[OpenWrt-Devel] mt7620a serial port driver ordering of nodes uart/uartlite vs ttyS0/ttyS1 patch

[Luis Soltero]

hm... it still seems that the board integrator should be able to determine the node name for the device.  Implementing a
scheme based on base address still hard wires the node name to the port and does not provide the flexibility of changing
it.    Absolutely depending on the load order is quirky... however knowing that gives you some flexibility in the naming.

I think the real answer is to add a property that allows you to specify the order.  Then you can order the devices
however you like.

i worry that implementing something on the base address is actually worse than what we currently have.

look forward to your thoughts.

--luis

On 8/30/14, 2:35 AM, John Crispin wrote:
> Hi
>
> On Lantiq we derive the port numbering from the base addr that gets
> used for early printk. i will implement a similar solution for ralink.
> having to rely on the load order seems quirky.
>
> 	John
>
> On 29/08/2014 23:56, Luis Soltero wrote:
>> Hello All,
>>
>> Most mt7620a routers defined in the target/linux/ramips/dts have
>> exactly one serial port defined which is used for the console.  The
>> serial port driver links this to node /dev/ttyS0.
>>
>> However.  one (and now 2) devices use the mt7620a serial port lines
>> for use as a second real serial port (uart at 500 in the dts).
>> Currently when when more than one serial port is defined  the boot
>> sequence starts with the console attached to uartlite but as soon
>> as the serial port driver driver is loaded it deactivates the
>> console and assigns it to /dev/ttyS1 (which is the node created for
>> uartlite).  So on these systems using the standard dts
>> configuration the mt7620a enhanced uart is bound to /dev/ttyS0 and
>> uartlite is bound /dev/ttyS1.
>>
>> This causes the console serial port to stop displaying output
>> unless the following is added to the dts definition
>>
>> chosen { bootargs = "console=ttyS1,57600"; };
>>
>> which redefines the console to /dev/ttyS1... this configuration
>> works fine.   However some (including me) find this very 
>> irritating.  These few routers defining a second serial port differ
>> from all the others in their definition of /dev/ttyS0 as the
>> console.
>>
>> So... for consistency it seems that it would be much better for **
>> ALL ** routers regardless of the number of serial ports define
>> /dev/ttyS0 as the console port.
>>
>> The reason for the renumbering is due to the serial port driver to
>> assign nodes on a first come first basis in the dts definition.
>> Since in mt7620a.dtsi (included by most/all 7620a router board
>> definitions) the definition for uart at 500 is before that for
>> uartlite at 00.  So  uart gets assigned /dev/ttyS0 while uartlite gets
>> /dev/ttyS1.  You can't fault the serial driver for doing it.  After
>> all it really doesn't know for what purpose the serial port is to
>> be used.
>>
>> A logical extension to the serial port dts properties would be to
>> add a "node-name" or "node-order" or "node-number" property that
>> would allow the integrator to specify the node number or the node
>> name for the serial port. However these properties don't exist (or
>> at least they were not obvious in either the source code or the
>> documentation).  So... a simple "fix" for the ordering is to
>> reorder the definitions in mt7620a.dtsi.
>>
>> This reordering affects exactly one mt7620a router in the dts
>> definitions as of r42293 (NA930.dts).
>>
>> Attached you will find a patch which modifies both mt7620a.dtsi and
>> NA930.dts assigning the console to /dev/ttyS0 for devices with more
>> than one serial port.
>>
>> Note that a similar issue applies to the RT5350.  Although we are
>> currently not working with that architecture I am happy to supply a
>> patch if the community would like one.
>>
>> here is a snippet from the boot log of our mt7620a board showing a
>> console happily bound to /dev/ttyS0 and the second serial port
>> bound to /dev/ttyS1
>>
>> [    0.350000] Serial: 8250/16550 driver, 2 ports, IRQ sharing
>> disabled [    0.370000] 10000c00.uartlite: ttyS0 at MMIO 0x10000c00
>> (irq = 20) is a 16550A [    0.380000] console [ttyS0] enabled,
>> bootconsole disabled [    0.380000] console [ttyS0] enabled,
>> bootconsole disabled [    0.410000] 10000500.uart: ttyS1 at MMIO
>> 0x10000500 (irq = 13) is a 16550A
>>
>>
>> --luis
>>
>>
>>
>>
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-- 


Luis Soltero, Ph.D., MCS
Director of Software Development, CTO
Global Marine Networks, LLC
StarPilot, LLC
Tel: +1.865.379.8723
Fax: +1.865.681.5017
E-Mail: lsoltero at globalmarinenet.net
Web: http://www.globalmarinenet.net
Web: http://www.redportglobal.com
Web: http://www.starpilotllc.com
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