to 3.19-rcX. To test, your noinit patches need to be >> reverted first. >> ] >> >> --- >% --- >> From: Peter Hurley >> Subject: [PATCH] serial: 8250_early: Assume uart already initialized if no >> baud option >> >> The option string is not supplied if the earlycon >> is started via devicetree and OF_EARLYCON_DECLARE(). The option string >> is also not required if started via kernel command line parameters of >> the form: >> earlycon=uart,mmio, >> console=uart,mmio, >> >> If earlycon_device->baud is 0, then an option string was not supplied. >> In this case, assume the uart has already been initialized by the >> bootloader or firmware. >> >> Signed-off-by: Peter Hurley >> --- >> drivers/tty/serial/8250/8250_early.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c >> index d7b831b..1701d00 100644 >> --- a/drivers/tty/serial/8250/8250_early.c >> +++ b/drivers/tty/serial/8250/8250_early.c >> @@ -149,12 +149,18 @@ static int __init early_serial8250_setup(struct earlycon_device *device, >> return 0; >> >> if (!device->baud) { >> + struct uart_port *port = &device->port; >> + unsigned int ier; >> + >> device->baud = probe_baud(&device->port); >> snprintf(device->options, sizeof(device->options), "%u", >> device->baud); >> - } >> >> - init_port(device); >> + /* assume the device was initialized, only mask interrupts */ >> + ier = serial8250_early_in(port, UART_IER); >> + serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); >> + } else >> + init_port(device); > Should add brace in else. I don't do that unless I have to. > Where is original line here. > early_device = device; Whoops :) I wrote the patch from a private branch which implements extensible console matching (so a console can define its own match function) and a bunch of other console cleanup and code removal. In that series, early_device becomes unnecessary and is removed. I'll respin proper patches on top of Greg's tty-testing branch with reverts for the noinit options. I noticed that one of the noinit patches actually has the linkage for the mtk earlycon, so I'll be sure to preserve that. Regards, Peter Hurley