8250.c::autoconfig() fails loopback test on MPC824[15]

[Guennadi Liakhovetski]

On Sun, 5 Aug 2007, Arnd Bergmann wrote:

> On Sunday 05 August 2007, Guennadi Liakhovetski wrote:
> > I tried using of_serial.c on a (PPC) MPC8241 based system, which has a 
> > "16650A" compatible double UART built into the SoC. Using of_serial.c 
> > causes the ports to be autoconfigured, and this fails. The loopback test 
> > fails, because the MSR register on 824[15] doesn't implement the 
> > UART_MSR_DCD bit. Question: what's better, teach 8250.c to handle UARTs 
> > without this bit, or set the UPF_SKIP_TEST bit in of_serial.c for these 
> > SOCs to skip the loopback test altogether? The latter is certainly easier 
> > and affects much fewer systems, so, I'd go for that.
> 
> Yes, that sounds good. Just make sure you test the "compatible" property
> in the device node for something appropriate. In of_platform_serial_probe(),
> you can then do something like
> 
> 	if (of_device_is_compatible(ofdev, "mpc8241-serial"))
> 		flags |= UPF_SKIP_TEST;

That would be a possibility, but that would mean all 8241/8245 have to 
adjust their .dts. Ok, there are not so many of them in the mainline now 
(in fact, hardly any apart from linkstation:-)), still. Cannot we use 
something already available to just check if we're running on such a CPU? 
Worst case - find and parse cpu node, or maybe using some cpu_feature?

Thanks
Guennadi
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Guennadi Liakhovetski